Valvoline Synpower 5W-40

I have used oils as low as 10W-30 (RedLine with HTHS of 3.9) at Texas World Speedway in 103dF Texas summer heat--once--with oil temps in the 280dF range--as an experiment--<bunch of unstated caveats>.

I have also used 5W-40 and 10W-40 oils at the same and other Texas tracks. Finally, I have used 15W-50 oils at the tracks. The 15W-50 oils made the car a little sluggish and run a little hotter--295dF (in similar ambients) than the xxW-40 oils--285dF versus the 10W-30--280dF. These tests were performed over a 2 month summer and were all run in about 100dF-103dF temperatures in an F355 on street tires (B S03s) {lapping within 2 seconds of the lap record for that HP level, that weight group, street tires.

In all cases, the oil was dumped after the event--as one has "consumed" the additive package of the oil by running it that hard and that hot for that long. {Side note: comming home from the track I always notice that the oil pressure is 5 PSI lower that before going, and after the oil change afterwards, the pressure went right back to where it used to be. Even the best oils shear down under track use. Also note: I have never been successful at causing this pressure drop in the oil even when performing seriously stupid backroad driving (which I no longer do)}.

In my opinion, for track use the important number to look for/at is the HTHS number. Shell Helix had an HTHS number of <about> 4.2 cP, so you are looking for an oil with such an HTHS number for track use. Ferrari puts the RedLine on the oil thermometer at 305dF, so an oil with an HTHS of 4.2 should be good for up to 305dF. In my opinion, one should stick with 285dF with an oil of that HTHS number as the point where the driver says to himself, "lets save the engine." That 20dF is just about equivalent to a change of 1 grade thicker oil (25dF is a whole grade).

For cars that don't see street duty or cars that will be in a position where the driver will not slow down when the oil temp gets above 285dF, 20W-50 is probably the right oil up to 305dF-310dF. However it is always best to find the HTHS numbers and use something pretty stout (like HTHS 4.6-5.2 cP) for these applications.

If you find oil temperatures in the 320 range (as rifledriver indicated), you need to start using a xxW-60 oil (in my opinion). {Although for the life of me I can't see how you could get an F355 to such temps--and I have tried, really hard in really hot ambient temps.}

Also note: The various Mobil ONE oils generally run towards the thin side (viscosity versus grade) while RedLine and AMSoil run towards the thick side.

 

Brian- Warm oil pressure in my car after a 20+ minute drive is ~30 psi.

Taz
Terry Phillips