Lesson 3/Learning Event 1
On the other hand, if the engine is warm and no pressure escapes when the radiator cap is released, there is
probably a leak somewhere in the cooling system. If you found no water leaks, the pressure may have leaked
above the water level. One place it can do this is through either one of two valves in the radiator cap. Both
valves are held closed by a spring. One relieves the system of excess pressure, while the other valves allow
outside air to enter the radiator after the engine is stopped and the water cools off.
If the engine actually gets too hot, it could be caused by some internal problem, such as a thermostat or a leaky
head gasket, but you should look for more simple faults first. For instance, is there anything that reduces the
amount of airflow between the radiator fins? These fins collect heat from the water passing through the
radiator, then air cools the fins. So, inspect the radiator core for bent fins or being stopped up with leaves or
brush. Anything that reduces airflow must be corrected before doing a lot of other repair work in an attempt
to correct overheating problems.
Road Test
If the condition of the vehicle will allow you to operate it on the road, a road test should be performed. Some
of the questions about engine operation that a road test should answer are: does the engine develop full
power? Does it accelerate properly? Are there any unusual noises as the engine is operated under different
load conditions? Does it run smoothly? Does it smoke excessively?
Exhaust
The color of the smoke coming out the exhaust can be a clue to the cause of some engine troubles. Have the
driver speed up and slow down the engine while you watch the exhaust. If the engine is running normally and
is at operating temperature, the exhaust should be clear or a hazy gray. It may be white if the engine is cold.
The color of the smoke may be slightly black as the engine is speeded up, but, when run at a steady speed, the
blackness should disappear.
If the blackness does not go away, the fuel is not burning properly. The trouble could be in the air intake
system or carburetor. The vehicle should go to your support maintenance if the problem exists after you have
checked all of the things you should check, such as the air cleaner.
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