DougM,<P> The reason that you would use a lower opening thermostat in an offroad vehicle is that the OEM requirement is for on road use in the country of manufacture. Mitsu is from Japan and most of the offroading is done on trails that are like fire cuts so the engine will not work as hard and not heat up as fast. The lower thermostat rating is for the opening time of the cooling system. Yes it may be a little harder on the fuel mileage rating but the safety margin on a working engine is increased. I know you don't agree with me but I have experienced an improvement in engine life with a lower temp thermostat. BTW in the trucking industry it is common practice to run a thermostat 10 degrees cooler in trucks that run over the Rockies on a regular basis. They haven't gone boom because of it. Also if Rudolfo runs coolant (ethylene glycol or antifreeze) in his rad as well as water he will notice the engine doesn't get as hot. It seems though his main issue was with a bad rad. It might be a good idea to make sure that he uses distilled water as it is common for the regular untreated tap water to contain minerals that will "scale" the rad. Also to be on the safe side he can get additives to prevent scaling that go in the rad or he can buy coolant that has these additives in them already.