During engine operation, the pistons are rapidly moving up and down. Engine oil is also moving up and down with the pistons. Not only does engine oil lubricate, cool, and clean; it also seals between vital components. Engine oil seals between pistons and the cylinder walls to reduce blow-by. Blow-by is the gas that escapes past the piston rings and into the crankcase, causing power loss and piston wear. Engine oil acts as a seal between components that are separated by gaskets. For example, you should put a thin film of oil on the oil filter gasket before installation to seal the connection between the filter and engine.