snives

I have replaced the pump. It didn't change the oil pressures. Hot idle I'm seeing 15.7 psi, 3500 rpm I see 20.9 psi. Taking the advice of 1redta I did an oil change and switched to a 5W-30 non-synthetic oil. It brought the psi up about 3 psi. Hot idle on 5W-30 I'm getting 18.6 psi, and 23.2 psi at 3500. I'm running out of ideas.

The vacuum pump taps into the main oil gallery, and returns it right into the pan. Does anyone know if the vacuum pump can fail in such a way that lets oil pass freely through it?

strutaeng

Have cam bearing been discussed?

snives

This is a fresh rebuild so it has brand new cam bearings. New cam, new rod bearings, new main bearings. Engine work done at a professional shop.

1redta

1redta

Just re read the bearing clearances nvmnd

isnt 10psi per thousand rpm the rule?

snives

Here's the oil pressure I'm seeing by rpm on the 5W30.

wretched73

iTrader: (1)

You built the engine or had someone else build it?

snives

I assembled the engine. Had a local engine machine shop polish the main and rod journals, hone the cylinders, install cam bearings and mill the heads, and 3 angle valve job.

snives

I am almost out of ideas, but it occurred to me that one thing that is not stock is the oil gallery barbell. I used one of those ImprovedRacing.com barbells with the seals on both ends. Their marketing states more oil flow, more filtration, but I'm beginning to suspect that is an outright lie. My theory is that the oil filter poses a flow restriction due to the filter media, and the higher the flow restriction the greater the pressure gradient you will see between the in and out. So this would manifest itself as a low pressure drop at low flows, and higher pressure drop at higher flows. When the bearings are cold and oil is most viscious that would be the lowest flow condition, and when hot with larger bearing clearances and thinner oil due to temperature the flow would be its greatest. Thus you would expect high oil pressure when cold, and low oil pressure when hot, exactly my symptoms! The oil filter itself has a pressure bypass at 15psi (different filters have different spring pressures), so the pressure differential can be at most 15psi. And with the oil gallery barbell effectively sealing off any bypass oil, the oil pressure to the engine would always be the pump pressure minus the filter pressure differential which could be up to 15psi. If I add 15psi to my numbers that would put me where I would expect to be.

The marketing of the oil gallery barbells says that the stock barbell "don't seal well and the clearance is poorly matched to the bore", but on the contrary, i'm thinking GM purposely did not put an o-ring on one end of the barbell, and purposely sized that barbell plug to be the precise size the allows the minimum amount of bypass oil to make up the pressure loss that any filter would impart to the system. As I type this I am convincing myself this is the source of my low oil pressure. I've ordered the stock part and waiting for that to arrive and we will see if that does the trick.

Anyone else have bad experiences with these double o-ring sealed barbells?

1FastBrick

iTrader: (17)

Or you some how damaged the O ring upon installation.
.