2002 Yukon XL Oil Leak

rvhoehn · September 7, 2014

HI, I'm new here and have an oil leak on my 2002 GMC Yukon XL, 5.3L, 90,000 miles. The oil is leaking from a small rectangular (THING?) located above the rear axle on the drivers side. The THING? is about the size of a cigarette pack and has a couple of rubber lines goi9ng to it. Can anyone tell me what the THING? is, what it does and why it might be leaking oil? Maybe even what can be done to stop the leak?

Thanks

Randy

bamcis · September 8, 2014

I don't believe it is oil. Sounds like it's brake fluid leaking from the brake line splitter. But who am I? I will yield to the more wise ones here.

rvhoehn · September 9, 2014

Hi all and thanks for checking in. I have added some pics of the THING?. Let me know if you know.

Thanks

Randy

txab · September 9, 2014

Looks like the evap soleniod. Have you checked what the fluid is? That should be fuel if it's the evap sol.

rvhoehn · September 9, 2014

It is oil. Drips to the floor and doesn't evaporate.

txab · September 9, 2014

All I can tell you is that is the vapor canister vent solenoid and there should be no oil at that location. It's part of the emission system and basically provides venting the tank. Fuel can pushed into it if you overfill the tank

rvhoehn · September 10, 2014

I don't see any oil on the pinion or yoke that would indicate oil was being slung outward and it is only wet around the solenoid. Is the vapor circuit connected to the crankcase? Could it be blow by?

txab · September 10, 2014

It's connected to the intake by vapor canister purge valve, also there is a charcoal canister in the evap system as well

rvhoehn · September 10, 2014

Thanks, I'll see if I can pull the tube off at the solenoid and look inside for oil. If its dry I gotta find the source somewhere else. Any hints/thoughts where I might find a diagram of the evap system to help me find what I am looking for/where to do some checks at the engine?

txab · September 10, 2014

This explains how the system works.

http://www.gm-trucks.com/forums/topic/104569-the-evap-system/

bamcis · September 10, 2014

All I can tell you is that is the vapor canister vent solenoid and there should be no oil at that location. It's part of the emission system and basically provides venting the tank. Fuel can pushed into it if you overfill the tank

Above the rear axel? Seems like a strange location to put that, even for GM.

rvhoehn, by any chance can you post a pic or two showing the canister a little further away? You know, something to give some context.

I admit I'm not the sharpest knife in the drawer and perhaps txab is right, but with it leaking oil, now I'm wondering if it has something to do with venting the rear axel. Or perhaps it locks the rear axel?

txab · September 10, 2014

You must remember the fuel tank is that area, and the vent solenoid is nearby

rvhoehn · September 27, 2014

OK and thanks for the input. I finally got the thing up on jack stands in good light. I do believe I was mistaken of the source. I now believe the oil is coming through the yoke and leaking from behind the pinion nut. The dirt seal around the pinion is dry, the outside on the yoke is dry, and however the inside of the yoke and the pinion nut are wet with oil and I do see evidence of oil having been on the exhaust.

What is my next move? Mark the pinion nut, remove it and the washer, clean and apply sealant to the back of washer and return pinion nut back to markings?