High coolant temps when car is stationary

[pjo046]

I have a rebuilt engine with new waterpump, thermostat, new coolant hoses, new aluminium radiator and I have used Evans Waterless coolant (Powercool 180).

When I am driving the car around at normal speeds the coolant temp reading on the gauge is more or less spot on center where it should be (90 degrees Celcius/194 deg Fahrenheit). When driving slowly or standing still, the temperature increases. If I let the engine idle for a long time when the car is stationary, the needle stops rising at just below the 100 degree celsius mark. So it is probably at about 98-99 degrees celsius.

I have checked that the radiator fans kick in as they should (stage 1, low speed).

What are the possible causes for this "over heating"? I never had this problem before my engine rebuild. The temp would always stay steady at 90 C, regardless of ambient temperatures, driving habits etc.

I know Evans coolant hasn't got as high heat capacity as regular coolant/water-mixes. And Evans states that on some cars the operating temp can go slightly up with Evans as opposed to regular coolant. But if so, shouldn't the temps be higher at all times?

I have searched a lot with regards to the Evans Coolant, but have not found any other 944 owners using Evans who has reported it resulting in higher coolant operating temps.

IF Evans is the cause, I will change back to regular coolant as I do not want increased coolant temps (As that will lead to higher oil temps and thinner oil --> More prone to rod bearing problems etc). However, once Evans has been drained and the system filled with normal coolant and water, I can't reverse the operation without buying some very expensive prep fluid before refilling Evans. Therefore I want to pursue all other possible causes for my problem before removing the Evans coolant.

[CHICKS]

Anywhere between the two center marks is normal. Unlike most new cars, the gauge will move when the temperature changes. Notice new car gauges (if they have one) just rise to the operating temp and don't move? It's so people don't freak out when they see the temps all over the place (which is normal).

Sensors and Gauges - Information, Troubleshooting, and Testing

[pjo046]

Still it didn't happen before though. And it is not so much that it is moving about, more slowly increasing untill a higher steady state temp than earlier. A higher coolant temp will also cause higher oil temps and thus thinner oil --> more chance of nr2 rod bearing failures etc.

So I would really like to bring it back down to 80. Thats how the system is designed to work, with the thermostat opening and closing, the fans kicking in and going off again. Should be possible to keep a fairly stable running temp with those aids.

Of course, I know such a small temp increase isn't outright dangerous, but with regards to oil temps getting a bit higher also, it might impare the longevity of the engine, and in worst case cause a problem at track days. Or?

Correction: When looking at your picture (Which shows Celcius), I see that I typed wrong temperatures in my first post. I meant my temps are at 90 degrees (Middle of gauge) when driving, and 98-99 when stationary. So they are in the upper range of the "normal" temperature range.

[v2rocket_aka944]

which thermostat did you put in when you replaced it? perhaps you had the low temp tstat before and replaced with a high temp?
or your fan switch is the high temp version?

[flash968]

do both fans kick in? do they come on at both the high and low points?

[pjo046]

As far as I could see, both fans kicked in. I haven't tested manually overriding them to check if both high and low settings work. Do the 1986 944T have two fan speeds, or is that only on later models?

I put in a regular thermostat. If I had the low temp tstat before, shouldn't I get lower than normal coolant readings? Instead of spot on 90 degrees both on standstill, coasting, highway cruising and spirited driving?

Are there different versions of fan switches out there? I didn't know. I do believe however that the fan switch was reused during the rebuild, thus it's the same unit as before.

[cockerpunk]

sounds normal to me.

[amehl]

Originally Posted by pjo046

As far as I could see, both fans kicked in.

Mine was doing something similar where the fan would kick in late, only getting hot in traffic. A new $13 fan switch (low-temp) fixed that.

[AaronM]

Originally Posted by pjo046

So I would really like to bring it back down to 80. Thats how the system is designed to work, with the thermostat opening and closing, the fans kicking in and going off again. Should be possible to keep a fairly stable running temp with those aids.

It is not possible to have the temperature sit at a steady 80 degrees centigrade with the car sitting still at idle.

The low-speed fans don't come on until 92 degrees centigrade and the high-speed fans don't come on until 102 degrees centigrade. In both cases, however, with our later cars, both fans should run at both speeds.

Without airflow on warm days the radiator cannot shed enough heat to stop the coolant temps from rising without the fans on. So the minimum temp on a warm day would hover around 92 degrees with the low-speed circuit on. Even if the thermostat is fully open, the coolant temp will be dictated by the amount of heat the radiator can dissipate.

On hot days with the car sitting still it is perfectly normal for the the coolant temp to oscillate slowly between 102 degrees centigrade (where the high-speed fans come on) and the mid-90s centigrade (where the high-speed fans turn off).

If you have lower-temp fan switches, you can set these values lower, but with the stock switches, your car is behaving as designed.

[flash968]

both of my cars sit solid at the 80 mark at idle, regardless of anything else. it does not fluctuate whatsoever. but i also have an 85/92 fan switch, and run 50/50 coolant with a bottle of water wetter, as well as a drilled thermostat.

[DannoXYZ]

I put in a regular thermostat. If I had the low temp tstat before, shouldn't I get lower than normal coolant readings? Instead of spot on 90 degrees both on standstill, coasting, highway cruising and spirited driving

Thermostat-temp only affects warm-up time. Once fully warmed up, both thermostats are fully opened and will not affect steady-state temperatures since that's highe than either thermostat. People will mistakenly notice lower temps when replacing thermostat an attribute it to the change in opening-temp. But the real change was due to replacing a defective clogged thermostat with a working one.

In your case, do you burp the cooling system after changing thermostat and coolant?

Do both of the cooling fans tun on when the gauge gets to the upper end?

[flash968]

not true. the thermostat actually moves quite a lot during operation. it is a very common misconception that it opens and closes like a switch. that coil expands and contracts a lot during operation, and moves fairly slowly. it is designed that way specifically to partially close when it cools down a bit, and then slow down the coolant and prevent wide swings in temp due to sudden changes in temp. that's exactly why i drill my thermostats. it further helps maintain an even temp by allowing a small amount of coolant to pass all of the time.

any air in the system and you can easily have a fluctuating gauge. bleeding the system is actually somewhat involved. not only do you need to have the coolant temp up to operating temp, but you also have to have the heat on full, and the heater fan on high. it also helps to have the nose of the car slightly higher than the tail, to promote the air going to the highest point.

[DannoXYZ]

But at the upper end of the thermostat's range, shouldn't it be fully open? In the OP's case, his lowest operating temp after warm-up is above the upper end of any thermostat, stock or low-temp.

[flash968]

yes - it should. the thermostat should not be fully open at 80C but it should be fully open before 90C (a stock thermostat is 85C) that puts the needle a bit above the 80 mark, but less than half way to the 100 mark. if the needle is or was behaving differently, then perhaps it is or was the gauge. i would check it with a laser thermometer.

also, are the belly pans in place? these really help the cooling system by blocking extraneous air entering the engine bay and by promoting the negative pressure zone behind the radiator.

side note: generally cooling systems should run about 100 degrees above ambient, or 10-15 degrees above the thermostat point, whichever is higher.

p.s. - gasoline burns best when the coolant temp is above 195 degrees. that is why all new cars have their systems set so that the coolant is about 200-210. if the temp is too low, it won't burn fully.

[curtisr]

Originally Posted by flash968

both of my cars sit solid at the 80 mark at idle, regardless of anything else. it does not fluctuate whatsoever. but i also have an 85/92 fan switch, and run 50/50 coolant with a bottle of water wetter, as well as a drilled thermostat.

And this is a Porsche?!

[flash968]

yup - both 968s. one supercharged, and one normal.

[DannoXYZ]

Originally Posted by flash968

p.s. - gasoline burns best when the coolant temp is above 195 degrees. that is why all new cars have their systems set so that the coolant is about 200-210. if the temp is too low, it won't burn fully.

Also needs to be hotter than water's boiling point to boil off all the condensation in the crankcase and oil.

The hotter the engine runs, the more efficient it is at extracting expansion-energy out of the combustion. Less heat goes out into the water-cooling jacket heating up coolant and more heat is retained in the combustion-chamber to push down the pistons. The reason we have 200-degree engine is for durability reasons, plastics, rubber and aluminium can only deal with so much. Also hot-spots and pre-ignition/detonation.

Some very interesting research is being done on coolant-less engines with ceramics instead of metals. Much more energy is extracted from the combustion and you have less thermal-losses to the surroundings. Similar to ceramic-coatings on top of pistons and head. But for the entire engine.

[AaronM]

Originally Posted by flash968

both of my cars sit solid at the 80 mark at idle, regardless of anything else. it does not fluctuate whatsoever. but i also have an 85/92 fan switch, and run 50/50 coolant with a bottle of water wetter, as well as a drilled thermostat.

So, with no airflow (since the fans don't even come on at low speed until 85 degrees in your car), you're claiming the stock radiator can shed enough heat to keep the temperature at a steady 80? If so, you're full of -- well, something.

The stock radiator, with no airflow over it, simply cannot dissipate that amount of heat without airflow. At best you should see temperatures hovering around 85 degrees as the low-speed fans come on and off. Even in the middle of winter the radiator can't dissipate enough heat with no airflow to stop the temperature from creeping up slowly.

The simple truth is that the radiator needs airflow in order to shed enough heat to keep the temperature stable and that means that, when the car is sitting still, heat will always build at least until the low-speed fans come on. Period. If the gauge never moves from 80 degrees even when the car is sitting still for several minutes, then the gauge is broken.

When sitting still, the thermostat does not control temperature. When sitting still, the radiator fans control the temperature. When not moving, the system will always oscillate around the fans' on/off points, either at the low-speed on/off points for cooler days or the high-speed on/off points for hot days.

For a car with the stock thermoswitches for the fans, this means that, on most days, the coolant temp when sitting still will hover around 92 degrees and on very hot days will creep up to 102 degrees before falling again when the high-speed fans are triggered.

[flash968]

danny - yeah - you're right about it being more efficient. there is a paper from EPA or something out there that explains the reasoning for the 200 plus temps, which is to reduce emissions by burning the fuel more completely. it has been a while since i read it, but it's floating around and i'm sure somebody can find it.

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.

[pjo046]

I don't know how familiar you guys are with Evans, but it has several advantages over coolant containing water. The main advantages are less/no corrosion, lasts a lifetime, avoids hot spots in the engine due to water vaporization etc. It keeps the temperatures within the engine more stable which is important to avoid detonation caused by hot spots.

However, the main problem with Evans is that it is not as efficient in removing heat. That is it's heat capacity is much lower than water, and also a fair bit lower than 50/50 coolant/water. Thus if a cooling system is operating at it's limits, the steady state temps will go up when converting to Evans.

In my cooling system it seems like there is enough capacity built into the cooling system to keep the temperature where it should be (90 C) when the car is moving. Actually, the harder I drive (Higher RPM's) the more centered the needle will be. I assume this is because higher RPM's means higher coolant velocity.

But when I come to a stop, or slow driving, there seems to be a heat soak bringing temperatures up to just below 100 C. As all the components in my cooling system are new, I guess the most likely problem is the stock fans can't provide enough flow to cope with the reduced heat capacity of Evans.

Maybe I should try installing a pusher fan in front of the radiator, and wire it so that it kicks in at the same time the original fans kicks in with slow speed? I don't have A/C, so I have plenty of space in front of my radiator. My only concern with installing a pusher fan is that it may impair air flow and thus impair the fan-less cooling I get at speed.

BTW: Does anyone know what is the normal operating oil temperature in a 944 / 944T? I didn't have an oil temp gauge before I switched to Evans, so I don't know if my oil temp is too high or not. During normal and light spirited driving, my oil temp will go up to about 100 C. I think I have read somewhere that 70-90 C is within the normal range. So I am a bit worried that my oil temp is higher than normal, and that it is because the oil system needs to do more cooling since Evans has a lower heat capacity than regular coolant/water mixes.