ive read some where that using products like slick 50 and STP do your engine no good at all, Briggs and Stratton the biggest engine manufacturer in the world tested these additives and the engine with no additives just your run of the mill oil lasted 20% longer on the test bed before failing compared to one that was running with em, they're study showed that your oil filter will remove around 95% of these additives out of your oil. money for old rope anyone???? i swear by a really good quality oil changed every 5k. jobs a goodun. :-p