Quote:
Originally Posted by Irace86.2.0
You mentioned it somewhat, but is it possible the 10w40 oil is also the problem?
I am running 5w30 for the simple reason that Subaru runs 5w30 in all their FI applications, and I am boosted, but I could imagine running 10w40 or 10w50 on the track. With that said, I think I would drive the car for 10-15 minutes at low speeds/rpms to get the oil to operating temperature, with the concern of starving the bearings running the high viscosity oil.
There seems to be a debate these days whether higher viscosity helps to protect the bearings with a thicker layer of oil, or if it is bad. The argument is that pressures will be higher, which is good, but if oil flow rate is slowed then oil temps can creep up; thinner oil will flow faster, so it will deliver cool oil faster. Total system oil temps may not raise because the oil cooling measures post cooling could be adequate, but locally to any one part of the engine there could be a spike. Thick oil could also cause back pressure, creating resistance against restricted flow, which could be why outlet pressure is static in your chart after increasing inlet pressure.
Also, you mentioned thinner oil having less problems with cavitation. Why is this the case? Intuitively, it seems like warmer oil and thinner oil would result in more bubbles.
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Dude this is a discussion that has existed for ages and will probably never be settled, you can read for hours arguments for both on BITOG from very reputable persons.
I think in the particular case of an inlet restricted oil pump, higher viscosity is worse because it will cause cavitation sooner with the same flow. High viscositư will have lower intlet pressure than low viscosity because it creates a bigger pressure drop with the same flow. Once the pump is cavitating heavily, the thicker oil film the high viscosity gives you (it's only advantage, actually), doesn't matter because the oil just doesn't get to the bearings. This also depends on the PRV on that particular engine, so it becomes a complicated discussion. One of my engine failures was using Motul 10W60 oil, I used it thinking of the same reasons you describe.