- Jun 1, 2020
- Los Angeles
Hi guys, I've been using Liquimoly 10w60 in my E46 M3 for years, and I have noticed that during hard track use, the average high RPM oil pressure drops off pretty linearly until about 260F at which point it starts to drop off more suddenly. You can see this in the X-Y plot of oil pressure vs oil temp below. Because of this I usually call it quits at this temperature to be safe. Pressure recovers after a cool-down and shows little to no change in measured pressure over the life of the oil. Blackstone reports have always come back great and I haven't had any issues, but it would be nice to be able to run a bit longer without having to cool down. These S54 engines already don't make a ton of oil pressure, and are obviously notorious for oiling issues so it always has me a bit worried. I've already done what I can within reason to try and improve oil cooling. It seems to dump a bunch of heat into the oil, climbing from 80-130C in about 3 hot laps. It is a "built" engine built to slightly looser tolerances than factory, so that probably isn't helping. Typically see 55-60psi at high RPM, dropping to 40-50psi by 130C (revving to 8000+ RPM). At this temp, I'll also see as low as 9psi at idle (950 RPM). I decided to go with a higher-flow VAC oil pump to help. The pressure is now in the 70-75psi range. My question is, is it possible the sharp drop-off in pressure at that particular temp a result of the type/brand I'm using? It has been very repeatable over multiple events and oil changes. I was considering trying a different oil brand & viscosity, possibly Motul Sport 5w50 or something similar, since now I can afford a reduction in peak oil pressure. Figured I could also gain a bit of cold oil lubrication over the current 10w60 (even though it doesn't get below 50*F here). I haven't been able to find much info on non-linear change in viscosity at extreme oil temps (HTHS?) and that maybe a higher-end ester-based oil is more stable at such temperatures? I change oil after a few track events anyway so I'm more interested in high oil temp stability and reduction in friction/temps, rather than overall life.