Scotty,
I am the original owner of a 2008 GMC Sierra 1500 5.3L V8 with Active Fuel Management and 186,000 miles.
A year ago, the truck was running rough and blowing white smoke out of the exhaust. I then discovered that there was a manufacturers bulletin about an issue with the original valve cover that allowed oil to enter the pistons. At 180,000 miles, I replaced the valve cover with the GMC redesigned valve cover with integrated PCV valve. This fixed the problem and the truck ran like new.
Now, a year later and 6,000 additional miles, when I start the truck after it has been sitting overnight, it has a rough idle and it blows white smoke for about a minute. Then the engine warms up and it runs like new. I don't think I'm loosing any coolant.
Before I replace the valve cover again, do you have any other ideas on what is else may be causing this or how I can diagnose the problem? Or, is it time to give up the ghost and get a newer vehicle?
Thanks,
-Todd
First of all, do a block test (see Scotty's video) to determine whether you have a head gasket leak.
Also, you should consider getting wet and dry compression tests done, as well as a cylinder test. It sounds like coolant is leaking into the engine, early stages.
Get the correct diagnosis first, and then decide, based on the facts, what to do with the vehicle.
https://www.youtube.com/watch?v=v0U8Iyf0kk4
