Oil pump issues.

[horrocks]

I know oil pump problems have been aired many times, but I've done the search and can't find one that quite answers my specific issue.

I recently installed an NOS pump, as the pressure in the original was dropping out. However, I can't get the new one to give a good median oil pressure. If I remove the two little discs in the relief valve spring housing, the needle on the gauge hits the pin and stays there when there is any throttle at all and the engine is cold. If I leave the jeep running on tickover for 15 minutes it does settle back, but I'm still seeing 55 to 65lbs on the gauge, with tickover at about 40lbs. This is patently too high.

If I put a thin brass washer under the valve spring housing nut, things improve. At startup she shows 40-55lbs. However, as the motor heats up to operating temp at about 190 degrees, this drops right back, with tickover at 10lbs, and operating pressures about equivalent to mph but falling on the flat in top gear, so 20mph/20lbs, 30mph/30lbs, 40mph 35 to 40lbs. At 50mph it runs up to not much over 40lbs. This all seems a bit too low.

I know this doesn't quite make sense, because the oil pressure release valve should only dump off pressure at high engine running speeds/high oil pressure to protect the engine from excessive oil pressures at high revs, and it shouldn't have any effect on the pressure at low engine running speeds.

The motor is a newly rebuilt wartime MB unit, and has covered no more than about 200 miles. The oil pressure gauge is an original wartime unit.

[Wolfman]

My first thought, where did you get the replacement pump ??
What do you know about it ??
Possible someone changed the relief valve spring ??
Your initial readings look like what a Melling High Volume gear pump produces.
Do you have the correct pump mounting gasket in place and do all the holes in the gasket line up with the holes in the pump & block ??
Have you removed the Pressure Relief Valve to be sure it is not sticking ??
Have you tried another gauge for comparison ??

[horrocks]

Thanks for the quick response Wolfman.

The pump came from a respected UK restorer, one of a batch that I think he bought from India. I visually compared it with my original pump, and it is identical. I myself swapped over the springs, in case it would make a difference, but it didn't. The pump gasket is correct, and all the holes line up as they should. I haven't removed the pressure relief valve, I will have to work out how to do so - any tips would be welcome?

I do have another (repop) oil pressure gauge, but tested against a calibrated one by my engine rebuilder it was innaccurate, it is under-registering.

[051743GPW]

I kept my rebuilt original on a shelf and installed a Melling. Oil pressure is too important.

[dpcd67]

I never use old oil pumps any more; I always use Melling and they do give highish pressures.
If yours came from India, maybe it was made there. Not saying it ain't NOS....

[wc56daveyboy]

Does Ron sell the Melling brand of oil
Pump?

I too would like to buy a new pump but not sure where to find

[dpcd67]

Yes, Ron sells both chain and gear drive Melling oil pumps. He seems to be out of stock at the moment though. I would call them....

[W. Winget]

What weight oil are you using, it could be changing viscosity too much as it heats up and reduces your pressure.
V/R W. Winget

[wc56daveyboy]

Yes, Ron sells both chain and gear drive Melling oil pumps. He seems to be out of stock at the moment though. I would call them....

I see that. I found a part number for a Melling #M53-A

This is the correct part number for a chain drive L-134 engine, yes?

And is is considered high pressure/high volume
Or is it a standard pressure pump?

[dpcd67]

804769 is the part number from Ron's parts page.
Mellings are the best oil pumps and will produce 60 pounds of pressure easily.
Unless your bearings are toast.
I use only Rotella diesel oil, 15W40, speaking of oil. It has zinc in it.

[wc56daveyboy]

Thanks DPCD67

I use only Rotella diesel oil, 15W40, speaking of oil. It has zinc in it

I too use rotella diesel engine oil.

Not sure what’s in my current motor. In fact going to buy some engine oil today

So have you ever tried straight 30 vs the 15W-40?

If so have you noticed any oil pressure changes from one to the other?

As I understand it, 15W-40 is a multi grade, where as the purpose is it acts like a lighter weight oil (15W) at startup but is or becomes a 40 wt after warm up?

[051743GPW]

The part number from the melling site is not really clear, however I find anecdotal info that the chain drive pump is Melling M-53A. Melling has a help line, too. States before engine 44417.

I have a Melling on my rebuilt 1943 GPW engine. 30 weight oil. Runs 20 psi at idle and 40 going down the road.

Mark

[W. Winget]

I think the Lube Order calls for straight 30wt. There were no Multi-viscosity oils back then, but there are those that know better than the TM's.
Oil additives should be filtered out by the oil filter if it is working correctly, so they are just snake oil treatments.
Try straight 30wt and see what happens.
V/R W. Winget

[dpcd67]

Of course it calls for 30 weight above 32 degrees temperatures and 10 below that, and below 0, PS.
They didn't have good oil back then; we do now, so yes, in this case, I do know better than an 80 year old TM.
Our modern gas is totally different too, you use that don't you?
But it has no lead in it.
I use Rotella 15W40 in all my vehicles; it contains zinc, and it does work well in all temperatures and under all conditions..
Yes, I have used straight 30 weight oil; when it is cold, it turns to molasses.
Of course, everyone is free to do what they want, as always. Even if it is not the best COA.
Think about it.

[dpcd67]

05; that 44K engine serial number means CJ engine; NOT MB engine number. ALL MBs have chain drive and CJ2A do up to serial number 44, xxx whatever you have above.