Originally Posted by WickedJstr
What are some signs of the uim failing. I'm not leaking any Coolant or anything i have noticed that when ireplaced my Alternator that there was a lot of grease and crap underneath the Alternator near the Intake manifold tho i dont know i might just replace it for the fact of just doing it. It'* got a 109k on the odo so i'm sure it woudn't hurt.
First indication of UIM failure is usually loss of coolant at a greater rate than evaporation, which is very slow. If the leak is to the outside, coolant running down over the transaxle. Otherwise, no external leaks or drops underheath the car, but coolant level continuously dropping indicating an internal leak. This does not for sure indicate a bad upper; it may be a failure of the lower intake gaskets to the cylinder head, or in very rare cases, a bad head gasket. Internal failure of the upper can result in coolant drawn into the combustion chamber whcih you may be able to see by examining your plugs. If it is a trickle into one cylinder, that plug will appear cleaner than the rest. Coolant through the combustion chamber will destroy your oxygen sensor, too.
The uppers can fail catastrophically too. One minute everything is fine, the next, tons of white smoke as coolant pours into the combustion chambers.
A cooling system pressure test will reveal if you have an internal leak.
When removed, the upper plastic manifold typically looks OK around the stovepipe until you start to test its integrity with a sharp pick. The heat carbonizes the plastic leaving a soft, porous residue that appears to be solid plastic, but is really rotten.