Coeficient of linerar expansion.

[Canuck]

Not since my Grade 11 Physics class have I needed to relate to the effect on dis similar metals.
My mechanic told me I had two broken bolts on the exhaust manifold of my 2003 Yukon XL 2500. It has the 6 litre Vortec with Aluminum heads. The two end bolts were broken off and had not been tampered ith from new. So Why? Seems the rate of thermal expansion between the aluminum head and the cast manifold causes stress on the bolt heads and with normal metal fatigue they snap. If ignored the cast manifold will warp with enough heat cycles if not torqued properly. New gasket and all new bolts required. Must be a common problem as The local GM warehouse had 23 Manifolds in stock. Mine was not warped enough to warrant replacement.

DO A VISUAL ON YOUR MANIFOLD BOLTS NEXT TIME YOU ARE CHECKING OIL!