Definition:
All engines use a small amount of oil over time. It gets past the piston rings and valve guide seals and is burned in the combustion chamber. A small amount escapes through the PCV system and a few drops usually managed to seep through a gasket or seal. The question is at what point should one consider oil consumption to be a problem? Any engine that consumes less than a quart of oil every 3000 miles is in excellent mechanical condition. If it uses less than a quart in 1500 miles, it's still in pretty good condition. But once oil consumption exceeds a quart every 1000 miles, it signals the engine is approaching retirement. Blue smoke in the exhaust or oil consumption on the order of a quart or more every 500 miles indicates serious oil burning problems (usually due to worn or broken piston rings, a cracked piston, or worn valve guides and/or seals). Sometimes a leaky seal or gasket can make an otherwise good engine use oil. The most frequent leak points are valve cover gaskets, crankshaft end seals and oil pan gaskets. Tightening the valve cover or pan bolts can sometimes stop a leak but usually the only cure is to replace the gasket (See Gasket).
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