Overheating
1. Insufficient coolant in the system
2. Water pump drive belt defective or not adjusted properly
3. Radiator core blocked or radiator grille dirty and restricted
4. Thermostat faulty
5. Fan blades broken or cracked
6. Radiator cap not maintaining proper pressure. Have the cap pressure tested by gas station or repair shop.
Overcooling
1. Thermostat faulty
2. Inaccurate temperature gauge
3. Wrong thermostat (too cool range)
External coolant leakage
1. Deteriorated or damaged hoses or loose clamps. Replace hoses and/or tighten the clamps at the hose connections
2. Water pump seals defective. If this is the case, water will drip from the weep hole in the water pump body
3. Leakage from the radiator core or side tank(s). This will require the radiator to be professionally repaired.
4. Engine drain plug leaking. Water jacket core plugs defective.
Internal coolant leakage
Note: Internal coolant leaks can usually be detected by examining the oil. Check the dipstick and inside of the valve cover for water deposits and an oil consistency like that of a milkshake.
1. Leaking cylinder head gasket. Have the cooling system pressure tested.
2. Cracked cylinder bore or cylinder head. Dismantle the engine and inspect
3. Intake manifold gasket leaking
Coolant loss
1. Too much coolant in the system
2. Coolant boiling away due to overheating
3. External or internal leakage
4. Faulty radiator cap. Have the cap pressure tested.
Poor coolant circulation
1. Inoperative water pump. A quick test is to pinch the top radiator hose closed with your hand while the engine is idling, then let it loose. You should feel the surge of coolant if the pump is working properly
2. Restriction in the cooling system. Drain, flush and refill the system. If necessary, remove the radiator and have it reverse flushed.
3. Water pump drive belt defective or not adjusted properly
4. Thermostat sticking