Frequent oil changes will eventually do more harm than good. The engine runs at low pressure for a few seconds or even minutes depending on how good the oil circuit design is. There is also the fact the new oil is thick so has a run-in interval and the number of times the drain plug is designed to be used. Changing your oil every ten miles is bad. At half the recommended service interval probably just wasteful. Between the two, who knows.
The service timing is set the same way as the miles, by a sales team. The engine has a breather so oil many years old will be contaminated with water so may need changing. Ten year old oil might be fine in Saudi, in Southampton it'll be brown sludge. Two year old I think is commercial thinking.
There are some very clever laboratories that can tell you if your oil is wearing out or contaminated. They give huge variations in results. Trucks used in copper mines for example need serious, mechanically cleaning air filters but as they never stop the oil lasts forever until the breather filter goes. Transmission fluid on Hong Kong busses was changed at 1/10th of the UK interval at one point (wet and polluted air plus stop-go running). The analysis charge is well worth it when you are running 300 double deckers or 100 tonne tippers that use hundreds of gallons of oil. The only analysis I've seen on a Wee said 5000 plus miles was just fine. This was an American chap doing a pretty normal series of rides if memory serves.
Andy
