New Guy With Oil Pressure From Bad To Worse!

[JB05Yukon]

Hello from Texas! I just picked up a really tidy 2005 Yukon XL with about 135k miles on a 5.3. The previous owner seems to have taken great care of it, with a log book full of regular oil changes. Paint and interior are immaculate for the age.

When I got the car, oil pressure was showing zero at all times. I figured it was the sender, and sure enough, I replaced this and started getting a reading. I then got low (10 psi maybe) at startup, but when driving I got just under 40. All along the car has had a faint but noticable knocking from the lifters.

I decided to go ahead with the pickup tube o-ring replacement to see if I could get it more consistently higher. When I pulled the pan, I recognized that somebody had likely done this fairly recently. The pan gasket looks fresh and the o-ring was red and flexible, not brittle or mis-shapen. Coincidentally the cross brace with the 4 big bolts that would normally block removal of the pan in a 2wd model is completely missing!

Anyway, I went ahead and replaced the o-ring and put everything back together, including a new filter and 6 quarts new 5w-30.

I now get a low oil pressure message and zero oil pressure on startup. This is accompanied by more noise from the engine. Naturally I haven't run it, just started twice and come straight to the forums.

Does this sound like the pump needs priming after removing the pan? I haven't messed with the pump. I'm reluctant to start the car or rev it until I have rectified this.

 

[SnowDrifter]

Only time the pump would lose prime is if you had it apart for inspection, replacement, etc. Anything that would dry the gears of oil.

You definitely made the right call by shutting the engine off. It doesn't take but a minute to completely ruin it!

As far as the low oil pressure, few things come to mind, in no particular order:

1. Wrong o-ring in oil pickup tube
2. Cracked oil pickup tube
3. Clogged screen
4. Bad oil pump. Doesn't happen often, but the gears can develop a crack. Especially if it was removed and reinstalled without shimming
5. Oil pump high pressure bypass stuck open
6. Obstruction in the oiling system. Like someone half removed the wrapper and installed the filter. That one's a pain in the ******* ass to track down
7. Cam bearings shot

 

[JB05Yukon]

Thanks Snowdrifter for the comprehensive reply. I’m sure I’ve got the correct o-ring and I’m certain I removed all packaging from the new filter. I didn’t pre fill the filter though (I never have).

I can’t rule out any of your other suggestions for the existing low pressure but I can’t imagine they’d have me go from ok to zero with the o-ring change?

I’m wondering if it’s even possible to have reinstalled the pickup tube badly? I didn’t really push the o-ring end into the pump housing I just put it in position Nan’s tightened the bolt and two nuts to “hand tight”. Could i possibly have messed this up so badly that I’m getting zero?

 

[JB05Yukon]

Ok, I’ve drained the oil again to remove the pan. After draining the oil, I removed the filter, and it is dry as a bone.

Should I have pre-filled it?

 

[Musicars]

I feel your pain. I have been dealing with a similar problem since April 2018. I have a thread under "oil pressure dropping". I am still driving my '06 with low pressure but have picked up a replacement engine . Just waiting for mine to go completely out or spring, which ever comes first. I have a few comments.
I never primed anything and never had actual zero pressure. I even took out and replaced the pump with a new Melling pump. I just filled it before I installed it (most rums out). There is a plug under the power steering bracket that can be pulled for priming but did not use that. I had pressure immediately upon start up although it was still low (10 at idle) which was what it was before the pump. so, I do not think priming is an issue.
I was wondering what you meant by hand tightening. All nuts and bolts should be torqued (I think 106 inch/pounds on the pickup to pump and 18ft/lbs on the pickup tube nuts). That's the only way to draw the pickup tube end into the pump. Sometimes the o-ring can get pinched. There are two to three different o-ring for these but it sounds like you know about that. The fact you had a dry filter makes me think the pickup tube is not inserted into the pump properly or the pickup is damaged and pulling it out made it worse. Also possible the pump is going out but that is rare.
I sent my oil out to Blackstone Labs and they found bearing material in it so I stopped diagnosing. You may save time by sending out an oil sample unless you got rid of the oil already. I have heard that the rear cam bearing can break down on these and give these results. For some reason I have come across this mostly in the 2005s and 2006s. I actually found some small metal particles in my pan.
Incidentally, I had my truck shipped up from Texas. Maybe it is a Texas thing.

 

[Lancem]

You have to seat the tube hard by hand, first time I did it I put it in place and thought bolting it up would pull it into place. Start up no pressure. Pulled the pan and seated the tube by hand, it sort of snapped in then all was good to go. If I were you I would look into replacing the missing frame member, it is there for a reason!

 

[JB05Yukon]

You have to seat the tube hard by hand, first time I did it I put it in place and thought bolting it up would pull it into place. Start up no pressure. Pulled the pan and seated the tube by hand, it sort of snapped in then all was good to go. If I were you I would look into replacing the missing frame member, it is there for a reason!

BINGO! Thanks for the replies everyone. I re-did it this morning; set the tube better, and filled the filter before installing. Instant oil pressure so I’m relieved. It’s about 20psi on startup now so hardly great but as the sender is at the top of the block I assume this is sufficient to keep it running long term.

 

[SnowDrifter]

Good deal!

20psi cold start is, however, still quite low IMO. I'm at 55 or so on a digital gauge at Start with 0w30

 

[HiHoeSilver]

Good deal!

20psi cold start is, however, still quite low IMO. I'm at 55 or so on a digital gauge at Start with 0w30

Agreed. A bit low still, but better than nothing. Curious why you run 0?

 

[iamdub]

I'd double-check that pressure with a mechanical gauge to rule out a defective sensor, especially if the sensor is an aftermarket brand.