I have a Chevrolet 2008 suburban 1500 v8 5.3L, and am looking for a problem that dirties the spark plugs and causes stumbling idle especially when cold. I am suspecting the valve guides are worn, causing an oil burn (it has been oil thirsty for a long time). All cylinders passed a compression test. How can I tell if the valve guides are worn? Would the compression test have revealed that?
If you have a problem with oil getting down the valve guides, it usually isn't the valve guides which are the problem, but the valve stem seals at the top of the cylinder head underneath the valve springs. If the seals are worn out, it allows oil to get past and due to the action of the valves themselves and the force of gravity, it pretty much acts like a pump pushing oil down. In order to tell if this is the issue, you pretty much have to pull the head apart and check the valve stem seals manually.