RP Oil Pressure

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Aug 22, 2005
I put Royal Purple 10w-40 in my '70 Olds 442, which is mostly stock. The cold oil pressure was normal, but once the car warmed up, the oil pressure was lower than with the oil I normally use.

I drained out the RP, and put the normal dino oil I typically use back in. The warm oil pressure returned to normal.

My opinion is RP loses viscosity as it gets warm.
My opinion is RP loses viscosity as it gets warm.

Well, so does your dino ..or just about any fluid that I can think of (even water as one member educated me on). It's just that your dino ..and the RP aren't at the same visc at whatever temp you're reaching and calling "warm". Unless it's mislabled, it's a 40 weight @ 100C/212F. Your dino will be thicker at lower temps then a synth ..virtually any lower temp. They should both provide the same pressure (+/-) at 100C/212F
what did your pressure drop to and what is it normally? As long as it's around 10lbs/1000 rpm you're in good shape.
Is the increased flow with the easyer pumping RP giving you a lower pressure reading? I would be willing to accept a little more flow for a little less pressure. More flow through the same passage equals less pressure, most of the time. More flow might also mean more heat transfer from the heat source through your oil and back to the pan. In other words, don't worry, and if you want to run the RP, just do it.
Oil pressure is normal? What is normal? What PSI at what temp at what RPM???
What 'typical oil' are you using?
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