For anyone who might be interested:

I've posted previously about a smoking issue; at 90k miles my 08 yukon hybrid would smoke on a cold (sit for 4-6 hours in Minnesota winter) start, but intermittently. The first solution by the dealer (Ryan Chev in Buffalo, MN; not sure if I'm allowed to say that but they've been incredibly good to me! You'll see why in a bit.) was to replace the head gaskets.

Head gaskets done, the problem *seemed* to go away, but it was always intermittent so that may well have been coincidence. Then, around 103k it started smoking a lot more consistently and clattering on cold starts as well. I've done the research about lifter problems with the AFM (v4/v8) engines, and I've actually had the issue of oil pressure dropping out due to a clogged secondary oil filter under the oil pressure sender. I'm sure that was the primary culprit to the issues that cropped up, though I'm still a bit baffled by the smoking.

In the end, the smoking was due to worn valve stem seals, and the clattering was a lifter or 4 or 8 or who knows how many that was going flat over a sit and taking its good sweet time regaining pressure. The dealer agreed to split the bill with me (I probably paid 15% of it) given that I'd been in to fix the problem before my warranty was up. (And a free loaner while it was out; very happy with them!)

What did they do?
All new lifters. All new valve stem seals. Pressure test the heads, some valves were not sealing completely so all valves were re-ground and seated. Replaced the small oil filter under the oil pressure sender; it was easily accessible so may as well. All new plugs; OEM at 100k+ miles, and the heads are off, so why in the world not do plugs? And all the gaskets/bolts etc that goes with this work. Finally, full synthetic oil, which has been used since the oil pressure incident and will be used hereafter.

Sad that a modern vehicle with only 100k miles would need this sort of service, but extremely impressed that the dealer didn't just say screw you because it wasn't "broke" to the point of not working at all. Too many out there wouldn't touch anything like that because it's not 'bad enough' to bother. I don't want to pay another tow, so I'm happy they took care of things.

All in all, I've been very happy with this truck, and intend on keeping it till the next generation of hybrid full size SUV comes out; seems I could be driving this thing awhile at the rate GM is working.

My only caveats: The service work (I'll chalk it up to teething issues), the ridiculous door lock modules, NO SPARE TIRE!!! (I'd like to slap somebody for that one!) and the week it takes to shift modes. I'm an EE student, and wish beyond anything to pick the brain of one of the design engineers that worked on this powertrain. There has to be a way to tell it that if the driver has their foot to the floor, they want it to GO! regardless of how smooth it is. This thing could be really quick on its feet if it didn't take all day changing 'gears'. Oh, and a tow/haul mode that would force it to use the static gears in the transmission along with allowing the engine to lug a bit would be nice too; cruise control has this thing wide open up the tiniest of grades when my foot can keep the RPMs under control.

Ok, I'm done now. Just wish I could have more control over what it does and when it does it. Then again, I don't know that I'd want to learn all 10 million lines of computer code that are likely to be stored in this beast.

 

It is really good to hear that you and your servicing dealership have all the engine issues all worked out now.

Thanks for the update.

 

I had a problem with my engine...check engine light came on, code was for cylinder 4 misfire. I had a buddy take a look at it. He check spark plugs, all were gunked up with black buildup. Only 40k miles on it. He said tha wasn't good. I changed all with new delco iridium tips and still had same code, so we swapped coil packs... Same issue, so I brought it to the dealer. Prognosis was lifter on cylinder 4 got stuck and causes the lobe on the cam shaft to wear down. They replaced all lifters, camshaft, seals, and head, all under warranty. When I got the truck back it ran like new. I actually forgot how good it ran. Before the "surgery" I was getting between 17-19 mpg's. after i am getting 23-25mpgs hwy per tank using premium non-ethanol fuel. And I'm not exaggerating. I now have 46000 miles on it and still running good.

2008 Tahoe hybrid 4X2