[swedishsteel]

Depends how you drive it--long enough trips so the engine gets up to operating temp and stays there for a good period of time, you can go quite aways between changes. On the other hand, if you just go a couple miles and back most of the time, the engine doesn't get hot enough to evaporate the moisture, which causes sludge and acid, etc. then you need to change quite often, especially if you don't have a filter.