When should I change my oil?

QCan you settle a pub debate? My Jaguar XJ-S covers about 3000 miles per year, so I change the oil annually. Should I change it before the winter lay-up, when the fresh oil will sit in the dirty sump for six months? Or should I change it after the lay-up, so the new oil will not have chance to deteriorate? James Stainer, Lancaster A It’s probably best to drop the old oil at the end of summer, just before you lay the car up. Not only does this prevent the slightly acidic and contaminated oil sitting in the engine all winter, but it also stops the carbon and other contaminants settling into sludge in the bottom of the sump.