Cooling System Issues:
* Air in the cooling system: This is a very common problem after radiator or thermostat replacement. Air pockets prevent proper coolant flow, leading to overheating. Bleeding the cooling system is crucial. Different cars have different bleeding procedures; consult your owner's manual.
* Faulty water pump: The water pump circulates the coolant. A failing pump won't move coolant effectively, causing overheating. Listen for unusual noises (whining) from the pump.
* Clogged radiator: While you've replaced the radiator, debris could still be present in the system, particularly if a thorough flush wasn't performed before installation.
* Radiator cap malfunction: A faulty cap won't maintain proper system pressure, hindering efficient cooling.
* Head gasket failure: A blown head gasket allows coolant to mix with engine oil or enter the combustion chamber, leading to overheating and other symptoms (white smoke from exhaust, milky oil). This is a serious issue.
* Incorrect thermostat: Make sure you installed the correct thermostat for your vehicle's specifications. An incorrect thermostat can cause improper coolant flow.
* Cooling fan malfunction: The cooling fan helps dissipate heat, especially at low speeds. A faulty fan or its relay/fuse can lead to overheating. Check if the fan is coming on when the engine gets hot.
* Faulty temperature sensor: An inaccurate temperature sensor could give a false reading, leading you to believe the cooling system is working when it's not.
Other Potential Issues (Less Likely):
* Low coolant level: Even after filling, a leak somewhere in the system could be causing the coolant level to drop, resulting in overheating. Check for leaks carefully.
* Blocked coolant passages: Internal passages in the engine block or radiator could be clogged, restricting coolant flow. This is less likely after a radiator replacement, but possible if the old radiator's failure was due to internal blockage.
Troubleshooting Steps:
1. Bleed the cooling system: This is the *first* thing to do.
2. Check coolant level: Make sure the coolant reservoir is filled to the correct level.
3. Inspect for leaks: Look carefully for any leaks around hoses, clamps, the radiator, and the water pump.
4. Check the cooling fan: Make sure it turns on when the engine gets hot.
5. Check the radiator cap: Ensure it's functioning correctly.
6. Listen for unusual noises: A whining water pump is a common sign of failure.
7. Check the engine oil: Look for milky or foamy oil (indicating a possible head gasket problem).
8. Use an infrared thermometer: Check the temperature of various components (radiator inlet/outlet, engine block) to pinpoint areas of excessive heat.
If you've checked all of these and the car still overheats, it's best to take it to a qualified mechanic for diagnosis. Overheating can cause serious engine damage.
