tl;dr Which is best? Buying high-quality, longer-lasting, but more expensive oils and changing oil less frequently or buying lower-quality oil but changing more frequently?
As I'm trying to find my way in engine oil land, I am basically stuck at the following dilemma. I own a BMW E46 from 2001, so in my example, all of the oils I'm talking about are fully synthetic and at least BMW-Longlife 01 approved. There are high-quality, but expensive oils that claim that they last longer than conventional oils (and this claim is BMW approved). With a little bit of simplification (not taking into account the negligible price of an oil filter and rounding prices a little), I can choose to:
- either buy the more expensive oil and do oil changes only every 10,000 miles/15,000 kilometres;
- or buy the cheaper oil (1/2 the price of the more expensive oil) and do oil changes every 7,500 kilometres.
As you can see, the overall cost would, more or less, remain the same, so I'm wondering which option would be best. Since price doesn't make a difference, and I don't mind doing oil changes more often (it's only 15 min. of work, after all), so what is the best option to prolong engine life?
EDIT: I was mostly interested in the general case, but in case any of you really know a lot about specific oils, these are the two oils I was talking about: