2005 Yukon XL 6.0 low oil pressure problem

[W116_036]

2005 Yukon XL Denali 6.0 with 234,000 miles.

I'm having an intermittent low oil pressure problem with my vehicle and I'm not sure where the problem is at. Sometimes the oil pressure is good at 40 PSI or so at idle. But sometimes it drops to 5 PSI or so and the low oil pressure warning comes on. When the issue is present, the oil pressure slowly drops when idling until the warning comes on.

The car makes lifter noise when starting from cold for the first few minutes. Sometimes, but not always, it makes a ticking noise while driving at speed. So I'm not inclined to believe that it's a sensor or instrumentation error.

The car has always been run with Mobil 1 or Pennzoil Platinum 5W-30 full synthetic since we bought it with ~165k miles and changed before the OLM reached 0%. Since the issue came up, I added Lucas stabilizer (flame suit on) and it brought the oil pressure up enough to turn off the warning. Shortly after that I added Seafoam, drove around for 100 miles or so, and changed it again. The issue still persists and nothing ugly came out of the sump with the seafoam.

At this point I think my options are either: remove front timing cover and replace oil pump, or remove oil pan and check the pickup screen for debris. Both are labor intensive and speculative at best.

Any insight would be greatly appreciated!

 

[nwjones18]

Honestly before I went any further I'd double check the pressure with a mechanical gauge. I've seen vehicles that had good oil pressure with a lifter tick.. Just my 2 cents. Others will chime in that no better than I.

 

[Ojustracing]

I second that you need to verify the true oil pressure. Also there could be an issue with the Oil pump pickup o-ring and allowing it to suck air under certain conditions.

 

[addyguy]

The cheapest option is to change the oil to something thicker to see if it fixes the problem. At 234k, it is not unexpected to have a worn engine that has trouble holding OP - that is a lot of miles.

In TX, trying a fill of a 0W-40 or 5W-40 synthetic would not hurt anything. Or just try a conventional 10W-40 for 3-5k to see how it works.

 

[ls1mike]

A common failure at those miles on an LS motor is the oil pressure sending unit. It is located behind the intake and screwed into the top of the block.

The oil pump o-ring is a possibilty as mentioned but that is a pretty good sized job.

Verify with mehcanical if you can, but the Oil pressure sending unit is an easy swap.

 

[Nick1994]

Originally Posted By: ls1mike
A common failure at those miles on an LS motor is the oil pressure sending unit. It is located behind the intake and screwed into the top of the block.

The oil pump o-ring is a possibilty as mentioned but that is a pretty good sized job.

Verify with mehcanical if you can, but the Oil pressure sending unit is an easy swap.
This.

Replace the oil pressure sensor.

My mom's 2003 Buick Rendezvous had a low oil pressure warning a few times, replaced the sensor (they're like $10-$15) and it's been perfect.

 

[Ramblejam]

As the owner of one of these trucks, I'll join the chorus in recommending replacement of the oil pressure sender. Additionally, whether purchasing online, or at the local store, I'll suggest spending $10 more on the quality part (two-tiers available).

Originally Posted By: ls1mike
Oil pressure sending unit is an easy swap.


It's all relative, right?

Seriously though, tight access on these trucks precludes it from being a truly easy swap; then again, a little finesse is all it takes.

As for oil, it's time to step up the viscosity to xW-40.

 

[OneEyeJack]

Do the oil pressure stuff and then check back.

 

[joegreen]

I think i remember reading something about some issue with the oil pumps. I think it was that the valve that bleeds off pressure when the pump makes to much pressure gets stuck or something.

 

[CT8]

Agree with the check with a working gauge. Seems these days nothing is ever easy.

 

[demarpaint]

I would get an oil pressure reading from a mechanical oil pressure gauge. While I have the sending unit out I'd swap it for a new OEM unit.

 

[ArrestMeRedZ]

Wow, a bit of deja vu here. I had exactly the same problem with a 2005 C2500 with the 6.0 with about 115k miles. It was the wife's company truck, and while I can't vouch for the maintenance, I believe it was properly cared for.

I had to work at it, but was able to determine pressure at the sensor (on top of the engine, behind the intake manifold) was actually low. PITA to get to, connecting a separate gauge. As I remember, you had to hold your jaw just right to get the gauge threaded.

I replaced the oil pump, o-ring and made sure the pickup screen was clear. A bit of a task, as it required removing everything on the front of the crankshaft in order to remove the pump. Make sure you have the special crank pulley installation tool before you attempt this.

My "fix" didn't change a thing. I even checked again with the separate gauge. Sold the truck at a discount because of the problem. To my knowledge, it's run four years since then. Either that engine is indifferent to low oil pressure, or there was a blockage in the oil passage to the sensor.

 

[mjoekingz28]

Try PYB 10w-40 or look up D-Ray on the tube of you.

 

[W116_036]

Thanks for the replies.

I bought an oil pressure tester from Harbor Freight and removed the sending unit, but unfortunately this kit does not have the correct adapter for this engine. So I was unable to verify.

I'm not convinced that the problem lies with the pressure sending unit though because of the ticking and lifter noises. If the indicated oil pressure was low but the engine ran normally with no abnormal noises, I might be able to believe it's faulty.

New oil pressure sending units are absurdly expensive! $54 + tax from Autozoo, $101 + tax from the dealer, and $25+ online. It's a simple device, I don't understand why it's so expensive.

I drained the oil and stuck a scraper tool in the drain plug hole to see if there was any sludge but it came out clean. The pressure sending unit also came out clean when I removed it.

I'm at a loss as to where to go from here. I could pay to have the oil pressure checked but I don't think that would help. I could replace the oil pump *hoping* that's the problem due to faulty bleed valve or something. I just don't know.

 

[Ramblejam]

Originally Posted By: W116_036
I'm at a loss as to where to go from here.


Take a depth breath.
Exhale.
Relax.

The PS308 is $36 on Amazon. Stop fussing that they're not giving to you for free.

 

[Ramblejam]

Originally Posted By: ArrestMeRedZ
Either that engine is indifferent to low oil pressure


At operating temperature, allowable minimums per GM:

6 psi @ 1000 RPM
18 psi @ 2000 RPM
24 psi @ 4000 RPM

When up to temp (with 5w-30 in the sump), mine idles around the 4000 RPM pressure (which is normal for these), so there is a vast range of what's deemed acceptable.