They make some good products, and their guarantee is second to none.Kreen evaporates once engine gets heated, I have personal used it on a Benz with OM606 indirect diesel engine with almost 300k mi!es with great results. Have also used in Benz OM648 engine with direct injection and only 100k miles but it didn't had much improvement. The OM606 was sludged and had a morning injector knock and it was gone (used 1/2 qrt in diesel tank) By the way there is a no questions asked money back guarantee. You also get Kroil penetration aerosol free and it is the best you can buy. I have no financial interest in Karo Labs.