Major Oil Leak

[Thomas Hennigan]

I've got a 2002 Yukon Denali with 274k on the clock. It's been leaking oil for 60k miles but I've kept it in check with StopLeak products. However, now when I run the highway at 75+ mph I lose significant amounts of oil, like a couple quarts on 60-90 roundtrip. From the threads on this forum it could be:
Valley pan gasket
Valve cover gasket
Rear Main seal
Oil pressure sending unit
Oil pressure block off plate
Oil pan gasket
Oil pressure sensor

It's beyond StopLeak, I gotta do something. The dealer didn't want to touch it. My longtime guy said it's a rear main seal, but he's old and can't handle it. The third mech wants to start up top w valve cover gaskets and oil pressure switch.

Is a leak of this sicope most likely a rear main problem?

 

[OR VietVet]

Impossible to say. Adding StopLeak and not fixing for 60k miles and now you have oil all over the place on the outside. IMO, pressure wash the entire engine and add dye and drive and see where the dye shows up at. If leaks that bad, it may not even need the dye to pinpoint. Rear main seal is a likely spot but then the oil showing would be confined to that area.

 

[rockola1971]

As PNW said...clean the engine of all old oil grime first. Then snug the valve covers and the oil pan then drive it and see where the oil is at.

 

[Kman]

Years ago I had this issue on my 5.3 2001 Tahoe. Couldn’t tell where the oil was coming from but it was a lot. Took it to one of the best shops in Orange County and they insisted it was the rear main seal. I told them to start with the oil pan gasket but nope they said rear mail seal. So I spent the money and they did the rear main seal. A week later there was an oil spot in my driveway. Finally convinced them to change the oil pan gasket and the motor hasn’t leaked oil in 120,000 miles.

This is just my own personal experience. Start with the easy and most common, I would say replace the oil pan gasket first! Good luck!

 

[89Suburban]

I would say rear main would be the least likely on your list but that’s just my humble opinion.

get a light and mirror or an inspection camera and try to look at the rear top of the motor for leaks at those gasket points.

 

[OR VietVet]

I have never seen excessive oil leaks from a rear main seal, except for one time where a shop had fixed one, car came in to my shop and the new seal had blown out because it was not installed properly. The oil pan is a larger surface area, around the edge, that can leak a larger amount.

 

[mattt]

One more that I've heard can be a source of a hard to find leak is the cam position sensor. It is located next to the oil pressure sending unit on the back of the block. It leaks down internally and gives the appearance of a rear main seal leak, because of where it is located and where the O-ring seals inside the block. I believe the O-ring is not available separately though.

Additionally heard the same possible leak source for the crank position sensor which is above the starter on the side of the block. That one is easier to see from below. The cam position sensor leak can't be seen without removal of other things.

Let us know if and when you locate the leak source.

 

[Thomas Hennigan]

We snugged the valve covers and replaced the oil sending unit. Next up is the oil pan gasket and Rear Main Seal. Is there anything else I should get done or replaced while I have the drive line apart ? Are any of the following easy replacements while the rear main repair is underway...

Valley pan gasket
Valve cover gasket
Rear Main seal
Oil pressure sending unit
Oil pressure block off plate
Oil pan gasket
Oil pressure sensor
Cam position sensor
Crank position sensor

 

[smcnair]

When you do the oil pan gasket go ahead and replace the o-ring on the pickup tube as it is a failure item.

 

[89Suburban]

When you do the oil pan gasket go ahead and replace the o-ring on the pickup tube as it is a failure item.

And the oil splash shield thingy.

 

[Fless]

And the oil splash shield thingy.

If that's the AFM shield there shouldn't be one needed on a NBS engine.

 

[89Suburban]

If that's the AFM shield there shouldn't be one needed on a NBS engine.

That's a good thing then!

 

[Kman]

Clean the oil off everywhere that you can. Replace just the oil pan gasket and the other items like the pick-up tube o-ring when you drop the pan. When it's simply the pan gasket and I save you a huge headache you can thank me later. haha

I felt so dumb when my Tahoe was leaking oil and I couldn't figure out where it was coming from and neither could two shops. Someone on here years ago said oil pan gasket and sure enough that was the simple fix.

 

[Thomas Hennigan]

The shop also replaced the "oil cooler lines" which were badly leaking. This all seems to have cleared up most of the leak. It's still spotting, but not puddling, and not consuming 2 quarts on a 60 mile roundtrip. After cleaning up the engine and doing the other work, it appears there is a small leak from the oil pan gasket. Not sure why they didn't also do the oil pan gasket when they replaced the oil cooler lines. I assume the tech didn't think it was worth it to do the oil pan gasket. Thanks for everyone's help. We'll leave the rear main for another day.

 

[OR VietVet]

That oil pan gasket would be a lot more labor to do it. Maybe he was feeling lazy and did not ask you, or he was not sure because of all the other leak. The spotting you see could still be old oil dripping off from other spots other than the engine. You can re-tension the bolts on the pan and that may slow it down or stop the leak. Be careful not to over-tighten and crack the oil pan.

 

[mattt]

With how many oil leaks these things have and how many NBS trucks and SUV's I see on the road, I'd bet there are plenty of GM's running around leaving their mark with oil and lots of well oiled -never to rust- undercarriages. For anyone that's BTDT, have you come up with a clever way to clean the undercarriage of all the oil that's all over?

The thought of getting on a creeper and cleaning up undercarriage by hand is not feasible. There is the quarter car wash option, but unless you have a substantial suspension lift, getting the spray wand all over is also not going to be super successful. Anyone ever seen or heard of a business that does undercarriage clean up?

Adding this to this thread since it's related content (cleaning up Major Oil Leak) and I have a bit of a mess on the under regions and will be swapping engines in the next month in my Tahoe. Thanks all.

 

[OR VietVet]

You can rent or borrow a pressure washer and lift the rig and put on tall jack stands. I have done it and seen it done. Depends on how bad you want to clean under there.

 

[Thomas Hennigan]

You can rent or borrow a pressure washer and lift the rig and put on tall jack stands. I have done it and seen it done. Depends on how bad you want to clean under there.

So, I got the truck back and now the A/C is blowing hot. WTF. Could anything the techs did effect the A/C system?

 

[OR VietVet]

Got the truck back, like in post #14 on Monday and just noticed today about the a/c or is the truck back from another trip to the shop? Confusing?

Did you check to see if the a/c compressor is even engaging or is not? Check electrical connections at the compressor and at the lines and accumulator.

 

[Thomas Hennigan]

Got the truck back, like in post #14 on Monday and just noticed today about the a/c or is the truck back from another trip to the shop? Confusing?

Did you check to see if the a/c compressor is even engaging or is not? Check electrical connections at the compressor and at the lines and accumulator.

The compressor wasn't engaging. I opened the fuse box and strangely, the fuse for the A/C was ajar in the fuse box just sitting on top of the fuse block not quite pushed in. I pushed it back in and presto.... Cold A/C. Thanks. More strangely, I can't get the $40 can of A/C Pro that i bought to recharge the system to work. Followed the directions but the digital gauge doesn't seem to be working. Some refrigerant went into the system because the can got cold and you can tell its a little lighter but I dont wanna overfill. I'll take it back to Advanced, maybe get a gauge. Thanks again for the help.