The indicator for over heating comes on whether we are pulling a load or not, and when we turn on the heater it will almost immediately bring the level back to normal whether we stop or continue to drive. Also get a whistle noise periodically whether driving or sitting still.

It may be time to replace the radiator (Item 7, below). Refill with a 50/50 mixture of the recommended antifreeze and distilled water. Add the proper amount of SCA to prevent damaging cavitation.

Common causes of overheating:

1. Insufficient coolant and/or air in the system. When the system is cool, check the radiator and overflow tank coolant level. If the level is low, start looking for leaks. Check for deteriorated or damaged radiator and heater hoses; e.g. cracks, pin holes, and clamps that leak under pressure. Also, look for bulges and collapsed hoses. Attach a cooling system pressure tester to the radiator, if necessary, to help locate leaks. Pressurize the system to 16 psi. Learn how to properly purge your cooling system of air--this can be crucial in some vehicles. On many Hondas, for instance, fill the radiator with coolant, until it comes out of the opened bleeder bolt. It's important to follow the exact procedure for draining and filling the cooling system in the Owner's Manual--they do vary and it's very important. Failure to do so can result in a warped head, blown head gasket, and the engine seriously overheating.

2. Air flow problems--leaves, bugs, dirt, feathers, or plastic bags blocking the flow of air through the radiator. Gently clean the radiator with a garden hose.

3. Radiator fan not operating properly--check fuses; Engine Coolant Temperature (ECT) Switch, not the ECT Sensor; and radiator fan relay. The cooling fan not operating properly is one of the most common reasons engines overheat.

If the coolant is low and/or there's air in the system, the ECT Switch may not turn the radiator fan on.

4. Radiator shroud does not seal tightly enough for the fan to draw air through the radiator. This can cause the engine to overheat, while the vehicle is stopped.

5. Faulty radiator cap--doesn't maintain proper pressure or one or more valves are bad. Test cap relief pressure with a radiator cap tester (KD 3700 or Stant 12270). On non-expansion tank systems, which are most systems besides Ford's, there are two valves inside the cap that can fail. One allows hot coolant to flow into the overflow tank, the other allows coolant to flow from the overflow tank to the radiator, as the engine cools. If the coolant can't flow back into the engine, there won't be enough coolant and the engine can overheat. It's best to use a high quality, preferably OEM, cap.

6. Faulty thermostat--sticking closed. Improperly installed thermostats are one of the leading causes of Hondas overheating.

7. Radiator core blocked--mineral build-up (phosphate scale) and corrosion are the most common causes.

8. Inoperative water pump--pinch the top radiator hose closed with your hand, while the engine is idling, then release it. You should be able to feel a surge of coolant, if the pump is working properly. Change the water pump every time you change the timing belt.

9. Improper grade of engine oil--higher viscosity oil generates more internal friction and heat. Synthetic engine oils have higher coefficients of heat than conventional oils, which allows bearings and engines to run cooler--use them.


In an emergency, set the heater to maximum heat, blower to high, and open the windows. The heater will act as another radiator and help lower the engine temperature.