The extra load causes the engine to run hotter. If it doesn't do this when you are not towing, chances are the thermostat is good. That would lead me to believe the radiator is partially plugged and can't cool the engine fast enough with the extra load. Start with flushing the cooling system. It wouldn't hurt to replace the thermostat when you do it.
Let me know if you have other questions.
Friday, June 19th, 2009 AT 5:41 PM