Oil temp vs oil pressure

[rawavr4]

Ok, logic tells me the hotter the oil, the thinner it gets. My aftermarket gauges show hot idle @750rpm, 25-26psi oil pressure, oil temp @ 194°. After some spirited runs on the highway, temps got up to 235°. When I came down to idle after that, my pressure was 38ish at 800rpm and as the temp dropped so did the pressure, right back to 26psi @750rpm. I'm using rotella t6 5-40 w/ purolator pure1 filter. Gauges are autometer p/h/w with a sandwich plate. Is this normal? Because it seems weird to me.

[anyonebutme]

yes and no. Wide range oils contain viscosity modifiers that thicken as temp increase, and HD diesel oil contain a heavy additive package. So when the oil is fresh and hasn't sheered down, it will act as you see.

[rawavr4]

I never knew that. I thought all oils thins with heat. You learn something new everyday.

[J-Groove]

I never knew that. I thought all oils thins with heat. You learn something new everyday.

That is why they are rated at say 10W 40. It is a SAE 10 weight when cold and a SAE 40 weight when warm.

-John

[rawavr4]

That i knew but this is the first time I've noticed it. I was running 15w-40 during the summer but the car was down for my gauge install throughout the fall so I just noticed it now after switching to the 5w-40. Thanks for the info.

[R/T93]

You finally got it hot enough for the modifier to "activate", yes. Mine isles at 1.6 BAR, on lapping days after a cool down lap and I park the fans are still going and the idle is 2.0 BAR.
Kinda neat, eh? My pressure doesn't change till the oil hits around 105 C. You have awesome oil pressure, btw

[rawavr4]

I guess I did. And mine changes around 220°. The oil pressure comes from a new oil pump, coated clevites and gzp doing the work. I haven't seen under 20psi since the work was done and my low pressure warning light is set 15psi.