Anything that generates heat and/or friction will eventually burn or wear out (for example, a timing chain generates heat from friction, subsequently softening the metal chain allowing it to stretch under torque; therefore its life span is limited). With this in mind, a running engine generates tremendous amounts of both; friction is encountered by the moving and rotating parts inside the engine and heat is created by friction and combustion of the fuel. However, the engine has systems designed to help reduce the effects of heat and friction and provide added longevity. The oiling system reduces the amount of friction between reciprocating parts inside the engine. The cooling system reduces heat created by friction and combustion around the cylinder heads and block. If either system is not maintained, a break-down will be inevitable. Therefore, you can see how regular maintenance can affect the service life of your vehicle. If you do not drain, flush and refill your cooling system at the proper intervals, deposits will begin to accumulate in the cooling system, reducing the amount of heat it can transfer from the coolant. The same applies to your oil and filter; if it is not changed often enough it becomes laden with contaminates and is unable to properly lubricate the engine. This increases friction and wear.
There are a number of methods for evaluating the condition of your engine. A compression test can reveal the condition of your pistons, piston rings, cylinder bores, head gasket(s), valves and valve seats. An oil pressure test can warn you of possible engine bearing, or oil pump failures. Excessive oil consumption, evidence of oil in the engine air intake area and/or bluish smoke coming from the tailpipe may indicate worn piston rings, worn valve guides and/or valve seals. In general, it is acceptable for an engine to use one quart of oil every 1000 miles. Engines that use one quart of oil or more in less than 1000 miles should be checked for oil leaks first. Repair any oil leaks before determining how much oil is consumed by the engine, especially if blue smoke is not visible at the tailpipe.