Air Cooled Engines: Blocked Cooling Fins Blocked rotating screens and plugged cooling fins prevent fresh air from cooling the engine. The result is overheating, which leads to failures of the piston and rings, as well as valves, valve guides and valve seats. Below is a single cylinder engine destroyed by overheating. Grass accumulation on the right side of the cylinder and along the top of the cylinder head, obstructing air flow across the cooling fins: The cylinder was severely scored, and the intake valve seat popped out of the block, lodging under the valve. This engine died young, and needlessly, due to lack of maintenance. Even if maintenance is preformed, sometimes nature can wreak havoc on your engine. The unit shown below was home to a field mouse, which built a nest that blocked cooling fins. Mice also chew electrical wiring, which causes additional expense. Mice are an issue when equipment is used infrequently, and during off-season downtime. Crankcase breathers leaking oil are another cause of overheating. The oil is scattered by the fan, and coats the engine block and cooling fins. This oily film hinders the transfer of heat from the cooling fin surfaces to the passing air. If the oil leak is not repaired, dust particles (which would normally pass through the fins harmlessly) start to accumulate on the oily surfaces. As a result, the cooling passages eventually become completely blocked as well. If oil and sludge are found mixed with debris in the cooling fins during routine maintenance, locate and repair all oil leaks immediately. Back to Kohler-Chantilly Page