I have to disagree with JCL on his time based engine oil change interval, especially considering that he is in Vancouver for one simple reason - condensation. Moisture develops in the crankase from short trips - those times when the oil is not at normal operating temperature for at least 20 to 30 minutes. Even here in Texas, it takes 20 minutes just for those eight quarts of oil to get up to their regular temp of 210-220 degrees. Without having enough time at those temperatures, the oil can't completely "burn-off" the moisture and fuel dilution that it contains. Aside from dirt, those are the contaminents that actually deteriorate the oils lubricating properties.

Even when my wife was only driving her 325i less than 1000 miles per month, I still changed the oil each spring to flush out any moisture that had built up over the winter. Synthetic oil is very tolerant of heat, and usually better at dealing with the effects of moisture. But it's not worth the cost of an oil change to push it past an annual service.

By the way, my automotive engineering degree is from General Motors Institute, and I've had experience with vehicles such as the Cosworth Vega, Pontiac SD455 and Turbo V-8s, Buick Turbo V-6, Buick GSX 400 and 455 Stage I. With ten years in automobile assembly and another ten with Tier One suppliers, I've been around the block.

Don't leave your oil in the engine for more than a year unless it's in storage and not being driven!

2002 X5 3.0
2004 325i