oil pressure questions.

I posted several days back about my cheap oil pressure gauge reading low.  I installed my other gauge with the small plastic oil line straight to the block and verified that I was getting over 30 at speed and 10 at idle.  I ordered one of the US made gauges from Kaiser Willys and installed it today with the rubber line and the metal hard line setup.  This one is doing the same thing that the old one was doing.  It pulses at idle and bumps between 5-10 hot.  If you shut it off and crank it back up  it stays at 0 until you rev the engine and it will come up.  It shows right at 28-30 at speed once hot.  Ive had the oil pan off to replace the pan and there was almost no sludge in the engine and the pickup was clean.  Is there something else I can check or is this fairly normal for an unrebuilt engine.  Im running straight 30W oil right now, would swapping over to 15W40 oil help any?

Edited by Ryan_289 - 26 May 2016 at 2:30am

The cam oil jet has been replaced with the smaller jet. The pressure is higher when it's cold. Closer to 15-20 at idle. How would I check the pressure valve? The engine sounds good and feels like it's got good power. No smoke.

your oil pressure seems to act the same way mine does. starting it it will stay at 0 psi for a few seconds and then you rev it it will then seem to act as it should . shows around 35 cold drops to about 10 at warm idle. my engine is also believed to have never been rebuilt but i did install a new oil pump from napa last year to try and get my oil pressure higher than it had been before which it did seem to increase it.

Did you make sure the oil pick up tube is flush with the block where it bolts into the block? I guess they can leak just a little bit there where the gasket is if it isn't square.

Yeah, if your cold oil readings are that much better....that is likley bearing leakage flow. Bearing leakage should be laminar flow and laminar flow is more sensitive to temperature than flow through an orifice (like the cam lube jet or oil pump relief). Only other thing out could be is oil pump side clearance, which is also laminar. 15-40 diesel oil is a good oil for these engines anyway.

You're just getting it back on the road right?  If I were you, I guess I would enjoy it for a little bit and drive it easy.  Just don't lug it down and load it up at idle.  Hydrodynamic bearings like oil flow and speed, so if you are pulling a hill or something, it easier on them to downshift and rev than to lug.   I guess if the manual says 5 psi, that is likley enough to keep from spinning bearings and keep it in good rebuild-able shape.  Leave the rebuilding for a winter day.

When you buy a new pump tear it down and measure the distance the gears are below the surface of the oil pump housing and side clearance of gears to housing. There is a spec in the manuals and it MUST have that gap. If not the pump will lock up.