TIP In combination with the cylinder-head gasket’s quality, it is the surface finish of cylinder head and engine block as well as the gasket’s installation that are decisive for good sealing results. Component unevennesses and distortions, reused head bolts, and the use of grease, oil or liquid sealing compounds will deteriorate the sealing effect of even the best MLS cylinderhead gasket. Therefore, the manufacturer’s installation instructions must be strictly observed.
Typical three-layer MLS cylinder-head gasket with top sheet, active layer with Wave-Stopper® technology, and bottom sheet. Beads plus full-surface elastomer coatings improve the sealing potential of these modern sealing systems. Beads for macro sealing, and elastomer coating for micro sealing.
Typical leaks between cylinder head, cylinder-head gasket, and engine block involve gas, oil, or coolant leakages. These leakages occur between combustion chambers, into the coolant circuit, or to the environment. Gas leaks can result in fatal engine damage within a very short time and oil leaks can cause severe environmental pollution.
Pressed-in dirt or foreign objects as well as rough surfaces also cause damage to cylinder-head gaskets. Component unevenness leads to gas blowby between the combustion chambers, and consequently to gasket failure.
Therefore, thorough cleaning of the sealing surfaces is essential before installing the cylinder-head gasket.
Typical media leakages with MLS cylinder-head gaskets.
TIP In professional terminology, leaks between cylinder head, cylinder-head gasket, and engine block all fall under the general term ”leakage”. This always involves an uncontrolled exit of media (gas, oil, coolant) between cylinder head, engine block, and cylinderhead gasket.
Damage Analysis of MLS Cylinder-head Gaskets Damage to multi-layer steel cylinder-head gaskets mostly involves two sealing elements: beads and elastomer coatings.
Bead Fractures due to excessively high Component Dynamics Possible causes for excessively high component dynamics are faulty, reused, or unlubricated cylinder-head bolts; incorrect bolt torquing due to excessively high friction during installation; and damage to cylinder head or engine block. Component distortions can also be the result of engine overheating. Similarly, if an engine is operated under pinging conditions (pre-ignition), the high temperatures and pressures can lead to higher component dynamics and possible bead fractures.
Detached Elastomer Coating due to Overheating Classical causes for overheating are defects of the water pump, radiator, thermostat or hoses, but also insufficient coolant or incorrect venting of the coolant system can lead to thermal problems. Failure of the catalytic converter can also result in higher temperatures due to increased exhaust back pressure.
TIP FROM THE EXPERTS If the elastomer coating of a removed defective cylinder-head gasket can be peeled off the metal substrate easily with a fingernail, engine overheating is the most likely cause of the failure.
Broken web caused by high component dynamics
Elastomer coating damaged by overheating
Elastomer Coating destroyed by Antifreeze Agents Contact with antifreeze agents that have not been approved can cause the elastomer coating to become detached from the metal surface. Subsequently, the dislodged elastomer particles can clog the coolant channels and interrupt the coolant flow. The result is an overheated engine. Other typical damage profiles for MLS cylinder-head gaskets are destroyed combustion chamber seals due to incorrect cylinder liner protrusion or faulty liner flange seats, as well as severely damaged Ricardo squish areas due to detached swirl chambers.
TIP FROM THE EXPERTSP Cylinder-head bolts tightened using the torque-angle method are elongated permanently. After disassembly, they are clearly longer than new bolts. If reused, they can break. Therefore, new cylinderhead bolts should always be used when replacing a cylinder-head gasket.
Causes for blowby are excessively high combustion pressures, rough sealing surfaces, component distortions, or inadequate compression of the cylinder-head gasket.