Originally Posted By: Scorch
Why would this happen?
I've heard several hypotheses:
1) Aluminum timing cover on an iron block. Differentials of thermal expansion tears the gasket over time.
2) Corrosion of the timing cover around the pump inlet/outlet which pits the cover and causes the gasket to fail. (I've seen the pitting every time I've changed one.)
3) Heat from the cat as mentioned above.
Seems that when the water pump is replaced, the torque applied to the timing cover during removal and installation can disturb the already weakened seal and a few more heat cycles leads to a leak.
Just something to live with if you own a Vulcan. Religious maintenance to the cooling system may forestall the problem, but if you keep the car long enough it seems destined to happen. At least the coolant generally leaks externally and not into the crankcase like the 3.8's.