Drop in oil pressure

[mtown27]

I posted this in the Hybrid forum but havent had any luck. Id imagine this also applies to non-hyrbid trucks as it is only an issue when the engine is running.

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 with a rough idle. I changed the oil pressure sensor and screen behind the motor in 2015. 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. Engine seems to run better when the outdoor temp is below 85-90 degrees, anything over that and the oil pressure is an issue. 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?

 

[JDC81]

synthetic oil or std? the oil may be thinning out too much in the heat if its regular.

 

[mtown27]

Synthetic. Im thinking about replacing the oil pump with the HV unit and changing the oil pickup tube o-ring. Will the weak oil pump cause the engine to shake a bit and run rough when the oil pressure drops low? I know the AFM is a huge issue with these motors.

 

[mtown27]

What's the range on the oil pressure for these trucks? I constantly run around 60, and when the truck runs poorly, at or less than 40. At start up it instantly goes to 60 and holds. Holds at 60 while I'm driving. When the temp outside is hot, the oil pressure drops to 40 or below and the motor runs poorly. At that point, the motor hesitate on acceleration and has a rough idle, sometimes a spike in RPM. See pictures below.

 

[mtown27]

Anyone have any advice on the random low oil pressure?

 

[swathdiver]

Not familiar with your motor, has it always run at 60? Are you the original owner? My 5.3 idles around 20 and is usually just north of 40 underway, all normal.

 

[mtown27]

2nd owner. I've had it almost 5 years and it's ALWAYS run at 60. Drops to 0 when it goes into auto-stop. Goes back to 60 during any drive or idle. Now it runs rough around 40 and won't go into auto-stop if it's around/below 40. It has a jerk/hesitation when it runs at 40 and at idle.

 

[swathdiver]

Well, hopefully someone familiar with your engine will chime in soon and help out.

 

[Danny3737]

It could possibly be a bad sending unit that starts to fail when it gets hot.

 

[mtown27]

Isn't the oil pump mechanical and not electrical? How hard is it to swap the oil pump?

 

[Maximus1]

You should buy this and deactivate the active fuel management. It's crap and causes everything from low oil pressure to oil consumption and several other problems. Your problems are only going to get worse until you do or you'll probably be replacing the engine.
https://m.summitracing.com/parts/cmb-09-0030

 

[ta08hoe]

I think the running rough and rpm drop is causing your oil pressure to be a little lower than normal I doubt there is any problem with your oiling system if its just under 40 that's still pretty healthy obviously the higher the rpm the higher the pressure! Is look into coils possible fuel filter tune up stuff

 

[rook]

Sounds like when my oil pickup grommet went out. I have a thread on here somewhere. When it goes, it is just rubber - after years of heat it turns to more like plastic and breaks into pieces... when oil is cold or at high revs enough is flowing to give you some pressure, but when you get heated up and come to a stop, drops significantly. Cheap fix, dealership and mechanics won't even talk about it because isn't an expensive part or real difficult fix.


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[mtown27]

Thanks. Gotta pull the front out and replace the grommet, or pull the pan and do from below?

 

[rook]

Pan. To get my pan down I had to pull a lot of stuff: front crossmember, diff, steering, etc. if you could get your pan off without taking a bunch of stuff off, you're luckier than I. It's like a $5 part but a bunch of big bolt stuff to get to it.


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[Buzzcut]

10 psi per 1000 rpm was rule of thumb on oil pressure

 

[mtown27]

Pretty easy to do. Took about 3-4 hours total. Crossmember, air deflector and one bracket was all I had to remove. O ring was pretty flat, but it seems to run much better now. Hybrid works now like the day I bought it.

 

[rook]

Pretty easy to do. Took about 3-4 hours total. Crossmember, air deflector and one bracket was all I had to remove. O ring was pretty flat, but it seems to run much better now. Hybrid works now like the day I bought it.

Right on. It makes no sense to me how much havoc that little grommet causes when you lose pressure. When mine went there were a couple other warning lights that went off, I think stability control, CEL, low oil. That fixed it all.