2001 Chevy Tahoe Engine Oil Leak Help

[Allende]

Hi folks. I'm new to this site and new to DIY maintenance on my '01 Chevy Tahoe with ~190k miles.

I've got a very slow engine oil leak. I noticed a few drops on the garage floor the other day and found a drip on the drain plug, as well as on the bottom of the filter, and oil staining on the rear part of the pan. I did a bit of online research and thought this could be oil pan gasket or rear main seal leak. The leak is very slow - minor drop in oil level over a month plus.

I bought some fluorescent dye and put it in the engine oil. I then drove the car on normal city duty for ~100 miles and checked for fluorescence with a blacklight. The fluorescence showed up as expected, confirming an engine oil leak. The fluorescence seemed to be most concentrated just ahead of the transmission bell.

Attached are several pictures showing the leak (using camera flash) along with several showing the fluorescence. Apologies for the crappy camera phone images.

I'm looking for some advice on what exactly I should be looking for to confirm the root cause. Can anyone recommend next steps for diagnosis or what else I should be looking for? Is this a oil pan gasket leak or something more serious?

Many Thanks!

 

[bottomline2000]

Rear main seal more than likely. Very common on these trucks. I had mine replaced when I had transmission work done and then did it myself on the new motor. Part is not expensive, it's the labor to get to it..have to drop transmission and remove flex plate to get to it.
I would check the oil pressure sensor too. It's on the top rear of the motor, just behind the intake.

 

[Bigbertha78]

I would swap the oil cooler block of seal and check the oil pressure sensor first before going with the rear main seal. Looking at the dye, it looks to be no higher than the block off plate. The oil cooler block off seal is around $3 at a parts store and it's two bolts, throw a little black sealant on just incase too. Changed mine when I changed the oil, super easy and cheap. Here's the one for my 2004.

 

[treehan77]

Mine seems similar. If I clean everything up and run it on ramps, I can see oil collecting in the inside starter bolt. I changed out the oil pressure sender, no change. Gmc tech diagnosed as main seal, he thinks it's slinging it up top. Inside the inspection cover is bone dry. Guess I'll just live with it until I need transmission work, as they want over a grand to fix it. That does include a small oil pan leak as well, which is aggravating because that was already changed less than 5k miles ago

 

[electro]

Are you sure it's not coming from above rear main seal? Something higher up?

 

[treehan77]

Are you sure it's not coming from above rear main seal? Something higher up?

I am not sure. But it is definitely not the oil pressure sender, tried that. Not sure what else it could be. The mechanic did show me my rear main looked bulged out near the top, seemed legit. I guess it could be something else but what. I wouldn't know unless i took off the manifold etc. it's not valve covers.

 

[treehan77]

Thought about changing the o ring on the cam position sensor, thought about crank position sensor. Decided not to do anything so far lol as it seems to leak down both sides after a while. First visible in that starter bolt, so who knows, maybe it blew back up on top of the oil filter. Mine def doesn't appear to be leaking at the block off plate (I don't have oil cooler). I suppose I could remove the starter and see if it looks like th crank sensor is leaking.

 

[electro]

Did the bulged seal look wet?

I would try and inspect further. Looking for seals that have oil stain along them. Perhaps it could be valley cover seal. Or back or heads??

 

[treehan77]

Did not appear wet, but the main was bulged at he top. Technician said he hadn't really seen that before, and thought it to be slinging oil out that top bulge. How do I inspect the "valley cover seal"? Or the others you suggest

 

[electro]

It's awkward but I would first get under truck with a good light and look way up as far as you can and see just how far up oil is visible. Perhaps an inspection mirror would help.