* Water Pump: A failing water pump won't circulate coolant properly, leading to overheating. You might hear unusual noises (whining, grinding) from the pump if it's failing.
* Thermostat: A stuck closed thermostat prevents coolant from circulating until it reaches a very high temperature. This will cause the engine to overheat quickly. A stuck *open* thermostat can also cause problems, but usually leads to poor engine warming and potentially lower-than-ideal operating temperature, not necessarily immediate overheating.
Other possibilities:
* Coolant leaks: A leak in the radiator, hoses, or head gasket will cause the system to lose coolant, leading to overheating.
* Low coolant level: Simply having low coolant will cause overheating. Check your coolant level first!
* Radiator fan: A malfunctioning radiator fan will prevent proper heat dissipation, leading to overheating, especially at idle or low speeds.
* Clogged radiator: A radiator clogged with debris will restrict coolant flow and cause overheating.
Troubleshooting steps:
1. Check the coolant level: This is the first thing to do. Add coolant if it's low (after the engine has cooled down completely).
2. Inspect hoses and radiator for leaks: Look for any visible cracks, holes, or signs of leakage.
3. Check the radiator fan: Make sure it's turning on when the engine gets hot.
4. Feel the upper and lower radiator hoses: When the engine is running, the upper hose should be hot, and the lower hose should be warm. If both are cold or only the upper is hot, there may be a problem with circulation (pointing to the water pump or thermostat).
Only after checking these should you consider replacing the water pump or thermostat. Replacing the wrong part is a waste of time and money. If you're not comfortable diagnosing the problem yourself, take it to a mechanic for proper diagnosis and repair.
