Low hot oil pressure

Tim52 · Post by **Tim52** » Mon Aug 29, 2022 3:28 pm

I presume this has been discussed at length, but I have been unable to narrow down the search for the correct forum, please point me in the right direction.

M38, L134 engine, ESN MC86303 About 10 hours on a professional shop rebuild. Low oil pressure when hot. 40-50 PSI on the gauge cold, engine sounds great. When at full operating temp (180 degrees) gauge drops to zero at an idle and the engine does not sound good. Several mechanics have listened to it, the consensus is that it is not rod bearing knock, maybe the fuel pump. At road speed, oil pressure comes up - 15-20PSI - but the rattle is still there - intermittently.

I am about to pull the front cover and install an oiler with the .040 jet, not knowing what the rebuilder used, in fond hopes of raising the oil pressure.

Any input / suggestions will be welcome. Including the location of previous threads on the subject.

Thanks

RonD2 · Post by **RonD2** » Mon Aug 29, 2022 5:32 pm

Hi Tim,
If it helps, here's a very good old post that describes the L134 oil system working. (It should be a "sticky" thread for easy reference.)
http://willysmjeeps.com/v2/modules.php? ... c&t=597%20

Just a few random thoughts:
What oil viscosity are you using?
Does it have enough ZDDP in it? (more isn't better)
Did you install a new or rebuilt oil pump? There's a relief spring and valve in the pump that affects oil pressure.
Maybe hook up a known-accurate oil pressure test gauge (not a replacement dash gauge) for a second opinion?

Yes, you should have the .040 oil squirter, and I could be mistaken, but don't think not having it will cause what you describe. No ZDDP and oil viscosity won't cause it either.

Do you have a mechanics stethoscope to help narrow down the source of the noise?

I'll search for other threads that might be useful....

Good luck!

Tim52 · Post by **Tim52** » Mon Aug 29, 2022 6:54 pm

Thank You ! That gives me another idea. I better double check the fittings at the oil filter. I had trouble with the line to the timing cover, had a great big, double wire hydraulic hose made. It got me home, but now I wonder if the fittings are right.

And yes, it would be smart to get a stethoscope. And yes - Do the diagnostics! Sometimes I need to be reminded. I'll hook up a mechanical gauge.

I've actually changed the oil twice already, the third time with straight 30W "racing" oil with zinc and used some Lucas zinc additive. The first oil changes were Carquest 10W30.

I believe the oil pump is new, but I couldn't find the bill so I'm not sure who's pump it is.

Thank You again.

RonD2 · Post by **RonD2** » Mon Aug 29, 2022 7:01 pm

Tim,
I forgot to say "welcome" on your first post. Welcome!

Here's another post dealing with cover gasket thickness on the oil pump affecting pressure:
http://willysmjeeps.com/v2/modules.php? ... ump+gasket

There's a small hole in the side of the center tube inside the oil filter canister that can also affect oil pressure.
It's supposed to be a certain diameter. Would have to research that measurement. Make sure nobody messed with it over the years.

If you search combinations of the words "oil pump pressure" I think you'll get lots of hits.

I'll let you do your own research on ZDDP (zinc) but I wouldn't add more ZDDP to oil that already has it.
The debate leans toward too much being a bad thing for these old motors.

Good luck!

Post by **wesk** » Mon Aug 29, 2022 7:49 pm

Looks like the rebuild was 10 hours ago by a professional shop. Since anything causing immediate low oil pressure should be considered Warranty Work I would slow down a moment and approach the shop that built the engine to stand behind it before you swap so many things they no longer are obligated to stand behind it.

Post by **Ryan_Miller** » Tue Aug 30, 2022 5:59 am

I think Ron and Wes have good suggestions.

On the large hydraulic oil line hose you had made - what is the diameter and length of that?

Tim52 · Post by **Tim52** » Tue Aug 30, 2022 7:01 am

Ron - Thank You, I should also have started my post with "long time follower, first time posting". I have found most of the information I needed without having to ask. I'll let you know how replacing the hose affects my problem. And I'll back off on the ZDDP.

Wes - Poor phrasing on my part. I am very slow about working on the Jeep, the rebuild was done 7 or 8 years ago, it only has about 10 hours of run time on it. The shop has changed owners recently so I'm sure I am on my own now. Unfortunately.....
I had pushed pretty hard to get the engine in and running way back when, and it sounded good then, but I never got it out and running down the road, never put any real miles on it until this year. One thing after another. It sat for quite a while, again. I am retired now and getting ansty to finish a project I've been working on for years.

Ryan - The hose is 1/4" 2 wire hydraulic hose made to order with crimped ends, etc. At the time, I was in the truck parts business and had access to what I thought was a better hose. It worked, didn't leak and is much beefier than what was there. However, hydraulic fittings are all about letting fluid flow, but if memory serves the original hose has quite a small orifice on the pipe thread end. I bought a correct hose at the time (now I have to find it), but never replaced it since the other one was "working".

Thanks again guys! Now I just have to find that hose. Worst case scenario, I'll rob it off my "spare" engine. I'll let you know how it works out.

Tim52 · Post by **Tim52** » Thu Sep 22, 2022 3:49 pm

Well gentlemen - No progress. I replaced the hose with the right thing and have now purchased a new Melling pump and installed that. Still virtually no oil pressure once the engine gets to 180 degrees.
I guess I need to dig deeper. I am suspicious that a plug got left out of the oil galley somewhere. Only one way to find out!

Thank you for the input.

RonD2 · Post by **RonD2** » Thu Sep 22, 2022 7:11 pm

Hi Tim,
Sorry to hear the problem still evades you.

I assume you're going to drop the oil pan first to look for the 2 internal gallery plugs before pulling the motor out of the jeep to take off the front and rear mounting plates to see if those 2 are present?

When you have the oil pan off, you might inspect your oil float for this: http://willysmjeeps.com/v2/modules.php? ... =oil+float

Including a good flat gasket seal on the mounting flange.

Good luck!

Post by **wesk** » Thu Sep 22, 2022 7:42 pm

It would also be a very good Idea with the pan off to check clearances on all Main & rod bearings with plasti-gauge and check crank end play. Another overlooked area is the lifter bores. Years ago you could buy .010/.020 OS lifters but today oversize lifter bores result in scrapped blocks. You should do all running pressure checks with known goo direct oil pressure gauge and it would be wise to alternate which cam journal pipe plugged port you use for the direct gauge. While we are talking cam after all these current check items are done and if no improvement in oil pressure then it's time to pull the cam and check the center and rear cam journal diameter.

That metallic clicking you are hearing could be just valve adjustment.

Post by **wesk** » Thu Sep 22, 2022 7:46 pm

Rond, Adding each common question related post to the board's sticky listing could very quickly fill up the entire first page and more. A better Idea is for a new volunteer to come forward and start building a Frequent Questions List and add that to our downloads page.

4x4M38 · Post by **4x4M38** » Fri Sep 23, 2022 6:01 am

I missed the part where you checked for the orifice fitting in the timing cover.

Tim52 · Post by **Tim52** » Wed May 28, 2025 4:47 pm

For anyone following my whole debacle with low oil pressure - "Here's your sign" Sure enough, even though the engine only had 300 miles on the rebuild, number one rod bearing is toast. Further disassembly revealed the problem. Although the engine and parts had been cleaned (hot tanked), they did not take the oil pick up screen apart. Bummer!! The only saving grace is that I didn't run it until the rod came thru the block!

Oh - and more evidence that I chose the wrong shop to do the work - all the ring gaps were lined up on top of each other - on all the pistons. Like someone thought that was the way to do it.

A second rebuild followed.... With a different shop! At least I didn't have to bore the cylinders again. Salvaged the crankshaft even. I managed to put about 3000 miles on it last summer, hoping to do even more this year. Super happy with the results this time around!!

Is it allowed to call out my engine rebuilder?

Thanks for all the input at the time!

RonD2 · Post by **RonD2** » Wed May 28, 2025 5:30 pm

Tim52 wrote:Is it allowed to call out my engine rebuilder?

Yes, especially if they did nothing to make it right.
How would anybody avoid the same pain you experienced if you don't name them?
If nothing else, give their address and folks can google it.

Glad to hear you got it fixed!

Tim52 · Post by **Tim52** » Wed May 28, 2025 6:06 pm

Regarding my engine guy - the first company is out of business, no point in bashing them - beating a dead horse and all that.

The second rebuild was done by Fergus Fleming Sr in Midland Michigan. He has several Jeeps of his own. The communication was great, he kept me informed throughout the process. Pictures, texts, etc. Fergus uses a machine shop in Midland that knows the Willys engines inside and out. The engine came back to me with a binder full of information. Results were better than expected. I have messed with both L and F Willys engines over the years; I have never had one run this quiet and smooth. I should have let someone who knew what they were doing work on them for me! As I said, I put 3000 miles on it last summer, it has run great.

Super happy with the results. Fergus can be found on Facebook.