20W-50 Flash Point

[VirginiaF1]

My question centers on oil vaporization rates / oil burn consumption..

With my 1988 Porsche 944 non-turbo 8valve, I run Valvoline VR1 20W-50; this conventional racing/Dino oil Flash Point is 478F (248C)...
( I assume that is at 14.5psi? )

With current Virginia temps at 100F, what is the cylinder wall temperatures at say an average of 4k rpm?

For those using oils with lower Flash Points, does that equate to a greater oil burn rate?

Lastly, does 100F summer ambient vs. 25F winter temps really make any difference in these high temp equations?
( ie: running 15W-40 with an even lower FP)

As always, Thanks!
mikey

 

[A_Harman]

Yes, the Flash Point measurement is taken at atmospheric pressure.

There is no simple, straight answer to what the cylinder wall temperature is. Stabilized at max power a naturally aspirated engine can easily have cylinder wall temperatures at top ring reversal of 450F. This will vary from engine to engine depending on piston and water jacket design. How are you running the engine? Is this average of 4000 rpm something that you are doing in road course track days?

Generally on BITOG we associate higher flash points with the possibility of lower oil consumption, but it is not a reliable indicator. The NOACK number is a better indicator of oil consumption, but fewer product data sheets have it, so we have to fall back on Flash Point.

Yes, higher summer temperatures do cause the fluids in your engine to run hotter if you are driving aggressively. The internal surfaces of your engine will also be hotter at increased ambient temperatures.

For an 8-valve NA 944, I don't think you need a 20w50, but I do not generally advocate a 15w40, which is a diesel engine grade, for gasoline engines. Or you could mix VR1 20w50 with VR1 10w30, and come up with something like a 15w40. I think the 10w30 has lower FP than 20w50, so the FP of the mixture could be lower. A synthetic 10w40 would be a good choice for an engine like yours if you are driving hard on a hot day. What does your owner's manual recommend for an oil?

 

[VirginiaF1]

Thanks for the input A..
Rennlist and Pelican submitted question as well but this site is the oil authority.

The 24 year old manual has 4 viscs listed with no real insights/recommendations.

 

[ARCOgraphite]

On a water cooled engine at about 70hp/L thats not raced hard, I'd run a non EC/ non-resource conserving syn 10w-30 oil in that engine - or a motorcycle 4T like m1 r 4t or similar. That engine has a finned Al or Mg sump pan, IIRC.
- As far as oil consumption goes, on an engine that not past its service life, oil use is more a factor of clean ring lands and pistons than spec like FP or NOACK. I had lowest consumption using current 20 grade.

 

[mechtech2]

It's not just the cyl wall temps, but the rings, pistons, and CC temps that directly act on the oil.
I can't understand why even the best oils don't vaporize off more or burn more.
Probably movement of the oil and cyl walls to cool it down.