How Often Should Oil and Filter be Changed?

Change oil and filter often enough to protect the engine from premature wear and viscosity breakdown. For most most cars and light truck, the standard recommendation is to change oil and filter every three months or 3,000 miles, which ever comes first.

Most late model owner's manuals say that except for "Severe Service" applications, oil change intervals can safely be stretched to once a year or 7,500 miles, with filter changes at every other oil change. When auto makers make such recommendations, one assumes that they are based on extensive durability testing. After all, auto makers themselves would have to bear the warranty cost should their maintenance recommendations prove inadequate.

With proper maintenance, there is no reason an engine shouldn't go 100,000 miles or more with out developing a thirst for oil. That is why most oil companies, as well as aftermarket service professionals recommend changing oil and filters every three months or 3,000 miles.

They also make such recommendations because many motorists are not aware that the should follow the "Severe Service" maintenance schedule in their owner's manual, calling for oil and filter changes intervals of 3 months or 3,000 miles. Severe service (as defined by auto makers themselves) includes:

• Making frequent short trips (less than five miles)

• Making frequent short trips (less than 10 miles) when temperature is below freezing

• Driving in hot weather stop and go traffic

• Extensive idling and or slow speed for long periods of time (taxi, police, door to door, etc)

• Driving at sustained high speeds during hot weather

• Towing a trailer

• Driving in areas with heavy dust (gravel roads, construction zones, etc.)

Protective additives in motor oil do not hold up well in these driving conditions for several reasons. If the engine is not running long enough to get the oil hot, condensation and fuel vapor will not boil off. Contaminants will accumulate in the crankcase, leading to formation of corrosive acids and sludge.

Excessive idling and high operating from towing and high speeds driving during hot weather accelerate viscosity break down. Exposure to dust can put dirt particles in the crankcase. The filter also needs to be changed every time for two reasons. Today's pint-sized filters do not contain as much as much filter material as their quart-sized counterparts. The filter contains dirty oil that can contaminate fresh oil added during an oil change.

Considering what five quarts of oil and a filter cost, verses the course of replacing an engine, it is better to change the oil filter a little more often than might be absolutely necessary rather than risk not changing it often enough.