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In 1991, Ford introduced the 4.6L OHC V-8, commonly referred to as the Modular Ford V-8. It had, for its time, a revolutionary new head gasket design called MLS. Prior to that, most head gaskets were steel core designs with some sort of gasket paper attached to the core, so this was a big change for the engine repair/rebuilding industry.

MLS actually stands for Multi Layered Steel and describes the construction of the gasket. MLS gaskets usually have at least three layers. The inner layer, sometimes referred to as a passive layer, serves three general purposes. It provides a means of getting the proper thickness for the gasket, provides a layer for the top and bottom layers to push against and in some designs, provides extra thickness around the cylinder to ensure good combustion seal.

The outer layers, referred to as active layers, are tempered stainless steel. They have raised beads, called embossments, surrounding the critical sealing areas. This would be, of course, the combustion opening, the water jacket openings and in the case of OHC engines, the oil passage from the block to the head.

When you install the head on the engine and start to tighten all of the fasteners, aka head bolts, the spring steel beads of the active layers resist flattening out and push back against the passive layer on one side and the head or block on the other. It is this spring pressure that creates the seal and also gives the ability for the gasket to keep sealing as the engine runs; you may not know, but the heads actually lift off the block.

Combustion pressures can range from 1,800-2,000 psi. Just cruising down the highway, these forces are happening at 1,000 times a minute the entire time you are driving, racking up millions of cycles over the life of the engine.

Now if our engine had no coolant and no oil that needed to pass through the head gasket, we could stop our conversation right now. But since that’s not the case, there is another enhancement to MLS head gaskets that is absolutely required to make them work. That would be “rubber” coatings.

Now calling these coatings “rubber” is kind of like calling LeBron James a “basketball player.” Neither term gives justice to what we’re talking about. The rubber is actually carefully compounded and tested. There is also a skillfully applied polymer coating added to the rubber. It gives the gasket the ability to seal fluids perfectly through the millions of cycles mentioned above!

Victor Reinz has been in the MLS gasket manufacturing game since the days of the first Ford in 1991. Millions of MLS head gaskets have been made both for OEM customers and to supply the aftermarket needs of customers.

Looking at other competing brands of MLS, you can’t judge good MLS by its appearance. Some cheap imitators cut corners two ways: they select a stainless steel that’s cheaper but not tempered correctly and they select a lower cost “rubber” coating material. The end result is early failures. Because of the long and extensive involvement of Victor Reinz with OEMs, they don’t cut corners on materials.

In part two of this story, we’ll look at gasket installation, surface finish requirements and head bolts, or as we call them today; fasteners. You’ll learn about tightening these fasteners and why many manufacturers recommend they be replaced each time the head is removed.”4.6l

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Engine Builder Staff

Engine Builder Staff