Quote:
Originally Posted by xj_man_646
For whatever reason, the 6.0L in the gmt800 2500/3500s seems to be the application with most common manifold issue. My '04 had the issue, but my '05 1500 with the all aluminum 5.3 does not even after almost 290k miles. I honestly have no idea why this trend exists...
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At a guess, it's an issue of differing materials with differing coefficients of thermal expansions. Aluminum expands and contracts at different rates than cast iron, which expands and contracts at different rates than high strength steel bolts/studs. Add in some galvanic corrosion and extreme heat cycles and you've got a lot of stress. Maybe even stress corrosion playing a role. Or maybe they just spec'd out the wrong kind of fastener. Something too strong may be too brittle to survive the heat cycles and varying CTEs over time. Something too soft that easily survives the varying CTEs may not have enough ultimate strength to survive.