Junkyard shortblock... junkyard turbo... LOW oil pressure after warmed up?

[posduramax]

I dont wanna make this post to long because I get off track to easy so Ill try and make it short and to the point.

Truck comes in smoking its azz off and obviously running like crap...
Had injectors tested and 2 were supposedly bad so the owner wanted to go ahead and replace them all.
Got them all in and still smoking and running horrible no change at all.

So we do a compression test and find #7 cylinder down on compression.
Piston had melted and destroyed the bore..

We found a good used short block (or thats what they said) and I got everything buttoned back up and rans good but still smoking like some little man was under the hood dumping oil in the intake!.. but it wasnt running bad so I was sure the turbo was shot and sure enough the thing had about 1/2" of play on the exhaust side pouring oil straight into the exhaust

So then I got a junkyard turbo (looked great and clean) and got everything back together and took a deep breath.... It starts right up and runs awsome once all the oil residue gets burnt out the exhaust with a couple of wot pulls to about 80mph...

BUT when I pull back in the shop the low oil pressure light comes on and is in the red it did not do this before the junkyard turbo was swapped on. I checked it with a manual guage and it reads right around 8-10psi at idle and fluctuates abuot 2psi even when the truck is remaining at the same idle rpm

Im lost on this and dont wanna tear this engine back out...
If anyone has any info for me that would be great!!!!

Could a turbo cause low oil pressure once the engine warms up ONLY?
If its cold when I crank it, its around 60psi at idle but once its at operating temp it drops back to about 10psi or so

The oil does not smell like fuel and is still as clear as when I put it in..

Ive got to be missing something, this is my first duramax and so far it hasnt been a good experience

[TakeEm]

Originally Posted by posduramax

I dont wanna make this post to long because I get off track to easy so Ill try and make it short and to the point.

Truck comes in smoking its azz off and obviously running like crap...
Had injectors tested and 2 were supposedly bad so the owner wanted to go ahead and replace them all.
Got them all in and still smoking and running horrible no change at all.

So we do a compression test and find #7 cylinder down on compression.
Piston had melted and destroyed the bore..

We found a good used short block (or thats what they said) and I got everything buttoned back up and rans good but still smoking like some little man was under the hood dumping oil in the intake!.. but it wasnt running bad so I was sure the turbo was shot and sure enough the thing had about 1/2" of play on the exhaust side pouring oil straight into the exhaust

So then I got a junkyard turbo (looked great and clean) and got everything back together and took a deep breath.... It starts right up and runs awsome once all the oil residue gets burnt out the exhaust with a couple of wot pulls to about 80mph...

BUT when I pull back in the shop the low oil pressure light comes on and is in the red it did not do this before the junkyard turbo was swapped on. I checked it with a manual guage and it reads right around 8-10psi at idle and fluctuates abuot 2psi even when the truck is remaining at the same idle rpm

Im lost on this and dont wanna tear this engine back out...
If anyone has any info for me that would be great!!!!

Could a turbo cause low oil pressure once the engine warms up ONLY?
If its cold when I crank it, its around 60psi at idle but once its at operating temp it drops back to about 10psi or so

The oil does not smell like fuel and is still as clear as when I put it in..

Ive got to be missing something, this is my first duramax and so far it hasnt been a good experience

The turbo couldn't cause low oil pressure period unless it was pouring out one of the seals. You would obviously see if there was an oil leaking issue.

You have something else going on.


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[TakeEm]

What engine is this?


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[posduramax]

Lb7

[posduramax]

Originally Posted by TakeEm

The turbo couldn't cause low oil pressure period unless it was pouring out one of the seals. You would obviously see if there was an oil leaking issue.

You have something else going on.

thats what I thought, the oil pressure was fine before the turbo swap but that doesnt mean something didnt go wrong when I test drove it after I got the newer turbo on. My boss just seems to be sure that something is wrong with the new turbo... lol

[boostnlb7]

why is it idling at 8-10 psi? and an oil pressure sending unit or sensor could not be reading right and causing it to say low oil psi..if its sending a bad reading then the computer thinks its got low oil psi.. im still curious to know why your boost is pressured at an idle.. where did u take the reading from?

[clinebarger]

I know this truck is pissing you off (Im a Mechanic also).....But you could have picked a better username

Your oil pressure is low. 14psi at hot idle is minimum. On a healthy Duramax I like to see 25psi.
What oil are you using?
Plugged oil filter?
Do a "paper towel test" on the oil. Fuel will migrate away from the oil.

Other possibilities.....
◦Malfunctioning oil bypass valve
◦Oil pump worn
◦Oil pump-to-engine block bolts loose
◦Oil pump O-ring damaged or missing
◦Oil pump to oil pump tube gasket missing or damaged
◦Oil pump tube restricted or cracked
◦Oil cooler restrictions
◦Oil cooler O-rings damaged or missing
◦Excessive bearing clearances
◦Cracked, porous or restricted oil galleys
◦Oil gallery plugs missing or incorrectly installed
◦Damaged or missing oil spray cooling nozzles

[posduramax]

I thought the username was appropriate at the time lol...

Mobile Delvac 15w40 I believe

I already changed the filter (again) and it didnt help

I will try the paper towel test tomarow

I know there is no way to drop the pan without pulling the engine, but can you possibly get to the oil pump with the engine still in the truck? Probly a stupid question....

Would any of those items on your list cause the pressure to fluctuate? At a constant idle the pressure was moving up and down about 2 or 3psi.

Maybe I just need some thicker oil and tell the guy to go trade it asap~! lol jk

[boostnlb7]

hahaha pawn it off eh.. you have to pull pan to get to oil pump..

[boostnlb7]

i just read back...im such a freakin retard!! sorry guys im out.. time for bed.. disregard my posts