Notice: Exhaust gasses may enter the cooling system through a leaking cylinder head gasket. Exhaust gasses combine with water to form acids. These acids are harmful to the cooling system and the engine.

In order to check for exhaust gases leaking into the cooling system, do the following steps:

1. Drain the cooling system to a level just above the top of the cylinder heads.
2. Disconnect the radiator inlet hose.
3. Remove the thermostat.
4. Remove the fan belt.
5. Start the engine. Accelerate the engine several times.
6. Note any detectable coolant rise or bubbles in the coolant. These may indicate that exhaust gases are leaking into the cooling system.

In order to check the operation of the coolant pump, do the following steps:

1. Start the engine.
2. Squeeze the radiator inlet hose until the engine warms. When the engine warms, you should feel a pressure surge.
3. Check for a plugged vent hole in the coolant pump.

In order to test for restrictions in the radiator, do the following steps:

1. Start the engine. Wait until the engine reaches normal operating temperature.
2. Turn off the engine.
3. Feel the radiator. The radiator should be hot along the left side and warm along the right side, with an even temperature rise from right to left. Cold spots on the radiator indicate clogged sections.

Restrictions in the cooling system can cause engine overheating or cooling system noise. The following components are affected by these conditions:

The following are symptoms of these conditions:

1. Isolate the blocked area by probing the engine with a sounding bar (large screwdriver).

Caution: Under pressure, the temperature of the solution in the radiator can be considerably higher, without boiling. Removing the radiator cap while the engine is hot (pressure is high), will cause the solution to boil instantaneously, with explosive force. The solution will spew out over the engine, fenders, and the person removing the cap. Serious bodily injury may result. Flammable antifreeze, such as alcohol, is not recommended for use at any time. Flammable antifreeze could cause a serious fire.

2. Remove the radiator cap.
3. Observe the coolant being circulated in the radiator. Feel for cold spots on the front area of the radiator that could indicate blockage. Blocked radiators generally occur on vehicles with high mileage and not on new vehicles.
4. Check if the thermostat is opening properly.
5. Check the coolant outlet for any blockage.
6. Remove the coolant pump from the vehicle.
7. Remove the back cover of the pump. Inspect all of the internal passages using a flashlight.
8. Inspect the crossover at the front of the intake manifold. You can only see the entire passage of the crossover with the thermostat removed.
9. Remove the cylinder heads. Check the engine block using a pen light flashlight. Do not replace a block unless you can see the restricted area.
10. Inspect the cylinder heads if the problem is not found. Cylinder heads with blocked coolant passages generally have more than one blocked area. Look for signs of overheat discoloration (a dark blue or black area). If no discoloration is found, look in the coolant passages for blockage and probe all of the accessible passages. You cannot reach all of the passages because the cylinder head is intricate. Using a substantial wire, go through or around a partially blocked area. If nothing is found by visual inspection and probing, inspect the passages for a rough, ragged appearance. The roughest internal passages are most likely blocked. Replace a blocked or suspect cylinder head. Inspect the replacement cylinder head before installation.