Head gasket(s) + rear main seal jobs

[bushraticus]

I bought my dad's 2007 Yukon Denali 6.2 with approx. 150K miles out of his estate about six months ago and need some advice on a couple of things. The problems started a few months after that when a coolant hose blew when I was on a dark trucking highway with kids in the car and nowhere safe to pull over. I had to drive it a few more minutes than I'd have liked, maybe 3 or 4 minutes with the dash freaking out more and more. The engine definitely got overheated, how badly I don't know.

I had that hose replaced by mechanics who said everything seemed fine though I noticed a slight continued burning smell that they couldn't explain. They did however notice the rear main seal has a slow leak when I asked them take another look. Fast forward to a few weeks ago when the tire guys noticed a pretty big pool of slightly oily orange fluid while installing new tires (maybe a cup or two?). Took it back to the mechanics who said fluid levels were good and all seemed well. Then I noticed the leak again a few days later on the deck of a ferry I was taking, which gave me a chance to mop up and save some which I took back to the mechanics after my vacation.

This time they found coolant leaking down the back of the head down into the area where the rear main seal is leaking oil. My guess is that some of the coolant is getting cooked after it leaks out (the unexplained smell) and the rest picks up a little surface oil on the way to the ground.

The next step is for me to take it to another shop that can tackle bigger jobs than these guys but I thought I should ask here a) what people thought of my theory and b) how much labor is shared between the head gasket + rear main seal replacement jobs? The head gasket seems the more pressing of the two but maybe they should be done at the same time if there's lots of labor overlap.

 

[Blackcar]

You might check the T on heater hose at firewall.

 

[bushraticus]

You might check the T on heater hose at firewall.

Will do, thanks!

 

[wjburken]

b) how much labor is shared between the head gasket + rear main seal replacement jobs?

Not much shared labor between those two repairs unless you plan on pulling the motor to do the heads, which isn’t necessary. Heads are up top and don’t get you near the rear main seal. You need to pull the transmission to get to the rear main seal.

 

[petethepug]

Also check the coolant reservoir for cracks. It’s make of a plastic that allows fluid out ONLY at operating temps.

Run the truck, warm it up and let it idle with the hood open & a/c running. It WILL reveal itself.

 

[Airman68]

As far as the rear main, I've had a number of these and a pool of oil is usually not that. Sometimes oil leaks are hard to find. The truck I have now, the oil leak was a $5 gasket on the oil cooler block off cover. Sometimes it's a valve cover gasket that drips down the back of the engine. I've trained myself to look for the simple things first and you'll be right 90% of the time.

 

[tom3]

I suspect the head (s) might have been warped just a bit from the overheat which would have been pretty severe for that part of the engine. Could be the heads will need some machine work if not actual replacement. GM does have a cooling system sealer that was designed for this leakage and was used in factory fills in the early aluminum headed Cadillacs. Good sealer and causes no other problems.

 

[Geotrash]

I suspect the head (s) might have been warped just a bit from the overheat which would have been pretty severe for that part of the engine. Could be the heads will need some machine work if not actual replacement. GM does have a cooling system sealer that was designed for this leakage and was used in factory fills in the early aluminum headed Cadillacs. Good sealer and causes no other problems.

On that engine, the block is aluminum as well, so it could be either or both if there was a metal problem. But I would wager that even driving it for a few miles without coolant wouldn't be enough to kill it. An aluminum head on an iron block would warp the heads due to the difference in thermal expansion rates. But on an all aluminum engine, the leak may be something else like the aforementioned coolant tees on the firewall. I'll bet one of them let loose causing his original problem and the other is now leaking.

Air-cooled aluminum aircraft engines run around at 400F for CHTs all day long, and above 450ºF is generally where metallurgical changes *start* happening for aluminum engine alloys, so these engines can likely tolerate a pretty decent overheat event without being ruined.

 

[mattbta]

Rent a cooling system pressure tester and see if you can spot external leaks. You can also buy some General Motors 89022219 ACDelco 10-5046 Dex-Cool Leak Detection Tracer Dye and get a UV flashlight/glasses to help if it isn't obvious.

 

[donjetman]

Did my rear main in 2018 when it had 130k miles and today its still dry as a bone with 190k miles. Here ya go with a lot of pics:
https://www.tahoeyukonforum.com/threads/rear-main-seal-job-pan-etc-07-yukon-denali-6-2.108334/