I always use that 5w-30 quaker state formulated for high mileage engines... I've used that about 5 straight oil changes and compared my emission numbers with the numbers I just got and there was a considerable drop in every category. (Sorry,I'm sounding like a commercial now).
Since I'm not spending $5 a qt. for synthetic oil - I save enough to get a K&N oil filter for each change (that could also be why it's running cleaner).
anyway
