Normal Oil Pressure

[JimVillers]

We just assembled an engine after a complete rebuild.� We primed the oil pump and are using 30W oil (single weight).� �The tub is off the chassis so we installed a universal oil gauge.  It has a new oil pump.

What is the "normal" oil pressure?� Our gauge is showing about 20 psi with the engine running above an idle and close to zero at idle.� I pulled the fitting for the oil gauge and it squirted with vigor and volume.� �

Should we be worried?� Pull the engine to investigate?� My only thoughts would be to look for an air leak around the oil pickup.

[garage gnome]

I would be concerned with zero at an idle. I run 20W-50 in mine and at idle, when warmed up, it is at 20psi, unless it it really hot out, it might drop to 10. As soon as a give it gas, it, it goes up to 40psi.

Rule of thumb is 10 psi for every 1000RPM.

[1955CJ-5]

I might first try a different oil pressure gauge...

[JimVillers]

We put the tub on the chassis this morning.  If I didn't do it this morning, it would be two weeks before my son and his trailer would be available again.

I will try a different gauge and some other items to check the pressure.  The engine seems to run too well to have anything seriously wrong. 

[athawk11]

I run similar to G-nome.  I can get to 50 psi before it�s warmed up, but it tends to hover around 15-20 at idle when hot.

I have read that that having around 6 psi at warm idle and 20 psi at 2000 rpm when warm is acceptable and within specs on these old flat heads.

On a older worn in engine, I would point you toward a clogged pick up, an oil gauge issue, a weak pressure spring in the oil pump, and to do a compression or leak down test.

On a fresh rebuild�with a known good gauge, I would suspect the new oil pump.  Reproductions are known to have occasional issues.

[CJPilot]

Is your oil filter set up correct?  I believe it plays a roll.

[BMIC]

Would a missing timing gear oil fitting produce those numbers on a fresh rebuild?

[JimVillers]

I have the little oil squirter installed to lubricate the timing gears. 

I am not sure of anything special about setting up the oil filter; 90 degree fitting to the hose to a 45 degree fitting to the outside of the canister.  The hose comes straight out the bottom to the fitting on the timing cover. 

The starter is now out to be converted from a 12V to 6V so I cannot test anything until Monday or Tuesday.

[Mark W.]

Did you mess with the orifice in the timing gear squirter? Originally they were .070" and later WILLYS changed them to .040" to help with oil starvation in one of the bearings. Easy to check with a numbered drill bit. If its still a .070 you can easily braze the hole up and redrill it.

But 20psi at above idle is well within acceptable numbers.

[JimVillers]

An update and some thoughts.

Second oil gauge reads the same, almost zero at idle and up to 20 psi when reved. 

We changed the oil pump from the new pump back to the old pump, no change in oil pressure.

My thoughts are that there must be a large internal oil leak.  The pump will pump a large quantity of oil and it has a pressure release valve to limit the maximum pressure.  I inspected a stripped block to get any ideas to the cause.  My guess is that the internal plug with the slotted head is missing. 

Has anyone heard of this plug missing and what the symptoms were?  Any other thoughts?

[garage gnome]

Have you tried a thicker oil?

[athawk11]

There are a couple plugs in the oil galley.  If not installed, you would have a hard time keeping the pressure up.  The re-builder might have pulled them to clean the block...then forgot to re-install them.

Credit for Photo belongs to Flat Fender Fever!!!

[CJPilot]

I don't see how you could get "20 psi with the engine running above an idle" if one of those plugs were not installed. But maybe?

Two pumps with the same results kind of rules out the pump.


The other side of the oil galley feeds the oil filter.  If I were going to trouble shoot this problem I'd first try blocking off the oil filter feed hose. Next I'd pull the timing cover and check the timing gear squirter.

[JimVillers]

The good and the bad ..... I blocked the oil filter line as suggested with the first oil pressure gauge and it read the same pressure as the dash gauge.  Zero at idle and 20-25 max when reved.

I pulled the pan to inspect the two internal plugs and they were both in place, a slotted plug in the galley and a square head plug in the pick-up. 

Is there a gasket under the pick-up flange?  I don't remember one and it does not look like it has a gasket.  A air leak here could cause a lack of volume.

I am hesitant to pull the front cover to check the front oil squirter which I specifically remember installing and adjusting.  The replacement front pulley is VERY tight and it will be destroyed trying to remove it.

My next step will be to force oil into the system through the oil filter hose to see if there is a big leak someplace.  I plan on adapting my pressure brake bleeder with engine oil.  It will make a mess but hopefully provide some understanding of where the oil is going.  I have never tried this but it sounded like a good idea.
   
After that, we'll measure the main bearing gap with plasti-gauge.  This is not rocket science, just a simple engine and there must be something that is not right somewhere.

[CJPilot]

Yes, I believe there is a gasket under the pick up.