What Happens If Motor Oil Is Not Changed?

Motor oil is essential to the proper running of an engine. Without oil, the engine will seize up. Depending on the damage, the engine may be rebuilt. If the engine cannot be rebuilt due to excessive damage, it must be replaced.

Changing the oil keeps it clean and in optimum working condition. The oil lubricates all the moving parts in the engine. These moving parts have very small tolerances---as small as .0003 inch. A pump moves the oil from the oil pan throughout oil galleys in the engine. If the oil pump breaks, oil cannot be pumped to the pertinent parts, and the engine will seize.

If motor oil is not changed, it gets dirty. If the car has a lot of miles on it, the piston rings may not be as tight as needed, and blow-by gets into the crankcase, which over time dirties the oil. It then makes the oil thicker. Crud in the oil sticks throughout the oil galleys. Once the oil galleys become clogged, the oil cannot drain back down through the engine into the oil pan. The oil builds up in the valve covers, which means there is less oil in the oil pan. Once the galleys are plugged, the bottom of the engine "runs out" of oil (since the oil can't get back down into the bottom). The bearings will seize and the engine will stop running.

Some manufacturers have changed the standard for oil changes from every three months or 3,000 miles to up to 10,000 miles. However, oil should be changed every three to five months or every 3,000 to 5,000 miles, whichever comes first, as all oils can become sludgy at the same rate. When you change the oil at shorter and regular intervals and do the rest of the required maintenance, your vehicle will get better mileage and last much longer.