Oil pressure loss and hybrid mode

mtown27

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I've got a 2008 Hybrid Yukon with 190,000 miles on her. She's recently started to have oil pressure issues on the gauge dropping below 40 at idle, and RPM drops below 1000 with a rough idle. I changed the oil pressure sensor behind the motor in 2015 but didn't know about the screen (didn't change it). The oil pressure is hit or miss. Sometimes the motor runs great all day, always going to Autostop at red lights and low speeds, and other times the oil pressure is always at or below 40 on the gauge. I did an oil change 500 miles ago with 5W-30. I'm stumped on what it could be. Plugs are relatively new and clean. Oil pump going bad? I've seen others pull the pan. I've also seen someone post about a 2nd sensor on the side of the oil pan. The rough idle and not going to hybrid is eating me alive!! Any thoughts?
 

lt1gmc

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Seems some with miles on them have had an issue with the oil pump relief valve sticking and bleeding oil pressure off when it sticks in bypass mode. That could explain why it is good sometimes and not others. Best to hook up a mechanical gauge to prove it is oil pressure or an electrical issue with gauge or wiring.
 

Johan

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When mine is hot, the oil pressure is always around 40 psi. The car works perfectly and the engine is incredibly soft. In the instruction it says that the pressure should be over 29 so just under 40 should not be any problems?
 

mtown27

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I bought the truck in 2012 and the oil pressure was always constant at the right needle mark. It stayed that way for 4+ years until recently. Now it flutters and drops way below 40 at idle. During normal driving it will go right back to the right needle mark. At idle it drops below 40 again. I’m changing the oil pump soon. Could be the pressure relief valve, could be something totally different. Trying to avoid an engine rebuild at 200,000 miles but it wouldn’t hurt.
 

MPAWill

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My first post. I gave up on forums 5 years ago but im back because I may be able to help someone lol

I have a 09 hybrid tahoe 110k and I had oil pressure issues. Had!

1st. Oil pressure was on zero, Guage on zero didnt move. No check engine light. Fix: changed oil pressure sensor.

2nd (1year later) low oil on dtc, Guage on 20 and below. Oil in motor. Stealership said head gasket and wanted 6.5k(another story) i changed oil, filter, oil pressure sensor, sensor filter, with no change. Read on one of the forums the pick up tube o ring goes brittle and sucks air and oil which leads to low oil pressure readings so I changed it.fix: oil pickup tube and oil pan gasket using the instructions on a Cadillac Escalade someone posted and as of the last 4 weeks oil pressure is back above the center needle and idling like a brand new truck. hopefully this helps this gave me nightmares but everything is back to normal now. I literally thought I was going to have to sell my truck which I didn't want to do but I fixed the issue Feel free to ask any questions you need to I know the process inside and out

Will
 

jprevost

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Check that adding oil doesn't fix the problem. I have a cracked oil pick-up tube o-ring that has caused this same issue. Because it's a 4x4 and because they didn't design the pick-up tube flange to be bolted from the front, it's very difficult.
Good luck.
 

dnt1010

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So jprevost are you saying that if you suspect the oil pickup tube o ring is leaking that that you can overfill the oil level to test? On the 6.0 is the oil pump at the front or rear of the engine? and is it positioned on the drivers or passenger side? I am thinking that overfilling and parking on a steep sideways slope at just the right angle might cover the top of the pickup tube oring and prove or disprove a bad oring? Brilliant man just Brilliant, you got to love these forums they are just full of awesome ideas
 

BG1988

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I've got a 2008 Hybrid Yukon with 190,000 miles on her. She's recently started to have oil pressure issues on the gauge dropping below 40 at idle, and RPM drops below 1000 with a rough idle. I changed the oil pressure sensor behind the motor in 2015 but didn't know about the screen (didn't change it). The oil pressure is hit or miss. Sometimes the motor runs great all day, always going to Autostop at red lights and low speeds, and other times the oil pressure is always at or below 40 on the gauge. I did an oil change 500 miles ago with 5W-30. I'm stumped on what it could be. Plugs are relatively new and clean. Oil pump going bad? I've seen others pull the pan. I've also seen someone post about a 2nd sensor on the side of the oil pan. The rough idle and not going to hybrid is eating me alive!! Any thoughts?
MAF dirty/bad air filter issues . crappy gas. it's not upto par try. shell mobi or cheveron
could even be a vacuum leak
as per the user manual
Oil pressure should be 29 to 80 psi (200 to 550 kPa). In certain situations, such as long extended idles on hot days, it could read as low as 15 psi (105 kPa) and still be considered normal
 

dnt1010

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OP does not describe exactly how low the Oil Pressure drops but if it is just a little lower than normal with a rough (slow) idle speed that kind of makes sense. A lower rpm will equal lower oil pressure. Sounds like it could just be an ICE problem. Maybe a good tuneup fixed him up?
 

tiktok4321

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So here are a couple of things that I went through recently (over the past 2 years) with my 08 Tahoe Hybrid. The AFM (Active Fuel Management system which hydraulically disables 4 cylinders while cruising) is notorious for causing the lifter casing to crack then the lifters themselves sticking. This results in worn cam lobes. This results in your valves not fully opening, which causes misfires. I paid a local guy nearly $4k to do a full top overhaul, replacing the camshaft, lifters, head, gaskets, plugs and wires. I did that over a period of 3-4 months, $1,500 at a pop because he was incompetent.

Eventually it ran fine for nearly a year and a half. Then, I started losing a quart of oil every month. Different mechanics suggested that I just replace with a quart of Lucas. Then, last Thanksgiving, I was driving my family up to Tennessee. Oil pressure started dipping to around 20 PSI and started dropping slowly. I got a warning that oil pressure was low. I stopped and bought a couple quarts of oil. Kept going for another 200 miles. Oil pressure dropped again. Made it to Tennessee when the check engine light started flashing. Pulled off the highway in Chattanooga to get a code read from Autozone. But by then it was too late. Engine started knocking real bad. We limped to a dealership.

Long story short - Dealer took $6500 to replace the engine with a reman. 100,000 mile, 3 year warranty. Better than most used cars. Immediately, though, I've noticed that when running in V4 mode - sometimes - it vibrates just a little more than it does in V8 mode. That concerns me.

Less than a week after the engine swap, oil gauge started acting erratically. New engine, same bad oil sensor. Replaced that. No problems since (except the periodic V4 buzz).

Moral of the story - it could be a bad engine, caused by their faulty AFM system.
 

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