A stuck closed thermostat will cause this. If the engine has ever overheated then the thermostat must be renewed. This is because the high temperature will cause the wax in the thermostat to get very thin and subsequently lost. The thermostat then will not open. It's a very good idea to change the thermostat every two or three years in any case.

Another thing to check is the condition of the radiator. Make sure the fins are in good condition and not corroded. The radiator cannot correctly dissipate heat if they are, leading to overheating. Also something that is well known with plant equipment but no less necessary and often ignored on cars is to make sure the radiator is clear and not full of dust and dirt, which would prevent airflow and seriously affect heat dissipation. Use and airline and blow through the radiator fins.