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Re: Oil viscosity

To: "Rob Dardano" <19to1tr6@mediaone.net>
Subject: Re: Oil viscosity
From: Randall <randallyoung@earthlink.net>
Date: Sun, 15 Jul 2001 12:31:47 -0700
jaboruch wrote:
> 
> It is strange to me that the pressure was back when
> things cooled down, unless the stuck regulator got unstuck as it
> cooled.

>From a hydraulic point of view, the oiling system is a fixed
displacement pump working into a more-or-less fixed size orifice (eg
bearing clearances), with a pressure relief valve.

So, while the pressure is below the relief point, more rpm = more
pressure.
And, because all motor oils get thinner as they get hotter (even 20W50
synthetic), more temperature = less pressure.

Joe's engine is tight enough (or his pump big enough) that his relief
valve is always open to some extent, hence his oil pressure stays fairly
constant at the relief pressure.

Rob's isn't, so he sees the pressure/rpm/temperature relationship I've
outlined.

IMO 25 psi at hot idle is plenty; 25 psi at hot 3000 rpm calls for
remedial action (new bearings) before the next race weekend; 25 psi at
6000 rpm says it's time to quit, right now !

It's also worth mentioning that original pressure gauges are notoriously
inaccurate ...

Randall

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