Low Oil Pressure at Idle

[Nicolai8775]

So when I bought this truck, a 2004 z71 Suburban, I noticed the pressure was just a little bit lower than the "normal" pressure than on my old Tahoe.

I changed the oil and filter with Royal Purp 5w-30 and a WIX. It raised the pressure back up to where it should be. 40 at idle and 45-50 when I press the throttle.

I've driven 3,000 miles already cause I road tripped to Idaho. I'm assuming the oil is less viscous now, but the oil life counter on the dash says it's at 50%. At idle I get 25psi, at throttle I get maybe 40psi. I had read somewhere that it should be 10psi per 1000 rpm. If this is true I'm still in the acceptable range. But I don't like it cause it's not normal.

2 questions. Is this the O-ring issue on the pickup tube? Or could it be the rear main seal, I have some seepage on the backside of the pan where it meets the trans and some drips on the driveway. Does the rear main seal being broke affect oil pressure to the degree that I'm seeing? Maybe I have both issues.

I don't hear knocks, on a cold start I sometimes hear what I'm guessing is a lifter tick. It goes away within minutes of startup. I hope it's not a bearing lol

 

[Nicolai8775]

I see there are some other threads about this. Sorry for the repeat question lol. I guess I'm just curious about the rear main seal. I really don't want to drop the trans, I sold my jack.

I've replaced the oil pump and pickup tube before on my extra crispy Tahoe. It was a bastard to do cause of 4 wheel drive. I'm not looking forward to it lol

 

[Nicolai8775]

Interesting, this guy is saying the oil pressure sensor may be the source of my leak, it presents itself as a rear main seal leak.

 

[Nicolai8775]

Though my gauge on the dash isn't shooting to 80psi, it appears to be in working order

 

[OR VietVet]

I would change the sending unit and at the same time, attach a mechanical gauge to it and see what it reads. Especially since you had two different readings after the oil change.

https://www.rockauto.com/en/moreinfo.php?pk=8742996&jsn=1042 This is at RA

There is a way to see if the pickup tube o-ring is bad that involves over filling the oil by I think 2 quarts and then having the engine pointed down, lift in back with floor jack, and then run the engine and if the low oil pressure goes away, that means the excess oil covered where the o-ring is and was not sucking air.

I could be wrong so make sure you double check the other threads for that description of what to do.

 

[Nicolai8775]

I would change the sending unit and at the same time, attach a mechanical gauge to it and see what it reads. Especially since you had two different readings after the oil change.

https://www.rockauto.com/en/moreinfo.php?pk=8742996&jsn=1042 This is at RA

There is a way to see if the pickup tube o-ring is bad that involves over filling the oil by I think 2 quarts and then having the engine pointed down, lift in back with floor jack, and then run the engine and if the low oil pressure goes away, that means the excess oil covered where the o-ring is and was not sucking air.

I could be wrong so make sure you double check the other threads for that description of what to do.

I think I read that somewhere too. Now I do not have a liquid gauge, I only have a compression tester, can I make that work to check oil pressure?

By sending unit, are you referring to the pick up tube or the oil pressure sensor

 

[OR VietVet]

The sending unit is at the back of the intake, near the firewall, and that sends the signal to your gauge on the dash. The pickup tube is inside the oil pan and attaches at the motor with the o-ring in there. Your compression tester will not work for the oil pressure test.

With the questions you just asked, I am going to assume you are not that mechanically inclined. No slight intended, I am just making an observation. That sender is a turd to get to. If you don't have the know how, it is best to leave that to a professional. The rear main seal will not effect the oil pressure. That oil you see could also be a leaking oil pressure sender. Get a GM brand sender, like the one in my link.

Also, it is a sender and not a sensor. It sends the pressure reading to the gauge. Has also been called an oil pressure switch.

I do need to edit what I said about the rear main seal. If that seal blew out or was leaking fast enough, the loss of oil would have an effect on oil pressure. You would also stand a chance of blowing an engine. Hope that clears it up.

 

[Nicolai8775]

The sending unit is at the back of the intake, near the firewall, and that sends the signal to your gauge on the dash. The pickup tube is inside the oil pan and attaches at the motor with the o-ring in there. Your compression tester will not work for the oil pressure test.

With the questions you just asked, I am going to assume you are not that mechanically inclined. No slight intended, I am just making an observation. That sender is a turd to get to. If you don't have the know how, it is best to leave that to a professional. The rear main seal will not effect the oil pressure. That oil you see could also be a leaking oil pressure sender. Get a GM brand sender, like the one in my link.

Also, it is a sender and not a sensor. It sends the pressure reading to the gauge. Has also been called an oil pressure switch.

I do need to edit what I said about the rear main seal. If that seal blew out or was leaking fast enough, the loss of oil would have an effect on oil pressure. You would also stand a chance of blowing an engine. Hope that clears it up.

I know my way around these trucks, mostly. I didn't put it together that it "sends" the signal to the dash so it's called a sending unit. I understand now.

It's been dripping for a few weeks and the oil level is still in the dots on the dipstick. It is not leaking anywhere like my Tahoe was when it's rear main seal blew. In that truck it spit so much oil out it hit the hot exhaust when driving and made smoke. I'm hopeful it's the sending unit. It was pretty grimy/wet looking back there when I checked.

 

[Nicolai8775]

I'm the guy that made the burnt up Tahoe post a couple weeks ago. In that truck I did a cam swap, with push rods, new lifters, long tubes, tbss intake, leveling kit, new struts and rear springs, so much more. I've learned a lot. But there's still stuff I don't know apparently. Lol

I had put 40,000 miles on it with all the mods before it blew up

 

[OR VietVet]

The question about using a cylinder compression tester to check oil pressure is what threw me.

If that sender is wet, that is where to start.