Dea_944t

I´m installing a sender in the drain plug (I know you could argue that it should be installed in a sandwich plate at the filter instead)

What is the "recommended" max oil temp when measuring at the drain plug?
The car is more or less only used for track-days.

/Dea

quinnfiske

I used to run an early 911 in track events. Oil temp was and is a popular topic of conversation. Most people would try to keep oil temp below 250F. I would park my car when I got to 250 and never had a problem. Not sure about water cooled cars.

333pg333

Quite possibly depends on what oil you're using too?

Pretty hard to get a definitive answer on this. I've heard people say even 230f is creeping up a bit high. Depends also on how long you're out on the track, what sort of tyres you're using (as in grip levels), what methods you have to baffle sump. Best to dry sump ideally. How hot the oil gets influences the protection of course, that's why it's not just a simple temp figure to consider.

btw Dea, what springrates do you have on your Motons?

beentherebaby

250 F with a synthetic oil is well within the lubrication/durability range for the oil. Even dino oil will run fine @ 250 F. Many race engines run 280 F during a race without issue if the radiators get debris in them.

The hotter the engine temp the tougher it is on rubber seals and such even if the oil is fully capable of protecting the internal components. If it's track only then you're probably rebuilding the engine every xx hours so any reasonable oil temp. will likely work fine.

As a reference point some Euro car makers using synthetic oil start to throttle back engine power when oil temp exceeds 302 F. Not a typo, 302 F.

JDS968

Makes more sense when you convert it to 150 degrees C.

Anyway, pretty much any oil, even something really thick like 60 weight, is already VERY thin at that temperature, I don't think I'd want to run at sustained temperatures that high, like in an enduro.

Dea_944t

The track-day sessions are 15-20min, I run Toyo R888 or MPSC tyres and Motul 300V 15w50 oil (fully synthetic).

Main reason for doing the measurment is to see if I need an oil cooler.

333pg333: I have 120N/mm front and 160N/mm rear, pretty good compromise for a trackday car that sees some street use as well.

/Dea

beentherebaby

If your sustained oil temp is above 250 F then yes an oil cooler would be desirable for the reasons noted above. Many people prefer to keep the peak oil temps in the 220-240 F range but there is no absolute temp that is ideal.

333pg333

You can quite easily run a 993 oil cooler up to the standard 951 connections. I run up to about 115c / 240f max in a 15min session in pretty warm Australian climate.

Interestingly I have been reading a book written about the Ford gt40s and 917 era. They were running at endurance races with oil temps of 80c !

Chris White

That may be true as a ‘general’ statement but the 944 has its own set of rules!

The rod bearing failures are due to several issues that compound each other –
• An oil pump that can cavitate at higher rpm
• 90 degree corners in the oil passages in the crank shaft
• Oil level in the crank case that will hit the crankshaft under heavy braking and get whipped into a foam (at track)
• Very high oil temperatures (at track)
Put these all together and you get a hot, thin, foamy lubricant that will cavitate easily and not flow through 90 degree bends. Several of these items cannot be fixed but two of them can be carefully maintained – oil level and oil temperature. If you keep both of those in check you should not have a bearing failure. Let either one of them get excessive and you are gambling your engine.

So – the answer is really anything over 230 is not optimum. Anything over 250 not good. Anything over 280 and you might as well use stale beer as a lubricant!

JohnKoaWood

Better than drinking it!

Chris White

I save it for cologne…

fast951

Oil temps over 250F are not recommended. Ideally you want to stay in the 220-230F range.
When your oil temps go up, it could cause the oil pressure to drop. When the oil pressure drops, the temps will start to go up. Once you start the cycle, you are done, you need to bring it under control.

Running at higher RPMs can max out the oil cooling capacity, running a few RPM lower might solve it.. At least till you complete your track session.

You can never go too big on a oil cooler with a thermostat. Ducting and air flow is just as important (if not more important) than the size of the cooler.

I prefer to measure the temps in the pan as well after the oil cooler before the oil enters the engine.

Dea_944t

Thanks for the input!

So guidelines when measured at the oil drain plug is:

< 230F OK, no oil cooler improvement needed
230F - 250F Starting to get critical, monitoring of temp and pressure important
> 250F Oil cooler improvement needed

John: Where do you place a sensor to measure after the cooler? If I understand correctly putting a sandwich plate at the filter will mean measuring after the pump but before the cooler?

Chris: I always have the oil level at max, correct?

/Dea

Chris White

between half way and max on the factory marks - never over max!!!

Duke

My sump readings never exceed 90 C / 194 F at the track.