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Old 02-15-2016, 08:50 AM
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My current engine starts out high - 60 PSI - and then quickly falls to 40 as it warms up.
My last engine started out at 20 and slowly built up to 40 over 20 minutes or so.

My only thought is restrictions of some kind or a bad pump = thick oil not being pumped very well. Lack of restrictions equals the usual cold oil is thicker which gives higher pressure.

Quote:
Originally Posted by hanleyclifford View Post
We have had other members report that oil pressure increases with time and temp increase after start up. I have tried to make sense of this because it is counter intuitive to my understanding and experience that viscosity decreases with temp and hence pressure should also decrease. One factor that keeps coming to mind is the nature of the oil pump intake. The "bottleneck" is the 1/8" NPT 90 degree street ell coming right off the oil pump. Since that fitting is a casting, it's cross sectional area is subject to the irregularities of the casting process. Even a small burr in the oil stream could have an influence on flow especially at cold temperatures. Because of the foregoing "theory" I have modified my oil pump to use a 1/4" NPT fitting. The difference in oil flow was impressive and could account for the big pressure differential I live with between start up and cruise. I live with it and enjoy the (relatively) massive flow and pressure increases as well.
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