Any oil pressure experts out there?

rav3 · March 11, 2023

Can anyone explain to me how the oil pressure is regulated on my '17 Silverado 5.3 V8? Under normal running RPMs, the oil pressure guage shows approx. 40 psi. However, when I'm going downhill with my brakes on, the Hill Decent braking comes on & it shifts the transmission down to help slow the truck down. Once the engine hits about 3500 RPMs, the oil pressure jumps to approx 60 PSI. I'm curious how this is done. I assume that there's an electronic valve that turns off the pressure bypass valve. But that would mean that the oil pump is producing the 60 PSI all the time, with a relief valve reducing it.

Can anyone explain what is actually going on inside the engine for this.

CamGTP · March 11, 2023

This article explains on the variable oil pump works.

https://www.underhoodservice.com/variable-displacement-future-oil-pump/

The pressure is controlled through the computers calibration, when a certain threshold for met the pump will increase the oil pressure.

rav3 · March 11, 2023

Very interesting info. Can I assume then that our 5.3 L engine has a electrical controlled variable pressure oil pump?

Grumpy Bear · March 11, 2023

9 minutes ago, rav3 said:

Very interesting info. Can I assume then that our 5.3 L engine has a electrical controlled variable pressure oil pump?

Nope. Variable volume that results in variable pressure. Your numbers look normal.

Grumpy Bear · March 11, 2023

I'm looking for the exact numbers but your fine. If I find them in my thread I'll post them here.

rav3 · March 11, 2023

1 minute ago, Grumpy Bear said:

Nope. Variable volume that results in variable pressure. Your numbers look normal.

Thanks to both of you. This allows me to understand why the pressure changes.

Next question. Why? Why does the engine need a 50% increase in oil pressure above 3500 RPMs

CamGTP · March 11, 2023

Yes, our truck pumps are controlled electronically and mechanically. When the electronic side of the fails you get a check engine light and the pump will basically be at full pressure all the time.

https://www.rockauto.com/en/moreinfo.php?pk=12983501&cc=3315175&pt=5564&jsn=603

The increase is pressure should be thought of like a safety measure. The computer doesn't know what you are doing or exactly where you are driving. It's just seeing different variables and changing the pressure based on whatever parameters on set in the computer. Above a certain RPM having more oil flow is good because that will keep bearings cool, keep the pistons cool and push more oil through the oil cooler to keep things in check.

Grumpy Bear · March 11, 2023

Hot oil pressure minimums.

22 psi @ 1,000 rpm

30 psi @ 2,000 rpm

33 psi @ 3,000 rpm

LV1, LV3, L83, L86 and L96.

This information is on page 35 of my build thread, second post. These are test block pressures between the block and filter. On my truck the test gauge at this position reads higher than the dash gauge. By the dash I'm 30 ish idle. 40 to 3K rpm and 60 over 3K but on the test block it like 85 at 3K.

Edited March 11, 2023 by Grumpy Bear

Grumpy Bear · March 11, 2023

14 minutes ago, rav3 said:

Thanks to both of you. This allows me to understand why the pressure changes.

Next question. Why? Why does the engine need a 50% increase in oil pressure above 3500 RPMs

Rule of thumb has been 10 psi per 1K rpm MINIMUM.

JimCost2014 · March 11, 2023

Why does the engine need a 50% increase in oil pressure above 3500 RPMs

In Laymans terms, It is spinning really fast and needs all the lubrication it can produce so it does not blow up.

rav3 · March 11, 2023

@JimCost & Grumpy....Thanks for the education on these newer oil pumps. I was not aware of this sophistication & how it has changed over the years. It all makes sense now, for this Old (retired) Jarhead. You guys have educated me well. Another little item in the mental library.

Now, armed with your information, I found this video that really explains how it works.

Edited March 11, 2023 by rav3

Grumpy Bear · March 11, 2023

8 hours ago, JimCost2014 said:

Why does the engine need a 50% increase in oil pressure above 3500 RPMs

In Laymans terms, It is spinning really fast and needs all the lubrication it can produce so it does not blow up.

Think of it this way. They didn't add more oil flow at high rpm. They took flow away at low rpm.

Faster a motor spins the more heat it generates the higher the flow to keep it cool. In addition, spinning crank at the rod journal is a centrifugal pump. Trying to pump oil out of the rod journal so supply needs to be higher to keep enough volume the journal doesn't run dry. Bearing clearances help control this as well. Even the placement of the journal oil feed hole has an impact.

There was a good engineering explanation in layman's terms on that last point in a Peterson's Publications paperback in the 70's called "How to Hot Rod the Small Block Chevy".

Low rpm motors don't even need a pump. Your Briggs & Stratton lawnmower is a good example. Once upon a time cars didn't have pumps either. Not pressure pumps anyway. Stove-bolt Chey 6 is a 'dipper'. Early Ford 4 bangers used splash to fill a channel above the cam and then it dripped to the cam. Harley and others used a hand pump to oil valve gear. A few pumps every few minutes.

Lubrication is fun, eh?