Oil pressure/rebuild advice

[willfalcon]

I've read through a few threads with similar problems to mine, but these situations seem to be pretty case-by-case so I figured I'd go ahead and try to get some more specific advice.

I got this truck (06 Yukon Denali, 6.0) with over 200k miles, and probably drove it 40k over the last couple of years. It was my father-in-law's, and I know he did great with it on regular maintenance. I've always done regular oil changes, just going by the oil life meter, usually trying to beat it to 0%. I have been using Walmart oil and Fram filters though.

I ran out of air suspension problems to fix, so I turned to the engine... the pressure gauge had been pegged at 80 since I got it, so I got a new AC Delco original sensor and replaced it. That fixed the gauge, and for something like 5-10k miles, I didn't do anything else. The pressure would hang out at 20, hot or cold, and never really do anything else. I knew that was low, so I started researching and read about the pick-up tube o-ring situation. I ordered a new o-ring along with oil pan and cooler gaskets.

The day before I was planning on replacing those, (this was middle of October), I took it on a long drive, 2 hours both ways. This thing probably hadn't been driven more than 45 minutes in one trip since covid started. On the way back, as I stopped at the last stoplight in town before I got home, the pressure gauge dropped to zero and the dash showed a warning and dinged at me. That was the first time it ever did that.

The next day, I change the o-ring and gaskets, which actually stretched out over a couple of days. I cranked it up afterward and oil pressure went straight to 40. Great.

The next time I drove it for more than 20 minutes, it started. After 15-20 minutes of driving, when it's all good and hot and it can idle lower, oil pressure drops dangerously low, and it seems to have gotten incrementally worse over the last couple months. I got in a stupid situation last weekend where I ended up making that same 2 hour drive as before and it basically dinged at me the whole way. I'd constantly be shifting into neutral at stoplights to rev it back up. Even when at speed, 55mph going down a hill or something it'd drop down. I stopped to check the oil level after an hour or so of this and it was within the correct range, but on the lower side, so I topped it off with maybe 1/3 of a quart and it helped, but still dinged at stops.

So I'm basically convinced that it's just got bearings and whatnot worn down to where it won't hold oil pressure. I'm planning to get back under there and make sure I got that o-ring in there right, and then replace the oil and filter with something higher known quality. I'm also gonna look for a gauge to put on there and see what it says.

Is there anything else I should look into before I start trying to talk a buddy into helping with a rebuild? And then if it's gonna need to be a rebuild, what should I be prepared for with that? Never done anything like that. My friend knows what he's doing but I like to be able to pretend like I know more than I actually do.

Let me know what else you need to know and stuff

 

[exp500]

Trust but verify- Use a guage threaded into sender space, Also I believe there is a screen it the fitting you should replace. At least then you would know if guage readings are correct enough to plan your next steps.
You could even try the overfill to see if pressure runs stable there. Keep posting results, good luck hope its an easy one.

 

[JonnyTahoe]

If your talking about the Oil Pump O-Ring that you had to removed the Oil Pan to replace and spent hours putting it back together how could it not be installed correctly.

 

[willfalcon]

Trust but verify- Use a guage threaded into sender space, Also I believe there is a screen it the fitting you should replace. At least then you would know if guage readings are correct enough to plan your next steps.
You could even try the overfill to see if pressure runs stable there. Keep posting results, good luck hope its an easy one.

Yeah certainly going to check it with a gauge before I do anything drastic... I'm worried about running it overfilled long enough to get the oil hot to see what happens. I know overfilling is bad, foamy oil, etc. Would letting it idle like that for 30 minutes do any more damage than what's probably already been done?

If your talking about the Oil Pump O-Ring that you had to removed the Oil Pan to replace and spent hours putting it back together how could it not be installed correctly.

Indeed it did take hours. Not exactly itching to do it again... I read elsewhere that you have to get it really seated up in there... Somebody said they got the tube shoved in there enough to where it would hold itself up before he bolted it down. That definitely wasn't the case with me... I got it in there but I could still see the o-ring seated there as I held it in place to bolt it back together. It all lined up straight as I did that, so I thought I had it right at the time, but I wonder if I really didn't have it seated right and it's fallen slack and lost the seal since then.

 

[willfalcon]

Trust but verify- Use a guage threaded into sender space, Also I believe there is a screen it the fitting you should replace. At least then you would know if guage readings are correct enough to plan your next steps.
You could even try the overfill to see if pressure runs stable there. Keep posting results, good luck hope its an easy one.

Also, mine doesn't have that little filter, checked for it yesterday. I think I remember reading that they stopped putting them in at some point. Could definitely be wrong about that, if anyone knows better.

 

[Just Fishing]

My hoe had that problem after having the trucks nose in the air on jack stands for some transmission work.
I had run some seafoam on this new to me hoe prior to that.

Sudden drop in pressure afterwards. super weird.
I did the o ring replacement, huge pita.

Result = no change.

I did find a bunch of sludge that i had knocked loose in the pan, figuring i sucked up some crud and it went right into the bypass.

So i decided if I'm doing it again, then I'm doing the lifters, cam, cam chain, and oil pump.
(deleting that AFM system while i'm in there, plus i can tune my self)

I'm still in the process of getting it running again, but i did find that the bypass in my oil pump was stuck open slightly.
Removing the bypass i found grit.
Cleaning and reassembling it was clear the bypass piston seated all the way into the bore.

At this point I'm feeling pretty good that this was the cause...


Also one sign i had was a lag with the pressure rise when i revved the engine.
Part of why i thought the bypass was part of the issue

Food for thought.

 

[clandr1]

You mention the truck dinged at you and the light came on, but did you hear the engine ticking/clicking while at a stop, at idle? If not, you may not have an oil pressure issue - it may be a bad sensor or bad gauge. I second the suggestion to get a mechanical oil pressure gauge and confirming if you actually have low pressure or not.

I have 222k on my motor, and the only issue I had was resolved about 3 years ago by replacing the pickup tube o-ring. I could CLEARLY hear ticking/clicking noise at idle which is how I knew I had an issue.

 

[willfalcon]

I'm still in the process of getting it running again, but i did find that the bypass in my oil pump was stuck open slightly.
Removing the bypass i found grit.
Cleaning and reassembling it was clear the bypass piston seated all the way into the bore.

Hmm. Sounds worth checking into... I’m not sure I know of this bypass though. It’s part of the pump assembly? Any advice/resources to help me check that out?

You mention the truck dinged at you and the light came on, but did you hear the engine ticking/clicking while at a stop, at idle? If not, you may not have an oil pressure issue - it may be a bad sensor or bad gauge. I second the suggestion to get a mechanical oil pressure gauge and confirming if you actually have low pressure or not.

I knew I was forgetting a chapter in my novel.... I did have some pretty solid ticking until I did my o-ring, and it disappeared after that. Still not getting it at all now even with the constant pressure issues. On the dash. Not sure if it’s anything but when i get a warning, there’s no actual light, just the “low oil pressure” message on the little message reader thing and a dinging that stays until I get back on the accelerator and it goes back up.

Say I put a real gauge on and it reads fine... what would I do at that point? Swap out another sensor? Start chasing wires around for a short of some kind?

 

[Just Fishing]

the bypass will be on the bottom of the pump
the issue, the pan and the front timing cover must come off.

The bypass is a little plug with a Hex socket.
Removing that plug, you will find a spring, and at the top of that spring a little piston.

 

[iamdub]

Hmm. Sounds worth checking into... I’m not sure I know of this bypass though. It’s part of the pump assembly? Any advice/resources to help me check that out?



I knew I was forgetting a chapter in my novel.... I did have some pretty solid ticking until I did my o-ring, and it disappeared after that. Still not getting it at all now even with the constant pressure issues. On the dash. Not sure if it’s anything but when i get a warning, there’s no actual light, just the “low oil pressure” message on the little message reader thing and a dinging that stays until I get back on the accelerator and it goes back up.

Say I put a real gauge on and it reads fine... what would I do at that point? Swap out another sensor? Start chasing wires around for a short of some kind?

Before you drop the pan again- check the pressure with a mechanical gauge. It's possible you have a faulty sensor. Even more possible if it's a cheap store brand, particularly Duralast from AutoZone. Or, it's not the sensor's fault at all and you could have a gunky oil system that may have partially clogged the sensor, making it sense lower than actual pressure.

Also, stop using Fram filters unless they're the Ultra Synthetic (gold filter) and stop going by the Oil Life Monitor unless you're running quality synthetic oil. If running cheap oil, stick to a more regular oil change interval, like 5,000 miles or so.