Why is my Engine overheating?

Hello, Perform a pressure test on the engine cooling system first. If you have a leak, you will slowly, or quickly, lose pressure, and you should be able to see where coolant is leaking from. Also, if the hose clamps are loose on the overflow tank, it may be leaking there still. Next, if the system is without leaks but still overheats, you may have a waterpump issue. A semi-decent way of detecting if the waterpump is functioning is to raise the engine speed when the engine starts to get hot. If the engine cools due to the water pump forcing circulation through the radiator, it should be fine. However, raising the engine speed slightly causes more heat, you likely have a bad water pump. Now, this may just be an issue of having air left in the system, and ensuring that all coolant system bleeding procedures are followed (if any) is detrimental to the function of the thermostat.