oil pressure??

[Shimy87]

Hey guys, heres whats on my brain now, want your guys opinion. Currently I run 10W30 and with hot car I have 35 lbs pressure at cruise and about 20 at idle. I think that is probably fine. Car has 71,000 miles. I have run 20W50 in the past and it really brings up the pressure at cruise and idle. Was overthinking this but due for a oil change and wondered if there is any downside to going with the 20W50 and the higher pressure? Was thinking with the higher miles and probably some larger tolerences from my beating on the car it might be a good idea. Also the 20 lbs at idle just bugs me even though I think thats fine?? What are your opinions? Thanks as always!

[TurboMonte]

You're just fine,,,20# @ idle fine,,,10# for each 1000rpm just fine also (cruise, etc.),,, 20W-50 also just fine (and it makes one feel better!).  Don't know what your climate is (or condition of car garaging/storage) so the higher viscosity doesn't give you potential starting issues.

Your build looks amazingly similar to my last/former GN.

[Steve Wood]

I run valvoline 20-50 in one of my cars because on really hot days out here, it drops down like that.  It is set up pretty lean.  I used to put 10-30 in it for cooler weather but then I used to change the oil pretty often too LOL

[Shimy87]

is there such a thing as too much oil pressure? I think I remember on a cold start with 20W50 it was 70ish LBS, warm cruise 45-50ish

[Steve Wood]

It's a bit complicated at first glance.  But, yes, it is possible to have too much oil pressure.

On the side of the oil pump is a big nut.  If you remove the nut, you will find a spring under it with a valve beneath the spring..  That spring determines the pressure at which pressure, the oil pump stops all the oil going thru the filter and, instead, starts bypassing some of the oil back to the pan so that some of the oil is not cleaned by the filter and flow is reduced to the oil passages.  This is to prevent the possibility of the filter media being collapsed which not only removes the cleaning of the oil but also prevents the oil from circulating thru the engine-near instant engine failure then results.

Basically, this bypass valve sets the maximum oil pressure the engine will see and many of us changed the spring to one that allows about 70 psi.  Seems like the spring was yellow in color.  Filter quality has a lot to do with the collapse point.  Fram were noted for media collapse whereas filters like Baldwin, Wix/Napa, Fram Racing filters were capable of handling more pressure.  Also, filter media plays a factor.  Filters that pass 40 micron particles thru the media don't collapse as easily as the "super" filters that catch stuff down to say 10 microns.

Basically, the spring under the big nut controls the high pressure limit.  If an engine has been run hard and not maintained properly, carbon/gunk can build up around the valve and prevent it from closing properly and we will see very low oil pressures in that case.  Modern oils help a lot to keep this from happening but it is still possible.

As the oil comes up to the operating pressure, the oil gets "thinner" and the pressure may not hit 70 psi after driving a few miles at idle or cruise.  If it is over 50 psi at wide open throttle on a hot day after driving some distance, it is fine on our cars.  More modern cars run much lighter weight cars and they don't need as much oil pressure due to much tighter clearances and better machining.  The old saw that states 10 psi of pressure for each 1000 rpm probably does not apply. 

AND, oil filters often have their own internal bypass filter so that they start bypassing oil on cold starts which again makes it beneficial to not run them hard until the oil is up to operating temp.

Our cars further complicate the issue by having a bypass valve in the oil cooler.  If you take the oil cooler out of the equation but leave the oil cooler adapter on the oil pump, DO NOT simply plug the cooler outlet and inlet holes with a plug.  This will force the oil cooler adapter to start bypassing oil and will greatly restrict the flow of oil to the engine which ain't good no matter where you live.  Simply take the adapter off.

If I had your problem and lived up there where it does not get super hot, I would try using three quarts of 10-30 and two quarts of 20-50 as Valvoline does not make a 10-40 in their higher zinc racing oils that I am aware of.

Oil pressure on the low end at idle is not very crucial as the engine is not really putting much load on the crank at idle.  Most cars immediately  kick the pressure up when the pedal is mashed a bit.

[Shimy87]

Thanks Steve!