Oil Leak possible oil pan gskt?

b00001

Original poster
Member
Feb 18, 2019
3
Colorado
2004 GMC Envoy XL 5.3, 4wd

I just picked this Envoy up, runs perfect, clean, 170k miles. Looks to have been leaking a very long time.

I am having a heck of a time chasing down this leak and at the end of my rope. Thought I would throw it out to you all, see if there may be something that I am overlooking.

I am getting a good bit of oil each night, or anywhere I park for a few hours time. It is a sizable puddle, well more than just a couple drops here or there. The entire oil pan all the way to the bellhousing is covered in oil. I have degreased the pan and surrounding area as best as possible in order to isolate the leak. The best I can tell it is the oil pan. The oil pressure sending unit has been replaced, I was hoping that would cure the leak. Nope. I also did valve cover gaskets and grommets.

After cleaning it up and letting it run I could see oil dribbling out from what appears to be the oil pan gasket (above the bolts in the picture). I was able to get a wrench on most of the oil pan bolts, all were snug on this side (driver side), but I could not reach the bolt that is located above the differential. I am wondering if that one is loose causing the leak.

On the passenger side, I did find one bolt that was literally FINGER TIGHT. I snugged it back down and so far, no oil from the passenger side.

Any ideas? I looked up how to pull the oil pan and damn!!! Looks to be a full day job. I really do not want to get into it that deep as it will likely cause more problems and from what I have heard, these oil pan gaskets are well made, riveted into the pan and rarely leak.

Thank you all in advance!87641
 

Reprise

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Jul 22, 2015
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Hello from a fellow 5.3 owner! You've done pretty good so far with the OPS and valve cover gaskets. "Start from the top and work your way down", as I was advised by my local mech when he tracked down an oil leak issue I had in one of my Sierras.

Since you have an '04, there should've been a PCV valve at the back of the driver's side valve cover. That's a potential leak source, if the valve clogs up.

The one place you didn't mention was the front / rear main seals. For the rear, there's an inspection cover in the bellhousing that you can remove (round, twists off via slots). With it off, you can get one of those USB borescope cams in there and examine the area where the flexplate bolts up to the engine. If it's contributing to that leak area, you should be seeing a lot of oil there, given how much you're describing seeing in the surrounding area.

The front seal is harder; you'll have to remove a bunch of stuff to get to it (basically, the entire front of the engine.) Thankfully, the front seal gives out at about 1/10th the rate of the rear one (the cant / angle of the engine is a big reason why the rear one leaks more.)

I'd guess that unless you see a bunch of oil at the front of the pan / around the front cover, that the chances of the front seal giving way are slim. IIRC, two bolts at the front of the oil pan are part of the front cover area (they're longer). That can be a source of leakage (more so than the front crank seal, TBH)

I wasn't aware that the LM4 had a riveted pan gasket. I know the 6.0L trucks do, but didn't know of any 5.3L engines (especially ours) having that (I may be wrong).

BTW...The area centered by your pic happens to be a boss for an oil cooler setup (not in our trucks). That's another prime place to look on the 6.0L-equipped trucks. In your case, the send / return outlets are plugged off, and you can see there's no leakage.

While I haven't done this in mine, you might try a crowfoot w/ extension for that bolt above the diff. Barring that, you may be able to loosen but not fully drop the diff (of course, there's a lot of work that goes in before that, including disconnecting the axles from the hub / knuckle (at a minimum), so that the diff can drop down. And you'll need to disconnect the front driveshaft, too. A big job, as you say. If you actually get that far, I'd probably just go ahead and replace the pan gasket, outright.

Now that you've got all the other bolts snugged up tighter, clean the area and see where you're at. Another option is draining the oil / refilling it, and run the engine again to let the oiling system pressurize - if you cleaned off the areas good enough, there's a good chance you'll see the seepage beginning anew out of anything that's still allowing oil to leak through. This method helped me figure out that my cooler gasket on the Sierra needed replacing.
 
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Mike534x

Member
Apr 9, 2012
894
Your oil leak sounds worse then mine. I usually have a couple drops from where I park, unfortunately for me its a combination of the rear main seal AND the front differential seal for the passenger side CV joint. I'm looking to spray mine down this summer and see if I can tackle one of them (probably the differential, don't have the know-how of doing the rear main). Though I should be thankful, the oil coating the front underside has kept most of the components and frame rust free, so it does have its benefits. :2thumbsup:

Like Reprise said, I would check the PCV for a blockage. I don't believe they were interchangeable in that year so you would need the updated valley cover if thats the case (about a 10 min job)
 
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Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
There are UV dye kits that you can add to the oil and look for the leak using a UV light. That could help pinpoint the leak. You would have to clean everything down first though.
 
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b00001

Original poster
Member
Feb 18, 2019
3
Colorado
Reprise- Thank you very much for your in depth thoughts! Front of the engine is clean, therefor I ruled out frt seal. (I was looking into possible steering pump leaks as well) I did pull the inspection covers (round) at bottom of bellhousing and it looked to be dry inside. I do not have a scope, but I did use a mirror. I also removed an inspection cover at the front of the bellhousing, the plastic one on the side, put mirror up there as well, flywheel dry and as far as I could see, dry inside. It pretty much has to be the oil pan gasket then correct?

If I do wake up one morning full of energy and vigor (highly unlikely) are there additional seals that need to be replaced when removing CV axles and diff?

Thank you all for your insight, and Moose- I was thinking about the dye as well but I can clean that area in my pic, start the truck and it seems to come out of the corner of the oil pan gasket area right above the oil cooler line block off.

Oh and Mike534x-- The job of removing the oil pan looks to be about as in depth as splitting the trans. If you are going to do the diff, I would have confidence that you could do the trans. Good luck on your project.
 

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