I have an 18 year old 2004 Grand Prix GTP with 70k miles that, over the last 2 years, had started to lose significant gas mileage. When new, if I did a granny run at 55MPH on the highway, I could see 34-36MPG. That had dropped all the way down to 24. Instead of 25-27 combined, I was seeing 18.I changed out everything I could think of: new brakes, new hubs, transmission fluid/filter, air filter, fuel filter, coolant flush, new plugs, supercharger oil, Techron additive. Gas mileage was still in the toilet.I then tried a can of Seafoam. 5oz in the crankcase and the rest in the tank. First off, it cleared up a metallic scraping sound that my car was making on shut-down right away. Then, after about 100 miles of driving, my gas mileage came back. Pic is of a 55MPH highway run. 33MPG! My combined is at 27.This car had had regular oil/filter changes, always with full synthetic oil; but apparently that wasn't enough to keep it from gunking up with the car's infrequent use. One can of Seafoam brought it back to within a few percent of new.
Rating:
[5 of 5 Stars!]