Have you had any work done on the unit that would require a coolant change? I any thinking check for an air lock in the cooling system. Since you found out where the radiator is now check to make sure the fan is working on it and check the temp of the radiator compared to the engine. Are they both getting close to 245 Degs. If the radiator is not as hot as the engine, coolant is not flowing (air lock or plugged radiator). You don't need to wait until it is 245 to find this out so shut down the generator before that temp. If these don't help you have engine problems.