[tomthedog]

great post THUMB. keep in mind everyone, the biggest by-product of combustion is water. as water evaps at a low temp, it leaves all the stuff it was holding (think of hard water drying on the paint, you end up with waterspots) in the oil/eng. it norm takes almost 1 hour of driving to heat the oil enough to boil off the water (witch holds the "junk" that can mess up the eng) out of the oil. the HARDEST thing your eng does is city driving. this is why the maint book says to change the oil at 3K's for "HARD" driving (5-7K's for i-state driving). while modern eng oils can last for 7K's+, the stop and go/short trips of city driving fill up the add packs like THUMB stated. even if you use full synth, this can still happen. if you drive in city, just use reg oil and change every 3K's. happy mototing.