Most late model owner's manuals say that except for "Severe Service" applications, oil change interval can be safely stretched to once a year or every 7,500 miles, with filter changes at every other oil change.
When auto makers make such recommendations, one assumes they are based on extensive durability testing. After all, auto makers themselves would have to bear the warranty costs should their maintenance recommendations prove inadequate.
Except for Chrysler's 7/70 powertrain warranty, and a few others that go up to 5/50 or 6/60, most new car powertrain warranties don't go beyond 3/36. So where's the risk? There isn't any.
With proper maintenance, there is no reason an engine shouldn't go 100,000 miles or more without developing a thirst for oil. That is why most oil companies, as well as aftermarket service professionals, recommend changing oil and filter every six months or 3,000 miles.
They also make such recommendations because many motorists are not aware that they should follow the "Severe Service" maintenance schedule in their owner's manual, calling for oil and filter change intervals of three to six 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 temperatures are below freezing
- Driving in hot weather stop-and-go traffic
- Driving at sustained high speeds during hot weather
- Towing a trailer
- Driving in areas with heavy dust (gravel roads, construction zones, etc.)
- Extensive idling and/or low speed driving for long periods of time (taxi, police, door-to-door delivery, etc.)
Protective additives in a motor oil do not hold up as well under such driving conditions for several reasons. If the engine is not running long enough to get the oil hot, condensation and fuel vapors will not boil off. Contaminants will accumulate in the crankcase, leading to formation of corrosive acids and sludge.
Excessive idling and high operating temperatures from towing and high speed driving during hot weather accelerate viscosity breakdown. 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 filter material as their quart-sized counterparts. The filter contains dirty oil that can contaminate fresh oil added during an oil change.
Considering what four quarts of oil and a filter cost, versus the cost of replacing an engine, it is better to change oil and filter a little more often than might be absolutely necessary rather than risk not changing it often enough.