Overheating

If you're sure that the cooling system is staying full/not leaking externally, Make sure that the cooling fan(s) (both if it has 2) are running at the radiator at normal temperature. You can try to crank the vehicle with the cooling system full & the pressure cap off - if you get a geyser while cranking, it may be an indicator of a cylinder head problem. There is also a chemical test kit sold at parts houses in which a test sample turns blue in the presence of combustion gasses (another indicator of a head problem)