# Low Oil Pressure-Bad Oil Pump



## PontiacJim (Dec 29, 2012)

My previous 400CI was freshly rebuilt. The day I fired it up, I watch the oil pressure gauge slowly climb to a little over 60PSI. Normally, oil pressure just shoots right up to 60PSI when you fire up your engine. Well, being newly rebuilt, I figured my "old" gauge was not working as it should, or there was some air in the plastic oil pressure line.

With valve covers off, oil was going to all rockers, so again, did not think too much about it. I replaced the gauge -no change. I swapped out the oil filter housing adapter on the block with another one -no change. I relocated the oil line from the filter to the oil hole next to the distributor -no change. Different brand filter -no change. Oil pressure was still very sluggish getting to 60PSI cold and once warmed, dropped to about 40PSI, but would climb slowly to 60PSI or better when I wound the engine up. I drove the car on a 2,500 trip with the oil pressure like this, and no changes.

I mentioned this to my engine builder. He said maybe the pickup on the oil pump had dropped off. Honestly never seen this happen, but who knows. I did confirm that the oil pickup tube was still in place (don't ask how I did this, 'cause I'll never admit what I did:wink2. Anyway, all looked well with the oil pump. The engine builder said I could pull the engine and he would figure out the problem, or just keep running it -it could go a day, or the life of the engine that way. Well, I wasn't going to pull the engine. This was my "toy" and I figured I would run it until it blew up, then I'd rebuild the engine again or replace it.

The oil pressure would go to 60PSI when cold, then drop to 40PSI driving when hot, and about 20 PSI at idle. Slowly these numbers got lower, so I added STP to thicken up the oil. Oil pressure would maintain, but eventually the thick oil was not working. Eventually the oil pressure would only hit 40PSI and at idle drop to under 10PSI. Then one day, no oil pressure on start up, and that was the end of it. I got 20,000 miles out of the engine over 7-8 years of driving -and I did not baby it.

Pulled the engine down to see what I could find. Bearings of course were wiped out and crank scored up. Pulled the Mellings oil pump off to inspect the gears/rotors. Nothing wrong here. Then I pulled the pressure relief valve -the check ball and spring. I looked down the passage to see something black inside. I managed to get it out, and the photo shows what I found.

Inside, and wedged between the check ball and housing were these 2 pieces of hardened rubber bits -pretty big stuff. I never had this pump apart, just bolted it on right out of the box. Screen in place, it could not have picked it up from the pan. It would have not come from the oil filter as the oil filter was past the oil pump in the system. Remember, this problem was there right from initial start up.

The rubber bits were in the housing so long, that it stained the check ball. The bits of hardened rubber were holding the pressure relief valve open, not allowing the oil pressure to build up as it was supposed to. My conclusion is that these small bits of rubber were in the pump from day one -it came from the factory this way. Maybe the small rubber bits came from a rubber belt used in the machining/finishing/or assembly process. There is no way they got in there from the engine assembly process, or through the oil system -and there is nothing that I could come up with that matched the hardened rubber bits.

So if you should ever experience such an oil pressure symptom, it could be a bad oil pump/bypass valve. I will check my next oil pump by pulling the oil pressure relief valve to ensure that it is not stuck and ensure that there is nothing in the passage to cause any problems like this again.:thumbsup:


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## geeteeohguy (Feb 2, 2008)

Another high quality replacement part! What a huge PITA. I would be seething.


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## BearGFR (Aug 25, 2008)

..no kidding. And you can bet that Melling would be hearing from me.

Bear


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## PontiacJim (Dec 29, 2012)

BearGFR said:


> ..no kidding. And you can bet that Melling would be hearing from me.
> 
> Bear


Yep, I even asked my new machinist about it. He at first said I sucked up a piece of valve stem seal off the pan and it bypassed the oil pickup screen. Then I told him the oil pressure was not right from the minute I fired it up to break in the cam, he thought it had happened sometime later. He said he had experienced where the check ball on an oil pump had not been correctly installed, I believe he said it was hung up on a burr. Kinda why I initially figured my oil pressure gauge was not working correctly with the new rebuild.

I can't prove much and I am sure its a one in a million of anything like this ever happening -just my luck, though. Now I know to simply give the pump a good once over for safety sake and peace of mind. How many people do you know of who have found a chunk of rubber in a can of corn and small sand like pebbles in another? (that got me a whole case of free vegetables via UPS from the manufacturer and an apology after I mailed them the chunk of rubber -and I was satisfied with that as things happen.) 

PS, buy the "No Salt" vegetables because all those foreign countries that we get our vegetables from hate us and that salty water in our vegetables is them peeing in the cans.:yesnod:


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## the65gto (Oct 9, 2008)

Being a little paranoid sometimes, whenever I put in a new oil pump/pickup, I put a gob of putty on the bottom of the pickup, install the oil pan (no bolts etc) and then remove it to check the clearance.


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## BearGFR (Aug 25, 2008)

the65gto said:


> Being a little paranoid sometimes, whenever I put in a new oil pump/pickup, I put a gob of putty on the bottom of the pickup, install the oil pan (no bolts etc) and then remove it to check the clearance.


That ain't paranoid, that's good engine building practice. :thumbsup:

Bear


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## rickm (Feb 8, 2012)

I have seen Pontiac valley pans after being put through the hot tank in a machine shop have tiny bits of hard rubber still inside from the old brittle dry rotted pcv grommet.


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## PontiacJim (Dec 29, 2012)

rickm said:


> I have seen Pontiac valley pans after being put through the hot tank in a machine shop have tiny bits of hard rubber still inside from the old brittle dry rotted pcv grommet.


I have no doubt. I am sure my pan was clean. I just chock it up to sh*t happens. I wasn't too upset over it as I know with any build things can and do go wrong. I didn't drive the car much as it was the "toy", so I go as much out of the engine over 7 years as I did on the new tires I smoked off until they were slicks, 20,000 miles. Was the perfect excuse for me to start rebuild #2 from the ground up and a bigger 455CI -and it too has had its share of problems and sh*t happenings......and it's far from over I am afraid.:yesnod:


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## PontiacJim (Dec 29, 2012)

OK, some more investigative research on the oil pump situation AND one more thing to look at that may have been the cause of it all - the PICK-UP SCREEN.

I decided to compare my new Mellings oil pump & pick-up with the Mellings oil pump & pick-up from my 400CI build that went bad. Got three photos for all to see. _Houston, we have a problem.
_
First, I bought a rebuild "kit" which included cast pistons and all needed gaskets at a reasonable price aimed at a stock type rebuild. I wasn't going big HP, just nice mild street with sporty cam for some get up and go. It was intended to be a driver when needed, yet be fun -and it was.

The kit had a Mellings M54D oil pump. The kit also came with the oil pick-up for the pump which I installed. Now here is the problem. My machinist mentioned that I could have sucked up pieces of valve seal. What? How does anything that size get past the screen? 

I began to think on this as I thought the purpose of the screen was to prevent the larger objects from getting into the oiling system. Wrong. *The screen does that to a point*, but if the screen should get clogged, there is a hole in the screen just under the crossbar which covers it under normal conditions and opens up by being sucked down IF the screen get clogged -you don't starve the engine for oil, but you won't know it either. Found this info on the internet in my researching.

Well, I had bad oil pressure from the immediate start up in breaking in the cam, as noted earlier. Learning about the operation and function of the screen on the pick-up, I decided to compare. *Holy Smokes, Look what I found!* 

Photo 1 is a side by side comparison of the old screen and the new screen I just got with the same Mellings M54D-S (S=screen) which came as a boxed set with the pick-up/screen & gasket. The mesh on the old screen on the left is so fine that the 10W-40 oil I used would have never passed through it, let alone when I added the STP to thicken it up near the end of the engine's life. In fact it is so fine that you almost can't see the pick-up tube inside. Now look at the pick-up on the right which came with the pump in the boxed set.

Photo 2 is a better shot of the old pick-up/screen -the crossbar has been pulled up and out to show you the oil screen hole under it which normally presses up against the bar to close it off. (and no, the screen is not clogged up, its that fine of a mesh) You can see in the upper right corner about 2 o'clock where the screen has a definite curvature where it was probably being sucked down. The whole screen was like this the entire perimeter. This would, in my opinion, tell me that the oil pump was straining to draw oil through the oil screen relief hole and collapsing it -which was like trying to suck oil through a straw.

Photo 3 is a good shot of the new pick-up/screen. Can you tell the difference? The screen has a much bigger & open mesh pattern, and you can clearly see right through it to the oil pick-up tube. 

So now, my corrected theory is this: The Mellings oil pump was not the fault. The fine mesh screen starved my engine for oil and thus it was always slow to develop max oil pressure quickly - took about 6-7 seconds, more when cold. The suction of the oil pump starving for oil, collapsed the screen, exposing the by-pass hole within the screen as its means to draw oil. At some point, there was a small piece of rubber something floating around in the engine which eventually got washed into the oil pan. At some point, that piece was sucked up through the screen by-pass hole, up through the oil pump rotors and forced into the oil pump by-pass check ball -which was probably during one of my many 5,800 RPM blasts through the gears.:thumbsup: The chunk of rubber was too big to be dislodged, so the oil by-pass check ball remained open at all times -which further aggravated the low oil pressure condition by not allowing the oil pump to build up oil pressure in the system as it should have when the by-pass check ball/valve is closed. So I had 2 unknown situations taking place at the same time, which ultimately took out my engine.

Now the engine kit came with the pick-up/screen and is probably an inexpensive knock-off made for the kit rather then the obvious Mellings supplied pick-up/screen. If the screen had worked as it was designed to, the oil would have passed through the screen with ease and my oil pressure would have been good from start up. It would have also, most likely, prevented the rubber pieces from getting sucked up into the oil pump and sticking in the by-pass valve. It also causes me to consider the oil weight used in the engine. I like and used 10W-40, but many recommend the 10W-30, and maybe this would be the best way to go, especially with a new build engine having tight tolerances after what I learned about pick-up screens and how they work.


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## BearGFR (Aug 25, 2008)

Interesting indeed. ("Interesting" means it sucks that this happened but - bad as it sounds - I'm sure glad it didn't happen to me.)

Has to make you wonder..... how did that knock-off screen get into the kit when it's not what Melling supplies, and what happened to the screen that should have been in there? Questions I'd be considering posing to the kit supplier.

Thanks for the education about the details of the oil pickup and screen. I hadn't realized they worked that way but now that I think about it, it does make perfect sense.

Bear


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## geeteeohguy (Feb 2, 2008)

What Bear said. And thanks for the info on this end, too. I NEVER knew about the pressure relief hole in those screens. Luckily, never needed to, I guess! And, I _love_ the new definition of "Interesting", too! LOL. Glad your sharp sleuthing got to the root of the problem, and that you shared it with all of the rest of us. You probably will end up saving one or more engines for other poor souls by doing that alone!!


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## PontiacJim (Dec 29, 2012)

BearGFR said:


> Interesting indeed. ("Interesting" means it sucks that this happened but - bad as it sounds - I'm sure glad it didn't happen to me.)
> 
> Has to make you wonder..... how did that knock-off screen get into the kit when it's not what Melling supplies, and what happened to the screen that should have been in there? Questions I'd be considering posing to the kit supplier.
> 
> ...


Who knew?:confused

I bought the "kit" probably 9 years or so now. It had those cast type pistons that Geeteeohguy said were not very good with what looked like 8 valve reliefs -double layered. So not much I can do at this point. I now know what to look for, though.:thumbsup:

I never realized how the pick-up/screen worked, nor the oil pump with its by-pass valve. I thought that the cross bar on the oil pick-up was simply a brace of some sort. Did a bunch of internet reading to figure it all out. Also did not realize that an oil filter has a by-pass valve in it. And then there is that oil pressure spring in the engine/oil filter adapter. So basically, the oil pump can pump way too much oil at very high pressures during those wide open blasts. If all of the assorted by-pass features were not in place, you'd blow up the filter and pressurize the engine to the point that it could cause damage. So not a lot of oil gets filtered in those wide-open blasts -for good reason. Can you picture those staked oil galley plugs popping loose?

We are always learning something about our cars, good or bad, that can hopefully be passed on or used by others to help them. I am no expert by any means and continue to learn -unfortunately, sometimes the hard way, which for me is par for the course!:wink2:


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## randy1966GTO (Feb 10, 2013)

A fabulous job of Forensic Mechanics and thanks for the education!


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