I understand its a waste of money to flush a well looked after engine. But I'm more so wondering if an engine flush is good preventive maintance as it would help signifigantly reduce the risk of a engine sludge problem, if one were to ever occur.... I do my own oil changes, but I've noticed that after I do an engine flush, my car runs alot better for the first couple K's. Also my oil changes are done every 6 000km, which is about 4000 miles.