If the head gasket on an ATV blows, meaning a tear forms in the seal, the engine will loose radiator fluid and be unable to maintain proper operating temperatures. The result is engine overheating and then engine seizure. Unlike replacing a blown head gasket in an automobile, replacing one on an ATV is not as difficult or as expensive but it is still important that you replace the gasket to prevent further engine failure and additional repair costs.
If a head gasket is blown on a liquid-cooled ATV engine, it can leak antifreeze into the combustion chamber. Once ignited, it leaves the exhaust pipe in the form of white smoke. This looks similar to when you first start your ATV in cold weather, except it does not go away after the engine warms up.
When a head gasket blows on a liquid cooled engine, antifreeze leaks out from between the mating surfaces of the cylinder head and the engine block precisely where the gasket has blown. If the fluid does not flow into the combustion chamber, it runs down the cylinder and onto the crankcase. A visual inspection of the cylinder and crankcase can tell you if the head gasket has blown.
In rare instances, the ATV will mysteriously loose antifreeze but it will not show up in the form of smoke or leaking. Generally, you will notice this when checking the radiator fluid level. This typically means that the antifreeze is leaking into the oil pan. Drain the oil from the oil pan and inspect it for antifreeze. The antifreeze will separate from the oil and be noticeable.
When the head gasket blows on an air-cooled engine, oil could leak into the combustion chamber and when it ignites, the engine will produce black smoke. The amount of black smoke increases as the engine accelerates. If the oil does not leak into the combustion chamber, you will likely see oil on the cylinder and crankcase as it leaks from the head. Black smoke could also mean the piston rings are worn out. If oil is not present on the crank case, perform a compression test to determine if the oil consumption is due to a leaking head gasket or worn piston rings.