Low Oil Pressure diagnose
Thread Starter
TECH Fanatic
Joined: Jul 2022
Posts: 1,032
Likes: 389
From: Alaska
Low Oil Pressure diagnose Picked up a Denali, LQ4 runs good 215K miles, with VERY low oil pressure.
5 PSI idle, barely 20 PSI rev'd.
New Oil pressure sensor- same reading. The used take off oil sender works normally on a different vehicle ( ilde 35, rev'd 60+)
Swapped gauge cluster with known GOOD- same readings on Denali 5PSI idle.
Fresh oil, 7 quarts fill-- Oddly enough, the engine runs just fine and - amazingly makes NO clatter or knock, idle is smooth and quiet, runs great.
I guess we have three possibles:
1) Cam bearing walked itself OUT
2) Oil pump pressure relief valve fell apart
3) Pickup tube O-Ring failure
Proposed TEST for cracked or defective oil pump pickup tube O-Ring :
What if I over fill crankcase, Monitor oil pressure gauge ( at idle) while adding excess oil until O-Ring is submerged. IF O-Ring is leaking I should see an ABRUPT rise in oil pressure as soon as the O-ring joint is swamped in oil, right?
Question: How much oil, approximately , would this take? a Gallon over full? 6 quarts?
I can use low mile drain oil out of any of the fleet, so the experiment will cost nothing./
Is this a reasonable diagnostic tech?
5 PSI idle, barely 20 PSI rev'd.
New Oil pressure sensor- same reading. The used take off oil sender works normally on a different vehicle ( ilde 35, rev'd 60+)
Swapped gauge cluster with known GOOD- same readings on Denali 5PSI idle.
Fresh oil, 7 quarts fill-- Oddly enough, the engine runs just fine and - amazingly makes NO clatter or knock, idle is smooth and quiet, runs great.
I guess we have three possibles:
1) Cam bearing walked itself OUT
2) Oil pump pressure relief valve fell apart
3) Pickup tube O-Ring failure
Proposed TEST for cracked or defective oil pump pickup tube O-Ring :
What if I over fill crankcase, Monitor oil pressure gauge ( at idle) while adding excess oil until O-Ring is submerged. IF O-Ring is leaking I should see an ABRUPT rise in oil pressure as soon as the O-ring joint is swamped in oil, right?
Question: How much oil, approximately , would this take? a Gallon over full? 6 quarts?
I can use low mile drain oil out of any of the fleet, so the experiment will cost nothing./
Is this a reasonable diagnostic tech?
Joined: Apr 2006
Posts: 3,890
Likes: 1,137
From: Grand Rapids, Michigan
I don't know if the full size trucks have them, but I do know the Trailblazers and their clones are known to have relief valves that stick open. When I bought the Saab 9-7X that donated it's 5.3 to my Firebird, it had no oil pressure at idle and hardly any at higher RPM. Yet when I tore it down, the bearings all looked decent. If you do want to try the O-ring test, best thing to do is jack the back up really high so oil runs forward, and I'd guess you'd probably need 3 extra quarts with a truck pan to get oil over the pickup.
I once overfilled my C5 wet sump batwing oil pan looking for an issue. Used about 10qts of oil(!). It made no difference, and was a Helluva lot of work. Buy a Melling oil pump. That should take care of the problem. IIRC, and I may not, I seem to recall that around the MY 2000, GM had some issues with relief valves sticking. I've never had that happen, but the GM pumps seem to have a higher failure rate/relief valve sticking issues than the aftermarket pumps like Melling have.
NOTE!!!! If you do overfill, DO NOT rev the engine! You could blow out a seal or gasket somewhere. I really doubt it is the O-ring....
NOTE!!!! If you do overfill, DO NOT rev the engine! You could blow out a seal or gasket somewhere. I really doubt it is the O-ring....
Thread Starter
TECH Fanatic
Joined: Jul 2022
Posts: 1,032
Likes: 389
From: Alaska
Approximately + 10 quarts OVER the full mark on dipstick, backed up on a steep hill. nose down, at idle with 4 GALLONS of oil, I am getting 5 PSI gauge. Did not drive it much, just around the yard. peak15 psi at 3000 rpm.
Dilemma: Pull engine, or drop oil pan ?
Dilemma: Pull engine, or drop oil pan ?
Plan in replacing oil pump as first starting point. But before swapping pump while the pan is out take a flash light and look at the center cam journal to see if the bearing is shifted. If it's shifted game over theres your problem it's motor time.
If it looks ok throw new pump in it snug pan bolts up with 4 bolts at the corners dont even bother with the balancer fire it up and see what the pressure looks like. If its good your money drain oil drop pan and put it all back together completely with fresh gaskets and rtv the 4 corners.
If it looks ok throw new pump in it snug pan bolts up with 4 bolts at the corners dont even bother with the balancer fire it up and see what the pressure looks like. If its good your money drain oil drop pan and put it all back together completely with fresh gaskets and rtv the 4 corners.
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Plan in replacing oil pump as first starting point. But before swapping pump while the pan is out take a flash light and look at the center cam journal to see if the bearing is shifted. If it's shifted game over theres your problem it's motor time.
If it looks ok throw new pump in it snug pan bolts up with 4 bolts at the corners dont even bother with the balancer fire it up and see what the pressure looks like. If its good your money drain oil drop pan and put it all back together completely with fresh gaskets and rtv the 4 corners.
If it looks ok throw new pump in it snug pan bolts up with 4 bolts at the corners dont even bother with the balancer fire it up and see what the pressure looks like. If its good your money drain oil drop pan and put it all back together completely with fresh gaskets and rtv the 4 corners.
Now, maybe it would've thrown the rod anyway, IDK. All I know is the engine wasn't knocking and had good oil pressure before it didnt. No issues at all. As soon as that engine ran without the balancer, it was turned into scrap in less than 10 seconds!! Maybe it was coincidental, but the engine had no known issues before the balancer was removed. Talk about awesome toys, this guy had that Hemi orange Roadrunner for a couple of years, until it blew up. Bought it in 11th grade while living at home. So what does he do? He goes out and buys a 1969 427/435hp tri-power Corvette!!! Sold the Vette in 1981 for $4,000
Did I mention Bill never married??
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