For what it’s worth... I’ll make this short as I can. October 2019 I lost the pressure in my stock pump. Replaced that pump with a Melling 10295. Upon picking up my car the replacement pump was determined to be faulty and was replaced under warranty. December 2019, it appears there was more damage than originally thought, so off for a rebuild. Cut to July and I have a running engine and a new Melling pump, 10296, except that oil pressure drops to 13lbs at idle when it gets operating temp. Melling says it’s my problem. So I install new pump and it does exactly the same. Again, Melling says “it must be something in the engine”. So the engine is shipped to builder for diagnostic tear down, only to find nothing wrong. Builder runs the pump on a dyno with a plan to compare to a known good pump. My pump fails in exactly the same way as it did in my running engine.

No word yet as to how Melling will respond.

 

Sorry for your trouble, but I'm in for the information when you get it.

 

It sounds like a pressure relief valve spring problem. Perhaps Melling received a shipment of bum springs. If the spring doesn't meet proper compression rates, as in being too soft, the valve will open with too little pressure, thereby bleeding off any excess pressure. Except if the relief valve is fully open at 25lbs, there's no excessive pressure as the engine "sees" it. But 25lbs would be excessive if the valve is fully open, and the spring is fully compressed at, say, 15lbs. Hope this makes sense. 4 things I would be 100% sure about are;
correct O-ring installation, correct O-ring size, oil pump relief valve spring tension, and relief valve moving freely in the relief valve bore. Even reputable companies get a batch of bad springs from time to time, whether they're valve springs, or oil pump relief springs. Melling, being a reputable company, would be no exception. I hope this helps.....

 

If I understand your question correctly, you state the OE pump quit, first, followed by 2 Melling pumps. The LS series engines are supposedly pretty tough engines, therefore, I'd be inclined to question why the first pump quit, and determine if whatever did, hasn't sabotaged the next two pumps. With 3 failed pumps, I'd be looking pretty deep into the engine.....

 

I've had multiple, knowledgeable people tell me that the failure the pressure relief on the stock pump is a known issue. Google search on LS1 OIL PRESSURE yields a ton of results. This video is exactly what happened to mine, failed at idle just after startup: oil pump failure

There wasn't a whole lot of forensic examination with the failure of the OEM pump. The first Melling pump that failed was actually working as expected in terms of pressure but there was a loud "knock" sound emanating from the pump. Melling covered under warranty without issue, and also paid for the shop time to make the replacement. We gambled on any further damage to internals of engine and lost, which lead to a rebuild. Because of this damage this second pump was not used on the rebuild.

The engine was then completely rebuilt prior to the install of the next pumps. At start up the pumps two and three performed in the same way. Cold start, at idle, 55+#'s of pressure. As engine temp increased, oil pressure decreased down to 13#'s. Pressure readings taken from top and bottom of engine and were within 1# on gauge. At Melling's insistence that the pumps could not be the issue, the engine was removed and rotating assembly disassembled. Bearings were taken apart and measured and were all with the builder's expected tolerance. Builder is a very reputable shop and given the fact the pump performed the same on the dyno as on the engine tells me that the issue is 100% with the pump. It was just unfortunate that the pumps weren't checked on dyno prior to engine being removed for examination as it would have save a lot of headache, and shop time.

hopefully this fills in some blanks...

 

Once again, if I were you I'd look hard at the relief valve bore, the valve itself, and spring tension. You had posted, I think, that you had a known to be good pump. Remove the relief valve spring, and check it against your "new" pumps relief spring/valve/valve bore. You seem to have it narrowed down to the pump. I know the gerotor "gears" are supposed to be installed only one way. I've never tried installing them "backwards" deliberately, and don't know if they'll fit if installed backwards deliberately. If you know with 100% certainty that it is something in the pump, you're going to have to inspect every dimension against a known to be good pump. Also, you mention it being "dyno tested". How exactly are you doing this dyno test? Just trying to help. Has anyone checked cam bearing dims?

 

Clearly it's not an oil pump problem. Have you tried changing your oil pressure sensor? And your o-ring is installed correctly? What oil are you running?

 

Good questions. Assuming the OP is running hydraulic lifters, and they're not clattering, he must have a reasonable amount of oil pressure/volume. It may not be a LOT, but there is some....

I'm certainly not taking a cheap shot at the OP, but seriously, three bad oil pumps, all in a row?

 

I believe the OP has stated the car gauge AND mechanical gauge read within 1lb of each other. OOOPS, sorry, I'm incorrect on this. Don't see where he said that. But if he'd do the gauge to car gauge comparison, it is something that would eliminate some more possibilities. I'll bet this ends up being something that was overlooked.....

 

Yes, I would agree with you that 3 bad pumps is VERY unusual. I asked the OP how the "dyno test" of the oil pump was performed, and whether a known good pump was checked against the "bad" pump(s). I lost an LS motor once, because the rear most cam bearing walked towards the front of the motor, and partially exposed the rear cam bearing's oil orifice. So I also asked him if the rebuilds had new cam bearings installed, and if so, has their alignment with the blocks oil orifices been checked. The LS motors aren't priority main like the original SBC. If you have a real bad lifter bore, or a cam bearing wasn't installed correctly, or has moved, your oil pressure will suffer. OP, does your motor have piston squirters?

 

No doubt - agree 100%. What makes me think this is the same symptoms were exhibited with multiple new oil pumps, a stock bottom end, and a rebuilt bottom end (I would hope the builder put new cam bearings in.....but I guess shortcuts are taken daily in this game). Replicating identical oil pressures on a broken in motor and a fresh rebuild is essentially impossible, but definitely improbable. Either it's something very dumb like a sensor, or the OP has the absolute worst luck on the planet and needs to play the lottery.

OP, do yourself a favor and have a oil pressure sensor relocation kit installed, and put a mechanical gauge on it to see what the pressure truly is.

 

Totally agree. One other thing to check. I'm assuming OP has the motor out on a stand, or bench. If so, remove the rear engine cover, and check if the "barbell restrictor" is in place. It's a small piece of plastic, at the bottom of the block, behind the oil filter, and looks like, well, a mini barbell, like a mouse would use!!! It's a round, white plastic piece, with an O-ring at each end. If it's MIA, or has damaged O-rings, OP will have no, or low, oil pressure. Since the pressure is fine cold, I doubt it's missing, but it may be damaged........

 

Nope, you're correct. Mechanical and car gauge within 1lb.

I do appreciate the assistance, but I don't have the engine as it's at the shop that built.

To answer a couple of the questions:
it's not three pumps in a row, it's 3 out of 4, not that that's anymore likely. The original failed pump was a 10295 which was replaced with another 10295, and it was working fine for two months until the residual damage from the first loss of pressure made itself known. Builder wanted the high volume pump so a 10296 was installed with the rebuild. Two of those then failed in the same fashion.

All bearings are new with the rebuild and checked measurements are as expected. The barbell is in place. Given that the shop's pump performs without issue tells me that neither of these possible culprits are at issue.

The pump dyno testing was done at the engine builder's shop. It was their "good" pump that was compared to my failed pump. Their dyno uses a separate device to run the pump; the oil pump is not bolted to the block, which takes the oil pickup and O-rings out of the equation. The block is heated with circulating hot water to get the block to operating temp. The pump is driven to push oil through the engine where pressures are measured at the filter (crank pressure) and at the top of the block (cam bearing pressure). Their good pump maintained pressure throughout the engine temp range. The block is then cooled and test started over again with my oil pump. My pump performed the same on the dyno as it did when installed in the car; 55lbs with cold block and 13lbs with the block at operating temp.

I don't know if they've inspected the pump bore or spring pressure, not sure it matters at this point.

 

Actual numbers are always nice to have for bearing clearances.

 

What brand is their good pump?
Also, GM makes a perf pump. I got them from Brian Tooley Racing.

Sure would like to see a photo of this test rig being used.

Ron

 

I don’t recall the bearing numbers.

The shop’s good pump is also a Melling high volume.

Sorry, no pics of the pump dyno

 

Buy the shops dyno pump!! Sorry, a little attempt at humor to lighten the mood. Anyway, early on in the LS history, GM had some bad pumps, where the relief valves were sticking open. Resolved long ago. As Ron said, go with the new GM pump. I hate to advise against a Melling, as they have a great track record, and I've used them many times, never once a problem. It sounds like the engine had checked out OK,, and gone over with a fine tooth comb. I suggested awhile back to check EVERY PUMP DIMENSION. Has the pump been checked as thoroughly the engine? You may be at the forefront of a bad pump production run. Nobody has that answer yet, but if your motor has fine oil pressure with the shops Melling unit, what else could it be besides bad pumps? Take a video of your motor with the shops pump, then change nothing except the pump, take another video of that, and send them both to Melling, as a "before and after" situation. I would think Melling would be most interested in these videos!! Years ago, I made up something myself to spin the LS pump with a drill motor. The oil pump drive hub was put on an ID grinder, and I ground around .002"-.003" out of it, until it spun freely on the crankshaft. Oiled up the crank and ID of the altered hub, and then spun it with a drill motor. Great priming tool......

 

So I have to ask at this point - how much have you spent in the removal and replacement of the engine, rebuild, and dyno time? I would imagine it would have surpassed the cost of a nasty LS3 swap or a new crate motor.

 

$$$$ the money question is the biggest of all. I was hoping it was something with the shop’s build so that it would have all been on their dime. Given that really does seem to be the oil pump I’m waiting to hear if Melling will step up...

 

Good luck and keep us updated. It will be tough to swallow if a $150 part ends up costing thousands. The builder should have done a few other things before tearing the motor down as well, so hopefully between the two it works out in your favor.