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Replaced Oil Pump. Low pressure, no noise.

This is a discussion on Replaced Oil Pump. Low pressure, no noise. within the Internal Engine forums, part of the LSx Technical Help Section category; OK ... I am just crying right now. I'm still dealing with this low oil pressure issue. I've had the ...

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    Replaced Oil Pump. Low pressure, no noise.

    OK ... I am just crying right now. I'm still dealing with this low oil pressure issue. I've had the car parked over two years due to time I could allot to all the things I wanted to do with it while the engine was off the mounts.

    When I first crank it, it only registers about 38 PSI. As it gets hot, it drifts downward to about 10 PSI at idle. When I drove it before replacing the oil pump (I haven't driven it since I buttoned it back up this time, but I know what's going to happen), it has about 25 PSI oil pressure cruising. Oil pressure does vary with throttle. There are NO unusual noises. It idles just as good as before the low oil pressure. I took a chance once and throttled from stop on a deserted street. Performance seems as good as ever (I left a looooooonnnnnnnngggggggg set of black tire marks.) But, at idle, it is about 10 PSI. Scary. So I parked it for a long time.

    I finally had a mechanic friend of mine (this guy is good) take a look at the Rod Bearings with everything off the front, all the way back to the timing chain, and the oil pan completely off. (It took so long to get to this because since i would have the engine off the motor mounts, I saved up and bought Light-wieght K-member and A-Arms, QA1 Shocks all the way around, coil springs, panhard arms, ect., to get suspension back tight , reduce weight on front end and try to help my traction issues.)

    Anyway, back to my main story: he said the bearings have proper clearances. As a matter of fact, he said he rarely saw a bottom end in such great condition. He could even still see coating on the rods. Oil was clean with no shavings or debris. He said it looked as if the engine had never even been run. He said the builder defintely put good parts in it (Golden West Performance, if you remember those guys.)

    I had already hooked an external oil gauge up to verify the pressure does indeed follow what the oem guage is saying. So, naturally, we figured the problem was the oil pump. He went ahead and replaced oil pump, checking the that everything looked good. The concerning thing is he could not find anything wrong with the old pump, either. Which brings us back full circle.

    I dreaded the dissappointment I would feel upon putting it back together, but when I fired it up, sure enough ... same problem, even though the oil pump was replaced.

    My mechanic buddy suggests oil restrictors/galleys problems, maybe even oil plug issues? I don't know about those; he says it must be some kind of internal oil leak.

    We agree someone on the forum must have experienced something similar. I would appreciate any advice from you guys.

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    BTW ... not my first post here. I guess old members haved been purged from the forum database.

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    Member importhater81's Avatar
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    When you replaced the oil pump did you guys replace the pickup also?I changed oil pumps on lsx motors without taking the oil pan off and it is a bitch to get the pickup back on,point being it is real easy to bend or crack the pickup tube,or cut the oil pump to pickup o-ring.Another possibility is maybe the oil pump pikup screen is partially blocked.You said you had the pan off but sometimes even the best of them miss something.
    Last edited by importhater81; 01-22-2010 at 12:06 PM.

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    Quote Originally Posted by importhater81 View Post
    When you replaced the oil pump did you guys replace the pickup also?I changed oil pumps on lsx motors without taking the oil pan off and it is a bitch to get the pickup back on,point being it is real easy to bend or crack the pickup tube,or cut the oil pump to pickup o-ring.Another possibility is maybe the oil pump pikup screen is partially blocked.You said you had the pan off but sometimes even the best of them miss something.
    The pump was all the way off to check the rod bearings, so there was no crimping going on. Screen was clear. Only replaced what comes with the oil pump from the dealership.

    Indication is EXACTLY what it was before replacing hte pump, so I don't think anything changed, like cutting the o-ring or cracking the tube.

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    Member jb3golf's Avatar
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    Are you sure you double checked the Oil Pump O ring????? Sounds like its not seated right or pinched.......

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    The old timer rule of thumb for oil pressure was 10 psi for every 1,000 rpm. You indicated that it is 25 psi at cruise and varies with throttle. How high did it climb when you revved on it?

    I agree your pressure is too low. Absent a pickup restriction, an internal oil leak is the most likely problem. Someone on here should have some thoughts as to what it might be. What weight oil do you run?

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    Member importhater81's Avatar
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    Quote Originally Posted by Black LS1 T/A View Post
    The pump was all the way off to check the rod bearings, so there was no crimping going on. Screen was clear. Only replaced what comes with the oil pump from the dealership.

    Indication is EXACTLY what it was before replacing hte pump, so I don't think anything changed, like cutting the o-ring or cracking the tube.
    the o-ring doesn't come with the pump from the dealership...so if you didn't buy a new o-ring I'm assuming you reused old one??Not saying it is definately source of your problem but those o-rings are known to cause oil pressure issues.There is even a bulletin from G.M. about how improper installation from the factory or cuts in the o-ring will cause low oil pressure and possible engine noise.

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    Yeah baby! Yeah! silverWS6's Avatar
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    You went with the stock pump again?

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    Quote Originally Posted by jb3golf View Post
    Are you sure you double checked the Oil Pump O ring????? Sounds like its not seated right or pinched.......
    This mechanic is a pretty thorough guy. We worked on nuclear submarines together and he was a machinist mate on a ballistic missle submarine.

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    Quote Originally Posted by pajeff02 View Post
    The old timer rule of thumb for oil pressure was 10 psi for every 1,000 rpm. You indicated that it is 25 psi at cruise and varies with throttle. How high did it climb when you revved on it?

    I agree your pressure is too low. Absent a pickup restriction, an internal oil leak is the most likely problem. Someone on here should have some thoughts as to what it might be. What weight oil do you run?
    I didn't do a lot of revving ... just listening for noises and such. But, I recall it didn't go below that old rule. Just not what it was before. I run 5w30.

    When I went to the track, the oil pressure was always lower after a night of racing (I've been told the oil thins out because some fuel gets in it from racing hard ... others say racing just thins the oil out more quickly.) But I always changed the oil (usually the next day) after racing and the pressure would always come back to normal. This time it didn't.

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    Quote Originally Posted by silverWS.6 View Post
    You went with the stock pump again?
    Is your queston that I didn't replace with an aftermarket pump? Yes ... I bought a later year model new pump fron the dealership.
    Last edited by Black LS1 T/A; 01-23-2010 at 03:18 AM.

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    Quote Originally Posted by importhater81 View Post
    the o-ring doesn't come with the pump from the dealership...so if you didn't buy a new o-ring I'm assuming you reused old one??Not saying it is definately source of your problem but those o-rings are known to cause oil pressure issues.There is even a bulletin from G.M. about how improper installation from the factory or cuts in the o-ring will cause low oil pressure and possible engine noise.
    Just checked with him this morning.

    He said he is very familiar with the o-ring issue and took precautions to make sure it was properly seated. He looked at old one good upon removal and it was not distorted. He did replace the o-ring. Pickup tube was slick as a whistle. (his words).

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    Member jb3golf's Avatar
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    Wow bro this is a hard one to tackle here. Sounds like you did everything by the book......

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    Well shit,man sounds like you covered just about everything.How about the pickup to pan cleareance...i think the spec is 1/4" from pickup to the bottom of the oil pan,anyway this could have changed...i.e aftermarket oil pan?IDK just throwing out ideas.To the Op you said engine was rebuilt,did they change the cam or cam bearings possibly one of the cam bearings isn't aligned with oil gallery hole??That would sure cause a restriction up top to the oil sending unit boss but I would think you would have some kind of lifter noise if that was the case.

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    Quote Originally Posted by importhater81 View Post
    Well shit,man sounds like you covered just about everything.How about the pickup to pan cleareance...i think the spec is 1/4" from pickup to the bottom of the oil pan,anyway this could have changed...i.e aftermarket oil pan?IDK just throwing out ideas.To the Op you said engine was rebuilt,did they change the cam or cam bearings possibly one of the cam bearings isn't aligned with oil gallery hole??That would sure cause a restriction up top to the oil sending unit boss but I would think you would have some kind of lifter noise if that was the case.
    I drove it two or three years with the built engine in it. It ran stellar. It's a 422 Small block ... would rev 7K no sweat. Broke 4 trannies in that time. Had to go to a 12-Bot rearend cause I kept breking the 10-bolts. The engine was/is strong.

    No lifter noises.

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    I don't sell out! blackSS01's Avatar
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    Just taking a wild stab in the dark but maybe Cam bearings
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    it is the same thing I had and it was #2 cam brg walked out on me. now I am building a lsx. block. one other person had same problem rebuilt it even staked them and they still walked out again. he threw away the block that is what I am doing to. to much money to try it. good luck.

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    Member JRENIGAR's Avatar
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    My car has alot of highway miles on it and did the same thing when using 5w30. The book says 10w30 is acceptable from 0 to 100 degrees. I put in 10w30 and it has 45psi at idle now and Im driving it 110miles a day with 150k on it. Just try it, you never know???

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    Sounds like a bearing issue. And FYI, you can just "look" at an engine and tell if the clearances/tolerances are within spec.

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    Get an after-market guage.. If you're relying on the stock guage,,,,don't... If your motors' bottom end speced out fine the pump is most likely fine.. If it was failing, it would show on the engines internals.. There would be signs of it on the bearings surfaces and in the oil. Our cluster guages for the oil psi. and coolant temp guage are'nt always the most accurate. Just my oppy from having a couple issues like this with mine too.. Replaced sending unit still would'nt get above 65 ish psi on the guage. I grabbed a full sweep oil guage and did a test @ the sending unit sorce and found the oil psi to be correct @ the motor..
    Last edited by Smittro; 04-13-2010 at 04:16 AM.
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