* Radiator: You suspect this, and it's a very likely problem given its age. A radiator can become clogged with debris, rust, or scale, significantly reducing its cooling capacity. Even if it *looks* okay, the internal passages might be severely restricted. This is especially likely to cause overheating at idle where airflow through the radiator is minimal.
* Cooling System Leaks: Even with a new water pump, there could be a small leak somewhere in the system (hoses, radiator, etc.) causing a slow loss of coolant. This would lead to overheating, particularly at higher RPMs where coolant flow is increased. Check all hoses carefully for cracks, bulges, or leaks. A pressure test on the cooling system is recommended.
* Fan Clutch (if applicable): You mention an *electric* fan, but if there's also a clutch fan, its operation needs to be checked. A malfunctioning clutch fan won't engage properly and provide sufficient airflow, especially at lower speeds.
* Head Gasket: A blown or leaking head gasket can allow combustion gases to enter the cooling system, raising pressure and causing overheating. This often shows up as milky oil or white smoke from the exhaust. Check your oil for signs of milky discoloration (mayonnaise-like substance).
* Water Pump Installation: While you've replaced it, ensure it was installed correctly. An improperly installed water pump won't circulate coolant effectively.
* Thermostat Housing: A crack or blockage in the thermostat housing itself could restrict coolant flow.
* Wiring/Sensor Issues (Electric Fan): Confirm that the electric fan is turning on at the appropriate temperature. Check its wiring, fuse, and the temperature sensor that controls it. A faulty sensor could prevent the fan from turning on when needed.
Troubleshooting Steps:
1. Thorough Radiator Inspection: This is the most likely problem. If possible, have a radiator shop pressure test it to check for leaks and internal blockages. Consider replacing it.
2. Pressure Test the Cooling System: This will identify any leaks that might not be visually obvious.
3. Check for Leaks: Carefully inspect all hoses, clamps, radiator connections, and the water pump for leaks.
4. Inspect the Fan Clutch (if applicable): Make sure it engages properly when the engine is running.
5. Verify Electric Fan Operation: Ensure it's switching on when the engine reaches a certain temperature.
6. Examine the Oil: Check for signs of milky discoloration (emulsion) indicating a possible head gasket issue.
7. Inspect Thermostat Housing: Look for any cracks or signs of blockage.
If you've done all the above and are still having problems, it's best to consult a mechanic specializing in older vehicles. They have the experience and tools to diagnose more complex issues. Overheating can cause serious engine damage if not addressed promptly.
