willysmjeeps.com

My M38 l134 runs around 40psi when I start and drops as the oil heats up - someone said you only need to worry about it if the pressure goes high. Mine drops to about 10 pounds. I do worry. Would a new oil pump keep the pressure a steady 30-40 which is where I'd think it should stay?

Pressure will always drop after the oil warms.

I found an answer - this is an excellent web page

http://www.gpwjeep.com/lubrication_system.html

Since the mains were done (I suppose, I bought it as rebuilt) when it was rebuilt and there is only a 2% chance the pump is the problem it is likely the cam - since I don't want to do the Ford cam brushing thing right now I wonder if thickening the oil might help?

That website lead me back here to this WillysM site with the same article - anyway where ever it originated it is a good explanation of the L134 lubrication system

It is a very good article on the lubrication system BUT the oil pressures quoted are very optimistic, even with the camshaft fully bearinged.

Would a new oil pump keep the pressure a steady

No, not necessarily. The pump provides FLOW, the pressure is created by restriction to that flow....so if your bearings are not brilliant your oil pressure won't be either. New pump or old it doesn't matter.

Best suggestion is to the change your oil before venturing off into the unknown.

You should expect about 10 psi @ idle hot & the adjustable PRV should be set up for about 45-50psi @ rpm.

20W50 Shell Rotella is a good summer choice 15W40 for winter.

Bill,
Help clarify what pressures you are seeing. 10 PSI at 45 MPH is not good. 10 PSI at idle is ok. At 45 MPH you want to see at least 35. Also give us the ambient temperature you are dealing with.

The causes for low oil pressure are, as mentioned, excessive bearing clearance on mains, rods, or cam. Also worn tappets and tappet bores. Finally worn oil pump parts can also result in low oil pressure readings. You didn't say what your temp gauge is reading. Also you should let us know if you are using the original 24 volt system and 24 Volt electric gauges.

Was there any plumbing changes to the oil filter system?
I read somewhere that there is a restrictor in one of the lines feeding the oil filter, and if it's not replaced with the same restriction in the hose it will cause low oil pressure (not good).

Bearbait

http://www.gpwjeep.com/lubrication_system.html
What you are talking of is shown in the oil filter stand pipe is in here.
Also in gear drive cam engines there is a squirter to the gears, where the orifice size was altered.

Yep Artificer you are correct, I remembered that there had to be a restriction for the bypass oil filter just couldn't remember where. As long as the original filter housing is used the restriction is not the issue.

Bearbait

You can use the Cuno, Military Junior or any of the Civvy CJ L134 filter like Fram and Puralator with no problem. On gear drive cam engines you can elect not to run a filter at all with no problem. On the early chain drive engines the return oil from the filter lubed the timing chain so running no filter reduced chain life.

The orifice in the spray nozzle for the gear drive cam engines was originally .070 but a few truly severe service engines were showing overheating of the #1 rod bearing so the factory reduced the orifice to .040 during production around 1950 and recommended the substitution of the .040 orifice in the field on severe service engines.