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Any particular reason why you are running 20-50 or 15-40? Seems unnecessarily thick to me(for average Canadian temps). I've got an unopened, unknown mileage 440 and I run 10-30 in it. Oil pressure is the exact same as with the 15-40 which I have tried but no longer bother with. I don't fill the filter either, nor do I prime it, and after an oil change it only takes maybe 2 seconds or so before the needle in my cheapie mechanical oil pressure gauge shoots up to 76psi - the normal cold oil pressure reading for it.

I would try a different gauge, throw on a cheapie mechanical gauge before next time, just incase it's somehow a gauge/sender issue. Either that or try a thinner oil.



Well I read from various service books that the original specs on these engines called for a 20w50 so when I first got into these I just went with what was stated... However I have been wondering of late why such a thick oil is needed hence the drop to Rotella 15w40.