Possible Causes:
* Air in the Cooling System: This is the most likely cause if you just installed a new radiator. Air pockets prevent proper coolant circulation, leading to overheating. Even a small air bubble can cause a hotspot and damage. The system needs to be properly bled (de-aired) after installation.
* Improper Radiator Installation: Did you correctly connect all hoses and ensure the radiator is securely mounted? A leak, even a small one, will cause overheating and can lead to engine damage. Double-check all connections.
* Water Pump Failure (Less Likely, but Possible): A malfunctioning water pump can't circulate coolant effectively, resulting in overheating. This is less likely if the engine was working fine before the radiator change.
* Thermostat Issues: A stuck closed thermostat will prevent coolant from flowing.
* Head Gasket Failure (Serious): Overheating can cause the head gasket to blow, allowing coolant to mix with oil or enter the combustion chamber. This is a major repair. Symptoms can include white smoke from the exhaust, milky oil, or loss of coolant.
* Other Cooling System Leaks: Check all hoses, clamps, and the radiator itself for leaks.
Why Not Start the Car?
Attempting to start the car again before addressing the overheating issue could cause further damage:
* Seized Engine: Severe overheating can seize the engine, requiring a costly rebuild.
* Head Gasket Damage: As mentioned, starting the engine could worsen head gasket damage.
What to Do:
1. Let the Engine Cool Completely: This is crucial. Do not attempt anything until the engine is completely cold (several hours).
2. Check Coolant Level: Carefully check the coolant level in the overflow tank. If it's low or empty, you have a leak.
3. Inspect for Leaks: Visually inspect all hoses, clamps, the radiator itself, and the water pump for any signs of leaks.
4. Bleed the Cooling System: If you haven't already, you *must* bleed the air from the cooling system. The procedure varies depending on your car's make and model; consult your owner's manual or an online guide specific to your vehicle.
5. Check the Thermostat (if accessible): Make sure the thermostat is opening and closing correctly.
6. Check the Oil: If the oil is milky or has a brownish sludge-like consistency, it strongly suggests a blown head gasket.
7. If you find leaks, repairs, or don't know how to bleed the system, do NOT attempt further troubleshooting. Take your car to a qualified mechanic. Ignoring overheating can lead to very expensive repairs.
In short, don't risk further damage. A mechanic can diagnose the problem accurately and safely. The cost of professional diagnosis and repair is far less than the cost of a severely damaged engine.
