Oil Pressure too low ?

1941 - 1945, MB, GPW Technical questions and discussions, regarding anything related to the WWII jeep.
arnob38
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Oil Pressure too low ?

Post by arnob38 » Sat May 12, 2018 5:50 am

Hello,

I am worried that the Oil Pressure on my 43 MB may be too low.

I did a full oil change, to make sure I have the right levels
My gauge is hydraulic

I have the following Mesures
Cold engine 110° pressure = 20
Warming Up 135° pressure = 04
Running 150°, driving in 3rg gear at 40mph, pressure = 40
Hot 155° Idle pressure = 02
Hot 180° Idle pressure = 01

What do you think ? Is this too low ?

Video of the pressure measure here : https://youtu.be/p2Y1wShUjDk

Rgds

Arnaud


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dpcd67
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Re: Oil Pressure too low ?

Post by dpcd67 » Sat May 12, 2018 7:19 am

What oil did you use? I have had old L134s that ran on 40 pounds but at idle, barely had any. I just attributed it to worn bearings and continued to drive them. Is it too low for a new or excellent condition engine? Yes.
Nice video.
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Re: Oil Pressure too low ?

Post by dinof » Sat May 12, 2018 8:12 am

First off, don't run that motor anymore until you can confirm that the gauge is correct! Check that against another gauge to make sure it is truly low.
Question: What's the history of the motor-was it just rebuilt? What was the pressure all along it's history?

Let us know.
Dino Falabrino
On the "G" since 1998.
1943 GPW 102310 DOD 3-3-43
1928 Model A Roadster Pickup
1930 Model A Tudor
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Re: Oil Pressure too low ?

Post by artificer » Sat May 12, 2018 11:39 am

Dino is correct....BUT always check the oil is not diluted with fuel first....the oil level should not have risen on the dipstick & it should not smell of petrol.
Next check the oil pressure against a known good [master] pressure gauge.
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

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Chuck Lutz
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Re: Oil Pressure too low ?

Post by Chuck Lutz » Sat May 12, 2018 1:49 pm

Definitely try another gauge....that looks to be a Stewart-Warner STYLE Oil Pressure gauge but since I can't see the Stewart Warner marking at the bottom of the face and there are two screws on the face I can identify it as a REPOP.

I would suggest to you that the gauge is questionable....but again, you do have the correct STEEL tubing from the gauge through the firewall to the rubber tube that connects to the block, right?

If the jeep was here, I would try another gauge from my collection, but if you do not have access to another one....then you will have to buy the cheapest oil pressure gauge you can find and find the adaptors to replace the one in the dash. Maybe just get an adaptor to fit it directly into the block after you remove the 90* elbow.

Repop:
Oil Gauge REPOP RFJP Two Screw.jpg
Oil Gauge REPOP RFJP Two Screw.jpg (62.97 KiB) Viewed 1631 times
Original Stewart Warner:
SW Oil Gauge Correct.jpg
SW Oil Gauge Correct.jpg (206.44 KiB) Viewed 1631 times
Chuck Lutz

GPW 17963 4/24/42 Chester, PA. USA 20113473 (USA est./Tom W.)
Bantam T3-C 1947

arnob38
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Re: Oil Pressure too low ?

Post by arnob38 » Sun May 13, 2018 12:20 am

Hello,

The gauge is definitely a reproduction.

I just cleared the lines between the engine and the gauge : everything looks OK.

What bothers me is that I tested the gauge by connecting the Air compressor into it, and the gauge seems to be fairly accurate : same pressure on the compressor gauge and on the jeep gauge.

I am getting worried that this may not be a gauge issue :(

Assuming this is a not a gauge issue, where shall i check first ?

Thanks for your very useful advise !

Arnaud

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Re: Oil Pressure too low ?

Post by irakli » Sun May 13, 2018 2:44 am

Have you checked absence of the petrol in the oil as advised by artificer ? Do not ask how I know that :(
If yes, next step could be checking the engine compression.
Next - using 20w-50 oil, rebuilding pump...etc.
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Re: Oil Pressure too low ?

Post by dinof » Sun May 13, 2018 5:48 am

dinof wrote:
Sat May 12, 2018 8:12 am
First off, don't run that motor anymore until you can confirm that the gauge is correct! Check that against another gauge to make sure it is truly low.
Question: What's the history of the motor-was it just rebuilt? What was the pressure all along it's history?

Let us know.
2 questions I asked are still unanswered. It can be anything to a worn out motor to as simple as the orfice missing on the timing chain cover. Or this can be remedied with a new pump. You also need to own the TM's and read them. Oil pressure parameters are mentioned.
Dino Falabrino
On the "G" since 1998.
1943 GPW 102310 DOD 3-3-43
1928 Model A Roadster Pickup
1930 Model A Tudor
1968 Taco Minibike

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Re: Oil Pressure too low ?

Post by arnob38 » Sun May 13, 2018 6:48 am

Hello,

I just got my Jeep 6 months back, and apart from a first long 80 miles drive to get it back home when I purchased it, i have only been a couple of times around the neighborhood since then for short 15 minutes drives. I have my first Jeepers meeting in 2 weeks from now.

I just noticed that the oil pressure was low after a drive 2 weeks back.
Does not mean that the issue was not there before. Just that I may not have noticed it : I was just checking when engine was cold or while driving, and as pressure was looking OK, I did not bother too much.
But I was not checking at idle at the end of the drive. I just noticed it when during 1 drive, the oil pressure dropped to zero during 20 seconds before coming back to "normal"

The engine was fully rebuilt in 2016 be previous owner, and on the invoice there is one line showing "oil pump" , but what was exactly done, I don't know.

I am running with 20W50 oil, the Oil level is stable, and there is no smell of petrol at all.

I also have the TM manuals, both TM9-803 and TM10-1349, and I have been thru the sections regarding low Oil pressure
Image

There is more info in the TM10-1349 (in french), explaining how you can play with washers to adjust the pressure.

But in my case, as pressure was going close to 0, it doesn't seem that this is just a matter of adjustment.

Not sure where to go from her to be honest.

Rgds

Arnaud

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Re: Oil Pressure too low ?

Post by dpcd67 » Sun May 13, 2018 6:58 am

Put a new oil pump on it. Now that you said your engine is a fresh rebuild, assuming they did it correctly.
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Re: Oil Pressure too low ?

Post by Wolfman » Sun May 13, 2018 7:32 am

Adding shims to the oil pump pressure relief valve will not have any effect on low idle pressure. This sets the maximum oil pressure and should be checked with the engine warm.
Engine was rebuilt. ???? I have seen " rebuilt engines " over the years that described all kinds of things. Maybe a complete out of chassis rebuild to a fresh set of rings and bearings.
I like dpcd67's idea.
You have paper work showing what was done during the " rebuild". You don't know exactly what the "oil pump" was.
Maybe new old stock. Maybe a rebuild of a the old stock pump. ??? Don't know.
Your reading at hot idle are pretty bad.
I use Melling gear pumps. They are higher volume and hold better oil pressure.
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Re: Oil Pressure too low ?

Post by arnob38 » Sun May 13, 2018 8:33 am

Thanks Wolfman & dpcd67,

As you said, impossible to know what was exactly done....

I contacted Melling to see if they have Resellers in France or can ship to France.

Rgds

Arnaud

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Chuck Lutz
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Re: Oil Pressure too low ?

Post by Chuck Lutz » Sun May 13, 2018 9:55 am

One of the easiest ways to destroy/damage an oil gauge is to hook it up to an air compressor. The gauge is built around a Bourdon Tube and is not designed to accommodate ANY pressure above the 80 lbs +/- the face indicates. I still see no reason to attack the problem with wrenches just yet.

While I do consider you have worn bearings and they would still handle higher pressures generated by higher RPMS, I would want to cross off the gauge as the culprit for two reasons; first of all, it is a repop gauge ('nuff said right there) and second, it may have been damaged by "hooking it up to an air compressor"...just TRY another gauge to completely eliminate that as an issue FIRST.

However, if you read any of the posts about oil pumps, I think you will find that in the end, even a tired engine (worn crank/rod bearings) can generate decent pressure at high RPMs but at lower RPMS it can be an issue. In addition, those who have tired engines can usually get by with one lb. of pressure for every 100 RPMs...meaning at 600RPMs, you need only 6 lbs of oil pressure (that is if your gauge is not compromised!). So, IF the gauge is reading correctly at a hot idle, you have only one or two lbs of pressure and that is not enough.

x2 on Wolfman's post about shims in the pump. They control the maximum pressure, not the minimum.

Re artificer's post: I'm sure by now you have checked the level in the crankcase to see if gasoline has RAISED it and given it a "smell test" for raw gas so I guess we can assume you can cross that off the list.

So...where are we with this?
1) Worn out oil pump?
2) Wear on mains/rod bearings?
3) Faulty Gauge?

Using the "cheapest, easiest, fastest, simplest" criteria.....start with the gauge by trying another one. Secondly, borrow another oil pump and if that is the problem, buy another one(the Mellings are popular but some had problems at one point in time...) or get yours rebuilt. Note that the problem is rarely the pump though. Lastly, you need to get the history of what was done to this motor, when it was done, who did it and what that entailed (one man's "overhaul" isn't the same as a complete tear-down and going through!).
Chuck Lutz

GPW 17963 4/24/42 Chester, PA. USA 20113473 (USA est./Tom W.)
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Re: Oil Pressure too low ?

Post by dinof » Sun May 13, 2018 10:34 am

It's been recently rebuilt. Make sure the orfice is installed in the timing cover. Without it, can lead to oil pressure issues.
Dino Falabrino
On the "G" since 1998.
1943 GPW 102310 DOD 3-3-43
1928 Model A Roadster Pickup
1930 Model A Tudor
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Re: Oil Pressure too low ?

Post by artificer » Sun May 13, 2018 1:21 pm

Dino wrote:Make sure the orifice is installed in the timing cover.
What orifice. The only one I'm aware of in L134/F134 engines with a oil filter is the one in the oil filter stand pipe.
If the engine was rebuilt properly there should not be bearing problems with so little mileage/use. I suggest changing the oil & rechecking.
Mike correctly explained how the PRV pressure relief valve works & it has nothing to do with idle oil pressure unless stuck open. This is worth eliminating.
No-one in my memory has reported a Melling Jeep oil pump issue on the G.
There is nothing wrong with Melling oil pumps just some old furphy that keeps getting resurrected on here. https://www.google.com.au/search?rlz=1C ... 9voWpPF-Rk
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.


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