The head gaskets on the 6.6L LLY Duramax (2004.5–2006) seal the cylinder heads to the engine block. They keep combustion pressure, coolant, and oil in place. These multi-layer steel (MLS) gaskets handle high compression and boost.

They’re stronger than the LB7 versions but can still fail—especially in tuned or overheated engines. Signs of failure include coolant loss, white smoke, or bubbles in the overflow tank. Upgraded gaskets and ARP head studs are a common fix.

A solid head gasket job keeps compression strong, stops leaks, and supports more power in any LLY build.