Lesson 3/Learning Event 1
you imagine how much the unnecessary cost would be if you or someone else were to mistake valve noise as
being a loose rod or main bearing? This is why a mechanic with a lot of experience will sometimes get other
mechanics to listen to a noise in an engine. Then they talk it over before deciding what the trouble is. Any
noise that the engine does not normally make should be investigated. Find out where the unusual noise is
coming from. Then by using your knowledge of the construction and operation of the engine and referring to
technical manuals, decide what is causing the noise.
Engine Temperature
By the time you have run an engine long enough to check it out for noises and pressure leaks in the coolant
and lubrication systems, the engine should be warmed up to its normal operating temperature. Check the
temperature gage reading; then look in the maintenance manual to see what the normal operating temperature
is for the engine you are working on. Generally, 180F will be the normal operating temperature for military
vehicles.
If the temperature gage pointer is at the very bottom or top of the scale, either the gage or wiring is probably
bad. If you suspect that a gage is faulty, check its reading with an antifreeze hydrometer. This instrument is
normally used to check the strength of the antifreeze solution in the cooling system. But, it also has a
thermometer to indicate the temperature of the coolant. By filling the hydrometer with coolant from the
radiator, the coolant temperature will be shown on the thermometer. Compare this reading with the
temperature gage reading. Any big difference in reading will indicate that the temperature gage is not reading
correctly.
When you remove the radiator cap to use the hydrometer, be very careful. The coolant expands as the engine
warms up, so pressure builds up in the cooling system. Removing the radiator cap lets the pressure escape. If
the engine happens to be very hot, boiling water and steam can fly out past the cap and scald you seriously.
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