MLS

An MLS head gasket is a composite seal for the cylinder head. It consists of multiple thin steel layers, typically three to five, bonded together with elastomer coatings. The steel layers provide structural rigidity and heat resistance, while the facing materials compress against the cylinder block and head to create a gas-tight seal. This design lets MLS gaskets handle higher combustion pressures than traditional fiber gaskets, making them essential in modern turbocharged and direct-injection engines.

The steel laminations are usually 0.3 to 0.5 millimeters thick, chosen for their spring properties. When bolted down, the gasket compresses slightly but remains stiff enough to maintain sealing force even after thousands of heat cycles. The elastomer facings, often nitrile rubber or synthetic fluorocarbon, prevent direct metal-to-metal contact and allow the gasket to conform to minor surface irregularities. Without these facing materials, the gasket would simply slide off the mounting surfaces.

Why steel laminations matter

Older asbestos-fiber gaskets could swell when hot, losing clamping force as engine temperatures climbed. MLS gaskets remain dimensionally stable across the 20 to 100 degree Celsius temperature range typical of cylinder head operation. They also resist coolant and oil seepage better than fiber, especially in engines with ethylene glycol-based coolants. These advantages made MLS gaskets standard in European and Japanese production by the early 1990s.

Installation requires clean, flat surfaces and proper torque sequencing. Over-tightening can compress the elastomer layers permanently, reducing effective clamp load. Under-tightening allows micromotion that wears through the facing material and causes weeping or blowout. Head surface flatness matters more with MLS than with older gasket types: a warped head will create low spots where the gasket cannot seal reliably. Some workshops now use torque-angle methods rather than pure foot-pound values to control bolt preload more precisely.

MLS gaskets cost more than traditional fiber gaskets but last longer and tolerate higher sustained pressures. They appear in nearly all production automobiles today. Some enthusiasts and rebuilders still stock cork or fiber gaskets for older vehicles, but these are no longer competitive for modern engine duty.