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!

[mockingbird812]

Warranty work or recall (I know what the answer to that is <<GRAEMLIN_URL>>/rolleyes.gif)? Unacceptable engineering in any case!!!!!!!!!!!

[William]

The 6 cylinder engine used in the 2003-up Trailblazer also has that problem. I found a broken off bolt head in the garage one day. Since you can't see the manifold it is not that obvious. Lerned later what the problem was. Good thing we had extended the warranty. They replaced all bolts and the manifold; 7 hours labor. It can be worse-if the bolts snap off flush with the head the engine has to be removed to repair it.

[Canuck]

The bolts broke at the top so they could be removed once the manifold was off. My mechanic warned me if things got ugly then the head might have to be removed then the story would have escalated:
While the head(s) are off we might as well.....
Since your heads are fresh it make sense to.....
You know a fresh motor in front of a 9 year old tranny....
Do you really want to be driving a truck that color now that everything else is new...
Re upholstering the seats would add to that new truck feeling.....
Wheels and tires from TireRack......

[Plowman]

If the bolts snap off flush with the head the engine has to what...

[jannes_z-28]

I had that problem on an Opel with the 2.0 Ecotec engine. The explanation was that the manifolds bolt hole were a little to tight and when hot expanded and pinched the bolt and pulled it. Eventually the bolt would snap at the head. As mine did, the mechanic were able to repair it without pulling the engine. Small engine, big car = lots of room to work.

GM was aware of the problem and on later models they made the hole in the manifold slightly larger so that the bolt would not stuck in the hole.

Jan

[Plowman]

So GM was aware of the problem later so they fixed it for you under Warranty.

[jannes_z-28]

Warranty had run out when I got my problem.

Jan

[300deluxeL79]

very common (broken ex bolts) on the truck LS engines. probably due to using too small a bolt dia. 8mm/5/16&quot;.
my '03 K1500 5.3 has the rear bolt snapped off on both sides when i bought it. they don't leak.

[Plowman]

The problem is to get the broken bolts out.