SteveOwens
Active LVC Member
Well the 04 had between 225k when i had to change them. You know when they need attention is when the spark plug hole fill of oil and 90 deg turns cause leaks over the exh manifolds. Mind you that was a one time replacement due to a light Ultra-blue silcone light film on all polished valve cover surfaces. I found above three digits i would smell exh fumes breifly and would go away when not in power drive mode. A sealing issue at hand. When disassemblying the oe engine i observed two exh face indentations behind the last rear manifold stud after a clean polishing. The manifold was indeed causing this but why. My theory was the non-uniform heat expansion of the exhaust pipes and engine mass cocking the manifolds from the cyl head surface. To remedy this, the use of short flex joints on both pipes after the cats have mostly solved this leak. But to a more positive seal RemFlex graphite sheet worked nicely. The other observation when disassemblying the exh maniflod was the oval raised sealing port grooves were nearly flat compared to new units.They were done sealing. One other thing, the clam shells were insulated with ceramic and fiberglass greatly reducing heat within the engine comparement to only heat exchangers. The manifolds were Hot-Jet coated for exhaust flow improvement.
