Multi-layer steel (MLS) gaskets seal the engine block to the cylinder head using three to five thin steel plates coated with a synthetic rubber like Viton. The outer layers feature embossed ridges that crush flat when torqued down, creating a tight seal around the combustion chambers and coolant passages. They are the standard replacement for older composite gaskets because they handle higher compression ratios and thermal expansion without blowing out.
I ordered an MLS gasket for the rebuild so we don't have to worry about blowing it under boost.
When installing an MLS gasket, the block and head mating surfaces must be machined exceptionally smooth; any roughness that a composite gasket would forgive will cause an MLS gasket to leak.
Related terms
Head gasket
The critical seal positioned between the engine block and the cylinder head.
Cylinder head
This cast metal component bolts to the top of the engine block to seal the combustion chambers.
Compression ratio
The mathematical ratio of cylinder volume at the bottom of the piston stroke compared to the top.