I've heard plenty of good things bout it, but I haven't heard for sure wether it was a good idea to use it on a high mileage engine. I mean yeah I know its supposed to clean it out and all, but you know the old saying "if it's not broke don't fix it." Its a '95 Tbird 4.6L with 154K on it. never used any cleaner throught it, and I've had it since 44K. Used plenty of fuel injector cleaner and Slick 50 every 15K to 20K. Another part that worries me is I have this clicking type noise, that a mechanic said was a wrist pin. And today I noticed 3 times that I spit out some blueish colored smoke after taking off from some stop lights. But it only did it those 3 times, I didn't notice it at any of the other stoplights. Thanks for your opinions!!!