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Location: Bergen, Norway
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PS: As I wrote in an earlier post, I used wrong temperature values in my first post as I though 80 C was with the gauge needle in center between the two lines, but later Chicks posted the picture which shows that 90 C is where the needle "should be at". I have now edited my first post to reflect my problem correctly.

As my needle never gets above 100 C, I guess the high speed setting never kicks in on my fans. If I change from my stock 92/102 fan switch to a 85/92 fan switch, then I think that should actually solve the problem I have (As long as my oil temps aren't too high, which is really my main concern).

But, what are the draw backs with using the 85/92 fan switch? I assume the fans will be running at low speed more or less constantly since my thermostat is also set at 85 C?
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Paul E. Johannessen from Bergen in Norway

- 1972 Porsche 911, rebuilt to '76 Carrera 3.0 spec
- 1986 Porsche 944 Turbo
Old 08-15-2014, 11:57 PM
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Ornery Bastard
 
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Quote:
Originally Posted by flash968 View Post
lol - nope - sorry aaron. there are plenty of us who have the same experience, especially those of us who are supercharged. it's really not a big deal. almost every time i run into somebody who does not have that experience, it is because they made the huge mistake of removing the belly pans, or has been running tap water, or has not changed their coolant in over 3 years. properly clean, filled, bled, and set up, the system will NOT fluctuate at idle. the highest it has ever gotten at idle is 85C, on a 100 degree F day with the AC on high.

also, i have NEVER seen 100 degrees C, including on the track in 100 degree heat.

as i said though, i run a drilled thermostat, which eliminates fluctuation, and flows the coolant though the system better which improves the heat dissipation, an 85/92 fan switch, a 50/50 mix of phosphate free coolant and distilled water, and a bottle of water wetter. this has been working perfectly in the blue car for 11 years, and the white car for the 4 years i've had it.
What you're experiencing is a faulty gauge then. The way the system is designed it is impossible to always hold the same temp when sitting still at idle. To do that would require an infinitely variable fan speed to tailor airflow to exactly the amount needed to stabilize radiator temperatures. Obviously, our cars do not have this.

Stopped, at idle, with no natural airflow, the thermostat, whether drilled or otherwise, does not control temperature. Period. End of story.

In those conditions, temperature is limited by the radiator's ability to shed heat, which is controlled by the radiator fans. It cannot shed heat fast enough to stop the temperature from rising just on its own. It needs airflow to do that. Until you get airflow, temperature will continue to rise because the system cannot rid itself of heat. And until the fans come on, there's no airflow. So until the temperature reaches at least the low-speed fan trigger point, the system temps will rise.

If you're running aftermarket oversized radiators or have otherwise significantly increased the capacity of the cooling system, then that will change things. But stock components absolutely will operate in exactly the manner I've described. To state otherwise is, frankly, stupid. It serves only to unnecessarily mislead other people.

My car has fresh coolant, a clear radiator, proper bleeding, 50/50 mix with distilled water and Pentofrost NF and a fully stock cooling system (including undertrays). It hovers around the low-speed fan temp when sitting still on most days and on really hot days will creep to the high-speed fan temp. Just as it is designed to do.

Also, turning the A/C on will lower coolant temps when sitting still in most cases because the A/C system will trigger the high speed fans due to high-side A/C pressures long before coolant temps reach the high-speed fan trigger point. This will keep radiator temperatures down by increasing airflow over the radiator and increasing heat dissipation.

Finally, on the track, you're moving. You won't see 100 degree temps while in motion because, wait for it, there is airflow over the radiator. Notice the recurring theme here? Once you're over about 20 mph you're flowing much more air over the radiator than the fans can ever hope to. On a track, at speed, even when driven hard, the temps will be lower than when sitting still for a properly functioning system (they should hover around the thermostat temp because at speed the radiator can shed heat faster than the engine can generate it and the thermostat will partially close until flow is reduced enough to equalize with the radiator's heat dissipation).

Overall, it's not clear that you actually understand that there's a difference between being in motion and sitting still or driving at below about 10 mph for long periods of time. You seem to be under the mistaken impression that the radiator sheds the same amount of heat at 80 mph as it does at 0 and that's just not true.
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Shifting is an art. Learn it, love it, live it.
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Silver 1998 Volvo S70 T5 <- Daily (Anja)
Guards Red 1986 951 <- Seattle car (Gretchen)
White 1976 914 2.0 F.I. <- Prodigal car, traded away then brought back again (Lorelei)

Last edited by AaronM; 08-16-2014 at 12:44 AM..
Old 08-16-2014, 12:12 AM
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Quote:
Originally Posted by pjo046 View Post
As my needle never gets above 100 C, I guess the high speed setting never kicks in on my fans. If I change from my stock 92/102 fan switch to a 85/92 fan switch, then I think that should actually solve the problem I have (As long as my oil temps aren't too high, which is really my main concern).

But, what are the draw backs with using the 85/92 fan switch? I assume the fans will be running at low speed more or less constantly since my thermostat is also set at 85 C?
The gauge isn't always perfectly accurate. You can hear the difference between high speed and low speed fans if you're outside of the car or have the windows down. It's very clear.

An easy way to trigger the high-speed fans is to run the A/C. The high speed fans are also triggered by A/C system pressures (they kick on at around 200 PSI high-side in my car) regardless of coolant temp at the radiator. It will typically take 5-15 minutes of A/C operation with the car at a standstill for this to happen at about 80 degrees ambient. Then you can at least hear the difference with the high-speed fans.

The potential downside to running a lower-temp fan switch is exactly as you describe. You run the risk of having a setup where the fans operate all the time. This can actually slightly reduce airflow at highway speeds by inducing extra turbulence behind the radiator. It's also not particularly good for the fan motors in terms of expected lifespan. In practice, with a decently clean stock radiator there is so much extra airflow over the radiator at speed that there should be no need to worry about the turbulence.

The reason that most cars have the radiator fans come on a temps above the thermostat set point is to ensure that the fans are off when the car is in motion.

When you are at speed the fans are not needed and many dedicated racing cars do without the fans entirely (though they obviously then have to be very careful about how much time they spend operating at low speeds in the paddock since removing the fans makes the car susceptible to overheating unless it's moving at over 15-25 mph).

Ideally, you will want to match the low-temp fan switch with a low-temp thermostat as well.
__________________
Shifting is an art. Learn it, love it, live it.
---------
Silver 1998 Volvo S70 T5 <- Daily (Anja)
Guards Red 1986 951 <- Seattle car (Gretchen)
White 1976 914 2.0 F.I. <- Prodigal car, traded away then brought back again (Lorelei)
Old 08-16-2014, 12:41 AM
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Thank you for very informative posts! :-)

I don't have A/C on mine, so can't check for proper high speed operation that way. But I will follow the test-intstructions on Clark's Garage to check for proper operation of the temp switch and fan relay.

Running a lower temp switch is out of the question then, as I won't run a lower than stock setting on the tstat. That would make the engine run below its intendend operating range, and impair combustion efficiency.
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- 1972 Porsche 911, rebuilt to '76 Carrera 3.0 spec
- 1986 Porsche 944 Turbo
Old 08-16-2014, 05:35 AM
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aaron - sorry - what you are describing would only happen in a stock system, due to the fans coming on AFTER the thermostat opens. this would inherently create a cycling effect. with the fans coming on at the same time as the thermostat opening, this is not an issue.

i've checked the gauge with both a laser thermometer, and the durametric. all agree on the temp. my radiator is stock in both cars, as well as all of the cars i am talking about. i have paid particular attention to this issue, as a part of the developement and implementation of the supercharger project. one of the things we were all worried about was operating temps. it did not change one bit, and if anything, actually runs cooler. the idle temp is rock solid and never gets above 85C, no matter how hot it is outside. the fans kick in at 85C and bring the temp back down to 80 in less than a minute. the needle moves less than a needle's width during the entire process.

perhaps you do not understand the concept of how a radiator system works. the coolant STOPS in the tank and cools off. it does not continue to flow all the time. then the thermostat opens after the coolant on the engine side gets too warm, and lets the cooler liquid into the engine.

a drilled thermostat allows a small amount of coolant to pass at all times. this allows a more even exchange of heat through the radiator, and the mere nature of flowing through the system dissipates heat better. during the winter my fans don't come on at idle at all. in fact, it's a royal pain to try to bleed a system in the winter, as i have a hard time getting it up to temp at idle.

i would be happy to show you how it works. most of us running 968s now run at least the low temp fan switch, and many of us are now running a drilled thermostat. we all experience pretty much the same thing. i could put you in touch with a couple hundred of them. our engines create more heat than the 944 too, so the system has to work harder. we do run the same 951 radiator (stock for the 968), and i'm not sure what the 944 runs. perhaps that is the reason it works. perhaps the basic 944 has a smaller radiator.

Last edited by flash968; 08-16-2014 at 07:14 AM..
Old 08-16-2014, 07:10 AM
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Quote:
Originally Posted by flash968 View Post
yup - both 968s. one supercharged, and one normal.

I am sincerely envious. I sometimes mistake the coolant gauge for the tach!
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Old 08-16-2014, 07:35 AM
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lol - ouch!!!

that is actually one of the beautiful things about the SC. no longer revving to the end really helps bring down the temps. there is so much power now, that there just isn't any need. i can't remember the last time i went over 6k rpm.

that's another thing that many people forget about. most performance chips add timing advance. that increases temps quite a bit. just running around at 4k rpm will raise temps enough to see it on the gauge.

the big one though is the belly pans. deleting those can easily raise operating temps 5 to 10 degrees C.
Old 08-16-2014, 08:35 AM
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Quote:
Originally Posted by flash968 View Post
aaron - sorry - what you are describing would only happen in a stock system
The OP has a stock system and I have repeatedly made it clear that I'm describing the appropriate stock behavior. This is not a difficult concept.

Quote:
Originally Posted by flash968 View Post
due to the fans coming on AFTER the thermostat opens. this would inherently create a cycling effect. with the fans coming on at the same time as the thermostat opening, this is not an issue.
You claim to have an 85 degree fan switch yet claim to run 80 degree coolant temps even when stationary. If those numbers are true, your fans should never be coming on at all.

Now you're claiming that the fans come on when the thermostat begins to open.

Which is it?

Quote:
Originally Posted by flash968 View Post
the fans kick in at 85C and bring the temp back down to 80 in less than a minute. the needle moves less than a needle's width during the entire process.
So your temperature does, in fact, oscillate around the fan on/off point. This is exactly what I've been saying will happen. You are agreeing with me.

Quote:
Originally Posted by flash968 View Post
perhaps you do not understand the concept of how a radiator system works. the coolant STOPS in the tank and cools off. it does not continue to flow all the time. then the thermostat opens after the coolant on the engine side gets too warm, and lets the cooler liquid into the engine.
This is just wrong. The thermostat does not fully close in normal operation. As you yourself have said, the thermostat is not a switch; it does not pop open instantly at the set temp and does not pop closed below the set temp. Rather, it begins opening about 10 degrees below the set temp and does not become open until the set temp has been reached.

In situations where the radiator is dissipating more heat than the engine is putting into the coolant, the thermostat will begin to close and will thereby restrict the flow of coolant into the radiator, reducing the heat dissipated. However, the thermostat should not close completely. Unless the cooling system is truly excessive, what will happen is that temperatures will stabilize at a point where the thermostat is partially open (which is below its rated temperature). If the thermostat closes completely when the engine is running, the cooling system is oversized for the conditions and a portion of the radiator should be blanked off (as is done for semi trucks in winter).

An 85 degree thermostat should begin to open at about 75 degrees. If your thermostat were closing completely, your coolant temps would be dropping down to 75 degrees, not remaining steady at 80. At 80 degrees, an "85 degree" thermostat will be partially open even if not drilled and will absolutely be allowing some amount of flow through the radiator (though it would not be allowing full flow).

Quote:
Originally Posted by flash968 View Post
a drilled thermostat allows a small amount of coolant to pass at all times. this allows a more even exchange of heat through the radiator, and the mere nature of flowing through the system dissipates heat better. during the winter my fans don't come on at idle at all. in fact, it's a royal pain to try to bleed a system in the winter, as i have a hard time getting it up to temp at idle.
This is not a good thing. This is indicative of a cooling system will too much capacity and during the winter it sounds as though you need to blank off at least a portion of the radiator to prevent damage from the engine running too cold. Also, the chief reason for a drilled thermostat is to prevent the formation of air bubbles behind the thermostat and make it easier to bleed the system. Once the engine is at operating temperature where the thermostat is always at least partially open, the drilling makes no difference.
__________________
Shifting is an art. Learn it, love it, live it.
---------
Silver 1998 Volvo S70 T5 <- Daily (Anja)
Guards Red 1986 951 <- Seattle car (Gretchen)
White 1976 914 2.0 F.I. <- Prodigal car, traded away then brought back again (Lorelei)

Last edited by AaronM; 08-16-2014 at 10:30 AM..
Old 08-16-2014, 10:16 AM
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wow

you said it was impossible. i said here is how it is possible.

what my system does, as with any system, is dependent on the ambient temp.

technically my temps oscillate at idle, but it is so small that the needle doesn't always show it. it's not more than 5C from one extreme to the other at idle (less than the width of the needle). my fans do not always come on. it has to be about 70 degrees F outside for them to come on at idle. below that, they don't come on. it just runs that cool.

running down the road with ambient temps above 70F, it sits dead smack at 85C and never moves. if it is below 65F ambient, then it sits smack at 80C. if i run the AC, it pushes it up a touch, but not quite to 90C. really hotdogging around, it can get up to 95C, but has never reached 100C.

drilling a thermostat is an OLD racer's trick. it makes the cooling system fluctuate less, which is what you want. fluctuation is very bad for longevity of things like head gaskets.

i have definitely had my thermostat close fully while driving. it happens all the time in the winter. fortunately i have a drilled thermostat, which allows a little bit of flow, and prevents the temp swing as it opens and closes. this does make my heater less potent though.

clearly my system works better than stock. so do the 50 other supercharged cars out there, as well as the hundreds of us who have changed the fan switch and/or drilled the thermostat. we've all been doing it for years. again, i would be happy to put you in touch with them.
Old 08-16-2014, 11:00 AM
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Quote:
Originally Posted by flash968 View Post
you said it was impossible. i said here is how it is possible.
No, you haven't. You've shown no evidence to suggest that zero oscillation happens consistently over all temps when stationary, which was what your initial claim stated.

Quote:
Originally Posted by flash968 View Post
technically my temps oscillate at idle
Which proves I was correct and that your earlier statements were misleading. All I was saying is that the system will hover between the fan on/off points when stationary because the fans aren't infinitely variable and cannot precisely match airflow to hit an exact heat dissipation balance all the time.

Quote:
Originally Posted by flash968 View Post
my fans do not always come on. it has to be about 70 degrees F outside for them to come on at idle. below that, they don't come on. it just runs that cool.
Then it is over-cooling and you have too much capacity. This will cause problems in cold weather. That may not be an issue for you in CA, but for those of us with four seasons who run the car often when temps are in the 40s or below, that would cause issues.

Quote:
Originally Posted by flash968 View Post
running down the road...
Is completely irrelevant. We're not talking about temperatures at speed. We're talking about temperatures when stationary. All your discussion about temperatures at speed does is further distract from the actual topic. Your "information" is more likely to confuse a novice than to educate them.

Quote:
Originally Posted by flash968 View Post
drilling a thermostat is an OLD racer's trick. it makes the cooling system fluctuate less, which is what you want.
Yes, it is an old racer's trick. So are many other things that don't necessarily work.

The drilling is to create a means for trapped air to pass through the thermostat to ease the venting of the system. It is typically done with a single very small hole (usually 3/32 or smaller) and despite folk wisdom does not actually reduce fluctuation unless the cooling system is so massively over-capacity that the thermostat is closing during operation, which is a fault that requires repair, not a beneficial feature.

Quote:
Originally Posted by flash968 View Post
fluctuation is very bad for longevity of things like head gaskets.
Rapid fluctuations outside of the design limits are bad. The expected slow changes caused by a stock system operating within design parameters are not. There is a difference.

Quote:
Originally Posted by flash968 View Post
i have definitely had my thermostat close fully while driving. it happens all the time in the winter.
Again, this is a fault, not a feature. If your thermostat is fully closing, it means that you are seeing temps below 75 C (assuming a stock thermostat) which is not ideal for street driving.

Quote:
Originally Posted by flash968 View Post
clearly my system works better than stock. so do the 50 other supercharged cars out there, as well as the hundreds of us who have changed the fan switch and/or drilled the thermostat. we've all been doing it for years. again, i would be happy to put you in touch with them.
Something that works and something that is optimal are very different things. I have no doubt that your setup works. What it is not, however, is optimal in cold weather. I am certain that it is great for high-temp track days, but it is not suited to road cars that are driven year-round based on your description of the temperatures you see.

You have a system set up to work well on hot days at the track. That's fine if that's how the car is used. But it's not optimal for cold, or even cool, weather use on a street car. The fact that it's not optimal doesn't mean it will cause rapid failure, but it does mean that it's not something to point to as how the car "should" behave.

When someone with a stock car asks how it should behave and you come in with your "information" about a decidedly non-stock setup, you do not help anyone. You only confuse the topic and spread misinformation about how the stock system works.

If you prefaced your posts with "I have a modified cooling system and what I experience is not accurate for a stock system" I would probably not take issue. But you don't do that. You make it sound as though your experiences are how the stock system should work and that's just plain wrong.
__________________
Shifting is an art. Learn it, love it, live it.
---------
Silver 1998 Volvo S70 T5 <- Daily (Anja)
Guards Red 1986 951 <- Seattle car (Gretchen)
White 1976 914 2.0 F.I. <- Prodigal car, traded away then brought back again (Lorelei)
Old 08-16-2014, 12:10 PM
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for all intents and purposes, my temp is rock solid at idle, and in fact, at ambient temps below 65F it does not move at all. so, yes, it is possible. i would be happy to show you.

it is not over cooling or have too high a capacity. the capacity is bone stock. it is just right for street driving. it is actually a bit small were i to want to track the car. a properly designed system would have no variance in operating temp under any conditions, including track i have merely found a combination that provided the smallest swing in temps.

the drilling is NOT for the purpose of air. it is for the purpose of allowing a small coolant to bypass the thermostat. the fact that it helps in the bleeding process is just an added bonus. as somebody who has been setting up cars professionally, and have owned a shop, i've been drilling thermostats for over 30 years, and mostly on cars that did not need or even have the ability to be bled. the drilling is not one small hole. on this car, i run 6 holes. on others i have run less, on still others i have run more. it all depends on the car and its system.

the only potential downside of this setup is that i am probably not burning the fuel as completely as i could, when it is cold outside. but, even here in southern california, it had no effect on emissions testing that i have done, and in fact had no effect when i got the CARB certification for the supercharger kit.

i don't track the car. i have no idea why you keep going there. this is a street setup.

i think everyone should be running a low temp fan switch. anybody in a climate that doesn't dip below about 45F should be running a drilled thermostat. the stock system sucks. it allows too much variance in operating temp under arduous conditions. this has led to countless failures and problems.

i can easily put you in touch with hundreds of owners who feel exactly the same way, for exactly the same reasons.

also, i have checked a number of gauges in these cars, and they don't generally read accurately, but in fact read high.

all that being said, perhaps the difference is the radiator itself. the 951 radiator seems perfectly capable of sustaining stable temps, when used with a low temp fan switch (hundreds of cars to prove it).

perhaps the difference is that the 968 runs an oil cooler.

perhaps the dual speed dual fans are different.
Old 08-16-2014, 01:48 PM
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Quote:
Originally Posted by flash968 View Post
for all intents and purposes, my temp is rock solid at idle
Quote:
Originally Posted by flash968 View Post
the fans kick in at 85C and bring the temp back down to 80
Those statements cannot simultaneously be true. One or the other must be false. Which is it?

Quote:
Originally Posted by flash968 View Post
at ambient temps below 65F it does not move at all
Considering that the OP's question is dealing with summer temperatures and conditions, that's not really relevant to the discussion.

Quote:
Originally Posted by flash968 View Post
it is not over cooling or have too high a capacity. the capacity is bone stock.
A bone stock system would not have problems getting up to temp in cold weather. I've driven various models of these cars for well over a decade and they've all come up to operating temp just fine even in 20 degree Fahrenheit weather.

Quote:
Originally Posted by flash968 View Post
a properly designed system would have no variance in operating temp under any conditions, including track
What is with your hard-on for zero variance? It's unrealistic and misleading to people who are trying to understand how cooling systems work. Even the multi-million-dollar cooling systems on Formula 1 cars experience coolant temperature variations as conditions change.

Quote:
Originally Posted by flash968 View Post
the drilling is NOT for the purpose of air. it is for the purpose of allowing a small coolant to bypass the thermostat. the fact that it helps in the bleeding process is just an added bonus. as somebody who has been setting up cars professionally, and have owned a shop, i've been drilling thermostats for over 30 years, and mostly on cars that did not need or even have the ability to be bled. the drilling is not one small hole. on this car, i run 6 holes. on others i have run less, on still others i have run more. it all depends on the car and its system.
Lots of people believe what you've just said. But lots of people also believe that removing the undertrays helps airflow.

The thermostat exists not to set a maximum temperature for the engine, but rather to set a minimum temperature. Drilling holes in the thermostat reduces or eliminates the thermostat's ability to do its job of maintaining the engine's minimum temperature.

The fans control the engine's maximum temperature.

Both systems have a range where they're operating (the ~10 degree C range between fully open and fully closed for the thermostat and the range between the on and off points for the fans) and it's important not to have these ranges overlapping. If the ranges overlap, you have the thermostat trying to heat the engine and the fans trying to cool the engine at the same time.

One of the best explanations I've seen was on a Corvette board: I'm renaming the thermostat. - Corvette Forum

Drilling a thermostat to the extent you descripe is a cheap, crude, and completely improper way of lowering the engine's minimum temperature.

Quote:
Originally Posted by flash968 View Post
i don't track the car. i have no idea why you keep going there. this is a street setup.
I keep going there because that's the only place your setup should be used. You may market it as a street setup, but given that you yourself have admitted that it cannot get up to operating temp in cold conditions it's obviously not suitable for someone who drives their car year round in any place that gets anything close to winter.

Quote:
Originally Posted by flash968 View Post
i think everyone should be running a low temp fan switch.
Not unless they are also running a lower temp thermostat. The fans should never come on unless the thermostat is fully and completely open.

Quote:
Originally Posted by flash968 View Post
anybody in a climate that doesn't dip below about 45F should be running a drilled thermostat.
Just no. A drilled thermostat has no ability to effectively set a minimum engine temperature and cannot fully do its job. A lower-temp thermostat may be a good option for high temperature environments, but a drilled thermostat is not.

Quote:
Originally Posted by flash968 View Post
the stock system sucks. it allows too much variance in operating temp under arduous conditions. this has led to countless failures and problems.
Which is why these cars routinely run 200,000 or 300,000 miles without heat issues.

The only problem with the stock system is that people are no longer used to seeing temperature gauges that rise and fall in sync with the radiator fans as was normal many decades ago and get excessively antsy when they see the gauge moving in their 944.

Quote:
Originally Posted by flash968 View Post
i can easily put you in touch with hundreds of owners who feel exactly the same way, for exactly the same reasons.
And I can put you in touch with thousands of people who believe vaccines cause autism. That doesn't make them right.

The bottom line is this:

The cooling fans should never come on unless the thermostat is completely open. If you go to a low-temp fan switch, you should also have a lower-temp thermostat. Otherwise you can have the fans running excessively which is less than ideal.
__________________
Shifting is an art. Learn it, love it, live it.
---------
Silver 1998 Volvo S70 T5 <- Daily (Anja)
Guards Red 1986 951 <- Seattle car (Gretchen)
White 1976 914 2.0 F.I. <- Prodigal car, traded away then brought back again (Lorelei)
Old 08-20-2014, 10:58 AM
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all new cars have rock solid operating temps. they don't move at all. explain that one. it's not the gauge either. it's the fact that the system is properly designed.

the reason that older cars used to fluctuate was poor airflow management. most cars didn't even have a fan shroud until well into the late 70s. none of them had belly pans. now they all have both. this is the key. belly pans REDUCE operating temps because they increase the negative pressure zone behind the radiator. anybody who think otherwise probably also denies global warming. you do not want more air under the hood. you want less. you want ALL of the air that gets in there to have to pass over the radiator first, and then exit smoothly. this is basic fluid dynamics, and taught in your first year of engineering in college.

i have been doing this professionally for over 30 years. i can say with confidence that i can make every one of these cars run with a stable operating temp. there is no reason that the needle should swing more than 10 degrees under any condition.

as for thermostats, frankly, if you need to run the normal fan switch, then the thermostat should be HIGHER not lower. porsche chose what they did to meet emissions standards. it was not to have the best and most efficient system.

i just drove my car. it was 75 degrees out. my fans did not come on at all. the temp sat at just over 80C the entire time. supercharger fluid temp was at 5 degrees above ambient. just like always. not one movement of the coolant temp. there never really is.

it is clear to me that you really don't understand how a cooling system works, so i really don't feel that this discussion is productive.

anybody who wants their car to run cooler can contact me. i will be happy to give further details on what to do to stop the ridiculous behavior of the stock system. i have a 100% success rate on this. you can read about countless people who have the same experience over on 968forums.com. we all know he real deal, and have moved on from the provincial thinking that porsche knew everything.

Last edited by flash968; 08-20-2014 at 12:20 PM..
Old 08-20-2014, 12:17 PM
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Quote:
Originally Posted by AaronM View Post
What you're experiencing is a faulty gauge then. The way the system is designed it is impossible to always hold the same temp when sitting still at idle. To do that would require an infinitely variable fan speed to tailor airflow to exactly the amount needed to stabilize radiator temperatures. Obviously, our cars do not have this.

Stopped, at idle, with no natural airflow, the thermostat, whether drilled or otherwise, does not control temperature. Period. End of story.

In those conditions, temperature is limited by the radiator's ability to shed heat, which is controlled by the radiator fans. It cannot shed heat fast enough to stop the temperature from rising just on its own. It needs airflow to do that. Until you get airflow, temperature will continue to rise because the system cannot rid itself of heat. And until the fans come on, there's no airflow. So until the temperature reaches at least the low-speed fan trigger point, the system temps will rise.

If you're running aftermarket oversized radiators or have otherwise significantly increased the capacity of the cooling system, then that will change things. But stock components absolutely will operate in exactly the manner I've described. To state otherwise is, frankly, stupid. It serves only to unnecessarily mislead other people.

My car has fresh coolant, a clear radiator, proper bleeding, 50/50 mix with distilled water and Pentofrost NF and a fully stock cooling system (including undertrays). It hovers around the low-speed fan temp when sitting still on most days and on really hot days will creep to the high-speed fan temp. Just as it is designed to do.

Also, turning the A/C on will lower coolant temps when sitting still in most cases because the A/C system will trigger the high speed fans due to high-side A/C pressures long before coolant temps reach the high-speed fan trigger point. This will keep radiator temperatures down by increasing airflow over the radiator and increasing heat dissipation.

Finally, on the track, you're moving. You won't see 100 degree temps while in motion because, wait for it, there is airflow over the radiator. Notice the recurring theme here? Once you're over about 20 mph you're flowing much more air over the radiator than the fans can ever hope to. On a track, at speed, even when driven hard, the temps will be lower than when sitting still for a properly functioning system (they should hover around the thermostat temp because at speed the radiator can shed heat faster than the engine can generate it and the thermostat will partially close until flow is reduced enough to equalize with the radiator's heat dissipation).

Overall, it's not clear that you actually understand that there's a difference between being in motion and sitting still or driving at below about 10 mph for long periods of time. You seem to be under the mistaken impression that the radiator sheds the same amount of heat at 80 mph as it does at 0 and that's just not true.
this post is correct.

i too have a 85/92 fan switch, stock cooling otherwise, new water-pump, radiator, tank, thermostats and new coolant in the last 3 months.

and at idle, the temp will creep up to the low fan speed. this is because at idle the engine is generating more heat than the radiator can expel without forced air motion (natural convection). so the coolant temp will rise to when the fans come on, and the fans will force air over the radiator, and cool the coolant back off.

this is normal operation of the coolant system.

idling in high heat is the toughest condition you can put on your cooling system, besides maybe after hot running, turning it off.

whenever you are traveling at almost any speed at all, this will be sufficient to cool the engine.
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Old 08-20-2014, 12:43 PM
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i just did another errand run around town. 80F outside now. stop and go for 30 minutes. needle never got above 85C and sat between 80 and 85 (basically needle dead on the lower line and then the bottom of the needle at the lower line with the rest of the needle sitting on top of it). fans came on twice for a few seconds each time, and both times right after i started the car after stopping for an errand.

both of my 968s behave the same way, as do all of the ones i help set up. nothing magical here. just choosing the right combination of components, coolant, distilled water, and water wetter, and making sure no extraneous air gets into the engine bay. it works. i don't know what else to say, so i'll now step out of this.

everybody knows how to reach me when they get tired of watching the needle dance around and flirting with 100C
Old 08-20-2014, 01:36 PM
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Quote:
Originally Posted by flash968 View Post
i just did another errand run around town. 80F outside now. stop and go for 30 minutes. needle never got above 85C and sat between 80 and 85 (basically needle dead on the lower line and then the bottom of the needle at the lower line with the rest of the needle sitting on top of it). fans came on twice for a few seconds each time, and both times right after i started the car after stopping for an errand.

both of my 968s behave the same way, as do all of the ones i help set up. nothing magical here. just choosing the right combination of components, coolant, distilled water, and water wetter, and making sure no extraneous air gets into the engine bay. it works. i don't know what else to say, so i'll now step out of this.

everybody knows how to reach me when they get tired of watching the needle dance around and flirting with 100C
this is not what you said at the start of the thread, and confirms that me and aaron are correct.
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Old 08-20-2014, 01:48 PM
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i should clarify that when the needle got to 85, it was after stopping the car. it went right back down the instant i fired it up. idle never got above 80C. needle barely moved at all.

all of our 968s in the group run the same way. there are hundreds of us. maybe we're just onto something that the 944 guys haven't figured out yet. whatever. it works.
Old 08-20-2014, 01:52 PM
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Quote:
Originally Posted by flash968 View Post
i should clarify that when the needle got to 85, it was after stopping the car. it went right back down the instant i fired it up. idle never got above 80C. needle barely moved at all.

all of our 968s in the group run the same way. there are hundreds of us. maybe we're just onto something that the 944 guys haven't figured out yet. whatever. it works.
now you are back to an impossible story.

either the coolant goes up in temp to the fan temp and then cools off when the fans come on, or its doesn't. the second alternative is impossible, literally physically impossible.
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Old 08-22-2014, 01:51 PM
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in really looking at the gauge, a needle's width is really about 3 degrees and not 5, so i am really sitting between 80 and 81.5 at idle.

it bumps up to about 85 after i shut it off. upon starting, things start flowing again, fans still not on, and within a few seconds, it drops back down to 80 or so. i attribute this to the holes i have drilled. it allows more coolant to pass than just the thermostat.

this does not change, until the ambient temp gets up a bit (over 80F). then the fans come on and off once in a while as i am sitting in traffic.

it's really very stable. i attribute a lot of this to the water wetter. it makes for better heat transfer. this means that the radiator does a better job without the fans having to come on. the 30 or so cars i've had through here are the same. the hundreds of them who have followed this setup are also the same.

again, not sure what's different about the 944, but it sure works on the 968. it has worked on every other car i've ever had too.

the other added benefit of drilling the thermostat is that if your thermostat sticks, you will still have flow. it makes it much harder to boil over.

the downside is longer warmup periods. in cold climates this could present an issue if you are in a hurry. it can also confuse the ECU and keep in it open loop longer, thereby costing you some fuel until it warms up.

many thermostats already have a hole in them for exactly these reasons.

there are countless sites and threads about the benefits of doing this. i encourage everyone to do some reading. here are just a few:

https://www.easyperformance.com/support/technology-reports/thermostat-replacement-testing

Why Drill Holes in your Thermostat? | ZZP News

Thermostat modification options
Old 08-22-2014, 03:11 PM
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To prove you are/are not full of ****, put a go pro on you dash to record the temp gauge with ODO in view. Drive around for thirty minutes. If you don't have a go pro, buy one, I do recall you spend more money on wine than any of us make a year.

Prove us wrong.
Old 08-22-2014, 05:38 PM
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