oil temp question

[rnln]

at what temp would you alarm? I was sitting, stop and go, on freeway several days ago and oil temp craw up to 250 degrees. How bad is it?
Thanks.

[Joe Bob]

Not good....do you have an external cooler and a fan? If so, consider a manual over ride switch.

[Franks89-911]

I will probably sound like a broken record to some on here, but this pic is what I look at every time I see my needle creep up to midway and I get nervous.

So, if you're at 250C, you're getting into the "Too Hot!" range. Probably time to make a mod to fix that.

Cheers,
Frank

[rnln]

according to this pic, it was very close to 248 mark. My gauge doesn't have numbers
Do I have to change oil when it's at to 248 degrees? My oil is new.
Thanks guys

[997at]

My 82 SC gets to 250 if it's 90 degrees outside, I'm sitting in traffic, and the AC is on. Fortunately it doesn't get any higher than this and cools down quickly once I'm back up to normal road speed. Should I mod for this if it only happens once in a while?

[RichardNew]

The correct answer here is "It Depends"

The issue here is Shear Stability. Shear stability is a measure of the amount of viscosity an oil may lose during operation.

Are you running a synthetic or an old fashioned oil?

Mobil 1 synthetic is supposed to be capable of protecting engines “at well over 400 degrees F”. Most race cars have no problem running synthetics up to 290 degrees F But - they get nervous when a conventional oil exceeds 270 degrees F.

A NASCAR Sprint Cup engine runs about 220F but the World of Outlaws run as high as 300F.

Joe Gibbs Racing likes to point out that the cooler your oil is the lower the viscosity you can use. Drag racers are using 0w-5. NASCAR uses 10W-30 and WoO use 15W-50.

Now - back to the basics. The folks are Joe Gibbs told me a few years ago that if I had a question about oil just look in the owner's manual. Unless you have a $50,000 race engine the manual is the best source of information. That sort of makes it easy.

Richard Newton
Historic Racing Images

[997at]

Originally Posted by RichardNew

The correct answer here is "It Depends"

The issue here is Shear Stability. Shear stability is a measure of the amount of viscosity an oil may lose during operation.

Are you running a synthetic or an old fashioned oil?

Mobil 1 synthetic is supposed to be capable of protecting engines “at well over 400 degrees F”. Most race cars have no problem running synthetics up to 290 degrees F But - they get nervous when a conventional oil exceeds 270 degrees F.

A NASCAR Sprint Cup engine runs about 220F but the World of Outlaws run as high as 300F.

Joe Gibbs Racing likes to point out that the cooler your oil is the lower the viscosity you can use. Drag racers are using 0w-5. NASCAR uses 10W-30 and WoO use 15W-50.

Now - back to the basics. The folks are Joe Gibbs told me a few years ago that if I had a question about oil just look in the owner's manual. Unless you have a $50,000 race engine the manual is the best source of information. That sort of makes it easy.

Richard Newton
Historic Racing Images

Thanks for the great info. I'm running dino oil (Swepco 20/50W) because it has all of the extra minerals our old engines need. I'm not too worried about infrequent excursions in the 250 range……..seems to be somewhat expected and "normal" for the conditions. Here's a pic from a few weeks back here in CA. I was nervous as it kept climbing, but fortunately it stabilized at 250 and never went higher. Cooled down to 220 once traffic started moving again.

[Franks89-911]

RNLN, your gauge for your 87 does have numbers, they're really tiny and are printed on the extreme left edge of the gauge. You have to get all bendy in the car to see them in the gauge, but they are there. 60C, 90C, 120C, and 150C.

997AT's 82SC has an earlier gauge with no red zone but numbers throughout.

To RichardNew's point about the manual, pulling from my 89 manual (don't see how an 87 manual would be different RNLN) here's what it says about oil temp:

"If the needle enters the red field [302F/150C on my gauge and yours, RNLN, and I'm guessing yours too 997AT] you should slow down and, if the temperature still does not drop, contact a Porsche dealer immediately."


So I guess if we go "by the book" we don't really have to worry about an occasional creep-up even as high as 302F/150C, so long as it doesn't stay there? I wouldn't be too worried if I were you guys. It's hot out there and ambient temp has a lot to do with how hot the oil gets.

Anyway, hope that helps and stay out of the "red field"!

Cheers,
Frank

[J-Mac]

Quote
"Now - back to the basics. The folks are Joe Gibbs told me a few years ago that if I had a question about oil just look in the owner's manual. Unless you have a $50,000 race engine the manual is the best source of information. That sort of makes it easy."

If Porsche was updating the owners' manuals today they would list the oil as their synthetic 10W60 Classic Oil.

And the poster with the oil temp gauge pic of 250*, your oil pressure looks fine at over the 1 mark for ~850 rpm. Maybe the temp gauge is reading a bit high?

[rnln]

Thanks Frank for doing the reading for me before I even get to it.
Thanks everyone.

[winders]

Originally Posted by RichardNew

The correct answer here is "It Depends"

The issue here is Shear Stability. Shear stability is a measure of the amount of viscosity an oil may lose during operation.

Are you running a synthetic or an old fashioned oil?

Mobil 1 synthetic is supposed to be capable of protecting engines “at well over 400 degrees F”. Most race cars have no problem running synthetics up to 290 degrees F But - they get nervous when a conventional oil exceeds 270 degrees F.

A NASCAR Sprint Cup engine runs about 220F but the World of Outlaws run as high as 300F.

Joe Gibbs Racing likes to point out that the cooler your oil is the lower the viscosity you can use. Drag racers are using 0w-5. NASCAR uses 10W-30 and WoO use 15W-50.

Now - back to the basics. The folks are Joe Gibbs told me a few years ago that if I had a question about oil just look in the owner's manual. Unless you have a $50,000 race engine the manual is the best source of information. That sort of makes it easy.

Shear stability is not the only issue here. You are providing potentially dangerous guidance here.

Air-cooled engines can appear to be running within reasonable limits but the heads could be way too hot. In other words, the oil used could be operating in an appropriate temperature range yet the cylinders heads could be too hot.

The oil viscosity you use is based on operating temperature AND bearing clearances. That's why you check with the engine builder.

[winders]

250 degrees F is too hot......I don't care what oil you have in the engine.

[Franks89-911]

Winders, you said "Air-cooled engines can appear to be running within reasonable limits but the heads could be way too hot. In other words, the oil used could be operating in an appropriate temperature range yet the cylinders heads could be too hot."

I thought the oil temp gauge is actually connected to the cylinder head temp sensor? So it's actually measuring cylinder head temps, not the oil temp? Let me know if I'm wrong. Also, is there a way to verify whether what we're seeing on the temp gauge is indeed accurate? I've got an IR temp gauge, for example, where should I point it when my engine is hot to get the best reading for how hot the heads are?

Thanks for the advice.
Frank

[Franks89-911]

Allow me to answer my own first (noob) question.

Apparently oil temp and cylinder head are 2 separate sensors. And we don't have a gauge for the cylinder head temp sensor, just oil temp.




So, that begs the second question - since we apparently can't rely too much on the oil temp gauge to tell us how hot our engines really are/if we're within a "safe" operating temp, how can we truly tell if our heads are getting too hot?

[Joe Bob]

When I replaced the VDO clock, I installed a head temp and volt meter. Westach a aircraft control manufacturer did it 15 years ago. It's been useful and no failures.

[dfhtrhjn]

250 degrees? I wouldn't drive that 911 until you have an external thermostat and oil cooler installed, that's too hot. You're oxidizing your oil at that temp, and creating micro welds.

If you want to see what's happening just put some fresh oil in a sauce pan and heat it to 250 for say 30 min, then imagine that oil trying to lubricate a $15,000 engine.

[Steve@Rennsport]

Originally Posted by winders

Shear stability is not the only issue here. You are providing potentially dangerous guidance here.

Air-cooled engines can appear to be running within reasonable limits but the heads could be way too hot. In other words, the oil used could be operating in an appropriate temperature range yet the cylinders heads could be too hot.

The oil viscosity you use is based on operating temperature AND bearing clearances. That's why you check with the engine builder.

True wisdom, right here.

I'd add that high operating temperature exponentially increase the propensity for oil leaks and even more so if Viton seals, O-rings & gaskets are not used.

Keep your oil temps below 210 deg F and your engine will last longer, perform better and reduce operating expenses.

[scarceller]

On hot days always run these motors at 3000RPMs or higher while driving. I monitor every sensor in my 3.2L with my custom monitoring and logging solution and the Cyl Head Temps skyrocket on days above 85F and driving at 2500RPMs, CHT climbs by 40C easily! Then if I downshift a gear and get revs above 3000RPMs the CHT comes down almost instantly, within a minute or 2 she's back to normal. But the oil temps lag terribly as it takes a bit of engine heat to elevate the oil temps and once those go up it's far more difficult to bring them back down.

The reason CHT goes up so quickly at low RPMs is two fold:
1 - The engine fan moves more air at 3000RPMs than it does at 2500RPMs. Spinning it up at >3000 really helps.
2 - But the other huge difference is heat soak into the motor, consider that the amount of energy (air/fuel) needed to move the car down a flat road at 60MPH is about the same no matter if your in 3rd, 4th or 5th gear. Meaning the amount of air being ingested and the amount of fuel added to that air is about exactly the same to propel the car down the road regardless of RPM speed. You need to really think about this for a bit to better understand why this is so important to heat soaked by the motor. Let's do a quick example: Let's say your at 60MPH in a gear that results in 2000RPMs vs a gear that results in 4000RPMs. The taller gear at 2000RPMs will have about double the engine load than the one at 4000RPMs. Meaning that since the engine turns slower in that taller gear but still takes in the same amount of fuel and air then the injection pulse width (per stroke) doubles! This means that one stroke (2 crank turns) has to process 2X the thermal load! If instead you turn the motor at 4000RPMs to achieve the same unit of work (move the car at 60MPH) then the injection pulse width is cut in half and each stroke only sees 1/2 the work load!

I monitor everything in my motor very carefully and I know that no matter what gear I pick (2,3 or 4) at say 50MPH the air flow into the motor is nearly identical! This is very important to understand in these air cooled motors.

Here's another observation: have you ever wondered why some 911 motors have valve guides totally worn at 40K miles vs other engine with little wear at 100 or 200K miles? I guarantee that the motor with pre-mature valve guide wear has been lugged terribly at 2500RPMs or less, just go drive with that owner and you'll see. Given what was just explained about thermal load you can easily see how super hot valves and guides along with low engine fan speed could cause premature wear.

Now for the stop and go traffic and oil temps issue, try always driving at or above 3000RPMs in hot climates and if you must stop and go on a very hot day do not let the motor just sit at 900RPM while idling, rev it a tad and try to get that engine fan speed up, rev it to 2000RPMs if need be, I bet those oil temps get somewhat better.

Bottom line: oil temps go up long after CHT and thermal load has gone unchecked. Trying to lower oil temps can also be done by first addressing the thermal load on the motor. It's really easy to reduce thermal load under normal driving conditions, just increase the revs! WOT operation is a different story but basic street driving habits can easily induce elevated oil temps.

[winders]

Originally Posted by scarceller

But the other huge difference is heat soak into the motor, consider that the amount of energy (air/fuel) needed to move the car down a flat road at 60MPH is about the same no matter if your in 3rd, 4th or 5th gear. Meaning the amount of air being ingested and the amount of fuel added to that air is about exactly the same to propel the car down the road regardless of RPM speed. You need to really think about this for a bit to better understand why this is so important to heat soaked by the motor. Let's do a quick example: Let's say your at 60MPH in a gear that results in 2000RPMs vs a gear that results in 4000RPMs. The taller gear at 2000RPMs will have about double the engine load than the one at 4000RPMs. Meaning that since the engine turns slower in that taller gear but still takes in the same amount of fuel and air then the injection pulse width (per stroke) doubles! This means that one stroke (2 crank turns) has to process 2X the thermal load! If instead you turn the motor at 4000RPMs to achieve the same unit of work (move the car at 60MPH) then the injection pulse width is cut in half and each stroke only sees 1/2 the work load.

This is simply not true.

[scarceller]

Originally Posted by winders

This is simply not true.

Scott,

What part is not true?
You do not agree that the amount of air ingested by the engine is within 5% for a given speed in any reasonable gear? I monitor air flow in g/min in real-time and at 60MPH flat road 3rd or 4th gear the airflow changes no more than 5%!
Please elaborate on what part you disagree with?

If you have never monitored air flow I suggest you try it, you don't need to believe me, just try it. If you run a MAF it's actually very easy to just monitor MAF signal voltage for 2 gears at 60MPH. I gather my data real-time with a custom data logger that monitors the MAF signal.

I also monitor IPW of the injectors and if you double the RPM speed for a given condition (move car at 60MPH) you will cut the IPW in half. It may vary slightly but not by more than 5%.

Here's another way to think about this, if you leave the IPW the same and you double the engine speed you just doubled the HP put out by the motor, do you agree? And overall, torque remains the same.

Or think of this: it takes a given amount of HP to propel the car down flat road at 60MPH, that does not change. If you double the engine speed the HP requirement remains unchanged but at double the engine speed the torque requirement is cut in half and torque is directly proportional to load! So doubling the RPM speed just cut engine load in half. HP is a function of time while torque is not.