I have an older model 997 ztrak mower. after mowing about an hour an alarm starts going of and the mower cuts off. Engine still running. I have done all the tests and checks that I know of but cannot get this solved. things I have checked are: 1-coolant level, 2-water pump, 3- blew out radiator coils and oil cooler. 4. oil level, 5. thermostat, all are good. any suggestions?