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Re: Cold Oil Pressure

To: James Barrett <jamesbrt@mindspring.com>
Subject: Re: Cold Oil Pressure
From: Craig Wright <cwright@pdghightower.com>
Date: Sat, 05 Jan 2002 18:00:51 -0800
Hello James,

My guess is:

Your oil pump has an internal pressure relief that is set to probably around 
70-80
psi. They all do. So, it sounds like due to the higher volume pump, is 
exceeding the
pressure relief, maybe all of the time. This means that you have, say, 75 psi 
coming
out of the pump, hot or cold, because you are lifting the relief.  It is then 
pump
through the block to the filter adapter, through the lines to the remote filter 
and
then back to the filter adapter, where you are measuring the pressure. Due to 
the
head loss through the lines and filter, you will indicate something less than 
the
pressure out of the pump. When the oil is REALLY cold, like 30 degrees (I live 
in
California), the pressure out of the pump is the same, because the relief is 
still
lifting at 75 psi, but the head loss of pumping that thick cold oil is higher, 
in
you case 10 psi higher. I see this same issue in my 289 Shelby and 427 Cobra 
with
high volume pumps. It isn't a problem at all.

Craig WRight

James Barrett wrote:

> Folks,
>         Just had a cold wave hit Florida, got down to below 40 degrees.
> (For you Northern folks, remember that "cold" is a relative to what one
> is used to.)
>         I presently park my Tiger outside the garage under a car cover so
> The Tiger
> was cold at startup.  (Working on an Alpine in the Garage).
>         Now the wierd part: I normally have 65 psi indicated on my oil gauge
> when in normal running or idleing at 1000 RPM.  When I get in traffic for a
> long time, It may drop to 60 psi if water temp start to get above 90 degrees 
>C.
>         Today (in the cold) the oil pressure came up to 50 PSI and stayed
> that way
> until the motor warmed up to 80 to 85 C.  At warm up, the oil pressure 
>returned
> to 65 psi.  I was driving around 2000 to 2500 RPM in town. I use Valvoline
> 20W-50 oil due to the normally hot temperatures here in Florida.  I have a
> remote Oil Filter inside the fender under the driver's side headlight and
>  1/2" ID hoses connected to the original Tiger II fittings (both at the block
> and at the oil filter). I also have the original two tube Tiger II oil cooler
> in the circuit.
>
>         My previous experience has been that when the oil is cold, one has
> higher oil pressures than when the oil is hot.
>
>         I use a high volume TRW oil pump in my 351C.  The pump is less than
> a year
> old.  I also use a modified oil pan that holds 12 quarts of oil without
> hitting the
> oil hitting the crankshaft.
>
>         Any one have an idea of what is going on with the oil pressure
> during the "cold".
> Note that this "problem" is presently not serious enought to warrent pulling 
>the
> oil pan.  Would just like some ideas.
>
> James Barrett Tiger II 351C and others

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