I seriously doubted many claims about you product but I tried it. A year ago I bypassed a badly leaking heater while on a trip. One year later I bought some Kseal and added it too my overflow tank which looked like coffee. After running the engine for 1/2 hour and no issues I shut it down for another 1/2 hour. Than I drove 50 miles to test it and there were no drips onto the passenger carpet or any overheating. I also noted that I could still smell coolant and see some steam on the lower windshield. I attributed that to the fact that it has been bypassed for a year. So far I have to say that I do believe that your product has sealed my heater core and that now I can drain and refill the cooling system and replace the T stat because my heating was sporadic during my trip. Your product did not affect the operation of my cooling fan during the process and there was no smell under the hood or boiling sounds during my trip or after whenever I parked. So this sceptic is a believer and you can use my testimonial if you wish.