ENGINE OIL:   Engine oil is very important to the life span of an engine.   Dirty oil will cause premature wear to the moving parts of the engine.   The illustration above is an engine oil filter that rusted to the point it developed an oil leak.   For and oil filter to rust to this degree it had to have been on the vehicle way to long.   Oil change recommendations very from 3,000 ~ 7,000 miles depending on the source of the recommendation. My advice to anyone interested in keeping an engine in top mechanical condition is to change the oil more frequently.   The additional engine wear caused by dirty oil will shorten the life span of the engine and cause oil consumption and performance loss.