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I changed the rear main seal in my '52 M38A1 and then the motor sat around with little to no oil in it while I restored the rest of the rig. I just got the Jeep finished...on initial start up my oil pressure was zero(I have a 60 psi gauge). I read about priming the pump by dumping oil into the pump through the distributor. I tried that and the gauge jumped up to 30 psi but it never fluctuated with the rpms. I fine tuned the timing and carb over the last few days idling the jeep for probably 20 minutes total. Today I drove around the yard a bit and everything seemed fine so I took a 4 mile drive with the kids to get ice cream. I shut the jeep off we waited about 20 minutes then went to head home and the gauge read zero as soon as I started the engine....any thoughts? Weird that I would have pressure and then not. The gauge is working if I ground it it pegs. sender? Any help would be awesome.

First step with the military electric oil pressure gauge reading zero or low issue is to first confirm what if any oil pressure you really have. Install a permanent or temporary direct reading mechanical oil pressure gauge. When that's done post what it reads when you start the engine.

I once had a similar problem,had low oil pressure checked a dozen things ,decided to try a different oil wt .changed it from 30wt to 40wt oil and had good oil pressure for about 10 miles. After the engine had warmed up the oil pressure dropped(I know everyone is thinking"that's normal") but it dropped far enough that I thought I needed to look at some more things.
Turns out the fuel pump diaphragm was bad and letting fuel into my crankcase and thinning out the oil.
After fuel pump rebuild ,oil pressure stays put...40/50 psi cold..loses about 15/20 psi after good and warmed up.
Hope this helps
If it does turn out to be your problem debellas jeep has rebuild kits for original pumps for about $95 bucks

Is the oil pump new, re-built or ??? I had a similar problem with a supposedly "rebuilt" oil pump. The relieve valve spring was weak and would stick open. Ruined a brand new rebuilt motor. In retrospect, I will never use a "used" oil pump again. New is the only way to go.

Dan

CPEURO,

Try to stay organized in your troubleshooting. Focus on a proper list in the proper order. To grasp at each straw thrown up here results in "Shotgun Troubleshooting" which usually wastes your time and money.

Let us first know if the oil pressure gauge you have is telling you the truth. If it is not you have a simple instrument problem to fix. If the oil pressure is incorrect/low then start with the most probable and work towards the least probable. Go one step at a time and keep written notes on what you find in each step. You'll note that in your jeep's service manual TM 9-8014 page 82 Para 81 i. The first thing you check is oil level and grade then the accuracy and reliability of the gauge.

For example since you describe an intermittent low pressure issue and the gauge checks ok (Meaning the direct gauge shows low or intermittent low then first insure a steady oil supply to the pump. You will have to remove the oil pan and look for something floating around or stuck in the oil pickup screen. Inspect the screen closely for clogging. This means pull the cover off the screen. Make sure the screen and pickup tube are connected correctly and not allowing the pump to loos it's prime occasionally. Then move on to the pump itself.

I fixed it today....Thanks for the replies(I didn't see them until after)and thanks Pete Debella.....I went to the parts store this morning and got a mechanical gauge. The pressure was 40psi right off the bat(BIG sigh of relief). After talking with Pete Debella he told me to make sure the sender and gauges were grounded well. With a little sanding of the fresh paint the gauges worked great.

Do yourself a favor and add a ground strap from the instrument cluster panel to the main dash.

Thanks for the tip...I'll add the strap today