generator overheat, any ideas??

2004 holiday rambler.. 7500 onan diesel. Going down the road will run about 30-45 mins sitting in the driveway about 15mins then shut down...it flashes the 1 code then the 3-3 code for over heat shut down. Pulled the top cover off nothing out of place. Belt doesn't feel loose. Plenty of fluid..no obstructions.. washed the coils on the radiator out.. cleaned out the spark arrestor...if you open the cap with it running it shoots a straight stream of coolant out.. not sure if this is normal or not.. I want to look in filler neck and see if the fuild was moving but you can with it shooting out like that..also every time it shuts down like that when you power out back up you have to beat on the tranfer switch to get power back in the coach.