I've used it for several applications. It will do the same thing in a diesel. My jetta (the last one TDI) don't get too jealous here would get pretty consistently with the Ultra Low Sulfur Diesel 49mpg (before they changed to the new diesel in 07 I got 52) with the sea foam i'd get about 54mpg. I've also used it to clean out fuel systems on motorcycles that have had bad gas. Helps clean out carb jets when ran through. Quite nice stuff (but it is 8 bucks a bottle).