You guys, this really blows. My truck has been running great giving me absolutely no problems lately. However, I took it out on the highway today, probably the first time it has been on the interstate in 4 months. Anyways, I couldn't even get to my destination, which was 15 miles away, without running it up into the hot zone, past the normal. When I returned, I flushed and cleaned the whole system, as I discovered that there was more radiator sealer in my water then there was coolant. Anyways, this was a good flush, and I flushed it until the water was totally 100% clear. I filled it about 50/50 and drove it around. It stayed fine in the city but as soon as I would really put a load into the motor, the temp would head north. WAY NORTH. So now I don't know what to do. I am going to put a new thermostat in it tomorrow, but if that don't fix it then I don't know what else. I know my cooling system has the capacity to cool this truck off because I pulled a 3 ton trailer 400 miles through some of the hilliest terrain without any problems. Which is why this confuses me. My brother said something about putting some vinegar in my cooling system and then draining it at the end of the summer. I am gonna have to drain it regardless as I have more water in it than coolant. But I need help guys. Thanx