Hot spots tend to form in areas where exhaust ports are located next toĮach other. Sealing the engine, and it can withstand high temperatures and draw heatĪway from hot spots to reduce thermal stress and loading. Relatively soft material that provides good conformability for cold Graphite has natural lubricity that can handle the differences inĮxpansion between aluminum heads and cast iron blocks. On many late model engines, graphite head gaskets are used because Seal when it is first installed, and helps it maintain that seal by This improves the gasket's ability to form a good cold Raised silicone, Viton or fluoroelastomer sealing beads are oftenĪpplied to the face of the gasket to increase the clamping pressure inĬritical areas. Movement and scrubbing at the gasket surface. On these applications, the rate of thermalĮxpansion for the head and block is the same so there is much less This is the opposite approach to what is done with many head gasketsįor cast iron engines. This allows the head to expand and contract without ripping the gasket Low friction coatings prevent gaskets from sticking to either surface. Gasket manufacturers deal with the scrubbing problem in bimetal engines is
This compares to 60 to 120 RA for cast iron enginesĮqually important is the design of the head gasket itself. That is why surface finish is so important on today'sįor bimetal engines with composition gaskets, the recommended surfaceįinish is 20 to 50 RA. If the surface finish on a bimetal engine head and block is too roughĪnd digs into the gasket too deeply, it can literally tear the gasketĪpart over time. Of these applications that solved the original problem. Fortunately, the aftermarket developed replacement gaskets for all Rate of premature failure because the OEM head gasket could not keep a All of these engines have experienced a high Going further back, we all remember the problems GM had with theĢ.3L Quad Four head gaskets. If the head gasket cannot handle this motion and is not strong enough to withstand the shearing forces that occur every time the engine is started, run and allowed to cool back down, itĮxamples bimetal stress causing a head gasket failure include the OEM head gaskets in the Dodge Neon 2.2L, Ford 3.8L V6 and Toyota 3.0L and 3.4L V6Įngines. The difference in expansion rates creates a lot of motion and Heads save weight but expand 1.7 times faster than cast iron when they get hot. Today is the use of aluminum cylinder heads on cast iron blocks.
The most common cause of head gasket failure is usually overheating, often as a result of a coolant leak, a bad thermostat or cooling fan failure. When a head gasket fails, there is usually a reason why. Maintain that seal for the life of the engine, which might well beġ50,000 miles or more on many of today's engines. Provide a leak-free seal from the moment it is first installed, and The head gasket seals the engine's combustion chambers as well as theĬoolant and oil passages between the head and block. Head Gasket Failure by Larry Carley copyright 2019
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