Oil pressure

[Jeffdylanproctor]

I had a sudden change in oil pressure, and I'm debating if I should put a new oil pump in.

The truck was running at about 35-42 psi until about a month ago when it dropped to about 25-35.

When completely up to temperature, It cruises at about 30-35 psi, under acceleration it jumps almost to 40 psi, and if you let it idle for a while it will come down to 20psi.

The truck is a 2005 Escalade EXT with about 320,000 miles on it. I have another 2004 Escalade and its oil pressure is always about 35-42 psi (like this one was).

I just put a new oil pressure sensor in it this summer, and don't mind doing an oil pump job (I did one last spring in my wife's 2011 Escalade and it was pretty easy).

Thoughts on the oil pressure? Did the pickup tube o ring fail? Something else?

 

[Joseph Garcia]

I'd be more concerned about the 'sudden' drop in your average oil pressures. Your average oil pressures are a bit low, but not troublesome. A hot idle oil pressure below 20 psi becomes an issue.

I suggest that you perform the test for the bad O-ring in the oil pickup tube, as that could well be the cause of the 'sudden' drop in oil pressure.

 

[adventurenali92]

From what I’ve learned about these things is that there’s really only a handful of things that cause this scenario. While your oil pump could certainly be the culprit of low oil pressure, it’s more likely the pickup tube o ring. I’m not by any means a professionally qualified mechanic, but it would seem to me that if your oil pump is no good, you would not have ANY oil pressure at all…. But like I said that’s just me guessing.

My 2006 LQ4 6.0 Denali idles hot at 20PSI and will climb up over 40 or higher under heavy acceleration and at highway speeds. So your current pressures are not catastrophic.

Pickup tube o ring went bad on my truck in late March, and caused my oil to drop down to 10PSI idle and barely over 20ish under load. I had it replaced in June of 2020 after getting the oil leaks sealed up, as preventative maintenance as I know it’s a common failure point. Shop used the wrong o ring despite me bringing them the correct GM spec o ring for the pickup tube and it didn’t even last 50k miles. I’d be willing to bet that your pick up tube o ring is in its first stage of letting go given that you haven’t seen a HUGE drop in pressure but that you’re starting to see lower then normal pressure. Get a mechanical oil pressure gauge hooked up where that oil pressure sensor mounts and get a good read on actual pressure.

I also replaced my oil pump at the same time I did the pick up tube and o ring, but that’s because the timing cover had a pretty bad leak and it was easy to get it all apart at the same time as I was getting the oil pan underneath the timing cover opened up.poor timing cover gasket came apart into a million pieces as I got the timing cover off….. lol half of the gasket stayed on the block and the other half stayed on the cover….

Oil pump replacement for me probably was not necessary as I could definitely tell when I got the pickup tube out that the o ring was shot. It was loose and sliding all around the pick up tube instead of being firmly secure in the little notched bezel of the tube that it sits in to seal up. Showed the bad o ring to the two mechanics I’m tight with thanks to tons of detailing business I do with them, and both agreed that the o ring was the likely culprit in my scenario and that my oil pump probably was not an issue. Hopefully now with the fresh pump and o ring I won’t need to worry about oil pressure for a while haha.

 

[Jeffdylanproctor]

Thanks, I was just wondering if anyone thought it had got in the "danger zone"

I figured if it was anything it would be the o ring more than the pump itself.

I've got all the LS engine tools to get the front balancer off and everything, so might just go ahead and put a Melling 10295 pump in with a new O ring.

Is there a valve on the bottom of the pickup tube? Does it need to be replaced? Or is there just the pump itself? Hope I don't sound too dumb lol

 

[Joseph Garcia]

Replace the oil pickup tube O-ring and install an aftermarket fastener (Summit Racing) that improves the 'sturdiness' of the connection of the pickup tube to the block, by actually using 2 bolts to connect, while you are in there.

 

[West 1]

I think the first sign of a bad oring is slow pick up of oil pressure at cold start up. Once running they seal better.
Once they get worse sometimes it will not pick up oil pressure after start up or the delay gets longer.
You certainly may have a failing O ring.
Oil pumps are the best lubricated part in any engine and usually the very last part to wear out.
Sometimes dirt or particles can get in the oil pump pressure relief and cause pressure issues if the pressure relief piston gets sticky.

 

[B-train]

I had something similar happen recently on my 2008 Denali. Oil pressure dropped to below 20 after a highway drive when I got off for fuel. Left the truck running like always and heard a lifter start ticking.......on the way to a business travel meeting. Dang it!

I brought the throttle up to about 1500, the PSI was slow to respond, but eventually increased, and the lifter shut its yap....

The next day, oil pressue was 50 psi cold, and 35 hot. I asked my GM dealership friend about this and he said the pressure relief can get stuck in bypass, therefore dumping a lot of pressure. He said carbon/varnish buildup over the years can have that affect sometimes. He said put a quart of ATF in it before the next oil change and it'll help clean things up.

He also mentioned a machine they have at the dealership that flushes the motor with a 12 quart solution of high detergents through the oil filter housing and sucks the gunk from the drain plug hole. He used it on an old beater plow truck he had that had a lifter that started ticking (used, tired 454 from the 80's) so he flushed it and said it never made a peep after that. I found it interesting.

He also changes the oil in his stuff at 4k. He see so much damage/repair work from lack of maintenance. He's of the same mindset that oil and filters are cheap insurance.

Maybe this will help, maybe not. At over 300k, there are multiple possibilities of oil pressure loss. An almost instantaneous loss sounds mechanical to me vs a seal failure, but if that o-ring is original, that could definitely be contributing to it.

 

[2006Tahoe2WD]

Replace the oil pickup tube O-ring and install an aftermarket fastener (Summit Racing) that improves the 'sturdiness' of the connection of the pickup tube to the block, by actually using 2 bolts to connect, while you are in there.

FYI - I had the O ring replaced and attempted to install the Summit bracket. The mechanic said the bracket would not fit so just replaced the O-ring. Oil pressure resolved. I'm curious if anyone else got the "bracket" to fit.

 

[adventurenali92]

FYI - I had the O ring replaced and attempted to install the Summit bracket. The mechanic said the bracket would not fit so just replaced the O-ring. Oil pressure resolved. I'm curious if anyone else got the "bracket" to fit.

Interesting. I wasn’t aware there were any problems with how the pickup tube mounts to the block. And if I remember correctly my pickup tube already had two bolts that mounts it to the block and pump. I bolted the new tube to the block the same way the original one was mounted and hasn’t had any issues since.

 

[2006Tahoe2WD]

This non-stock "helper" bracket.

 

[adventurenali92]

This non-stock "helper" bracket.

No idea that existed lol.

 

[Joseph Garcia]

No idea that existed lol.

If you already had 2 bolts securing the oil pickup tube. that is unusual.

 

[LSCALADE]

Under certain conditions engine oil could shear out of viscosity due to the mechanical forces on the oil and its contamination with fuel and condensation so thats why when you run oil for a long time and you drain it, it appears to be as thin as water. I have noticed oil pressure increase on mine after every oil change and near the 4000 mile mark oil pressure starts to sag down and hit my alert limiter and thats how I know its time for oil change. Try some fresh oil and if it goes back up then that's your answer rather than a mechanical failure.