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5th November 1971
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Page 42, 5th November 1971 — road and
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Which of the following most accurately describes the problem?

workshop by Handyman

Benchwise: coo/it (26)

WHEN engine overheating occurs it is best not to blame the cooling system right away but rather to investigate all possible causes, because overheating can be caused by units outside the cooling system itself. However, in approaching the problem we must first recognize that there are three general forms of overheating and it is necessary first to determine which of the three actually applied before the overheating began. We have coolant loss via overflow pipe, coolant shortage from leakage, and a situation of overheating but no coolant loss. A good deal of valuable time can be saved by being able to pinpoint which condition applied before boiling.

All causes of overheating lead to violent boiling and coolant loss, therefore it does not do to assume that coolant shortage was the original cause merely because the coolant is low when overheating is

discovered. To be certain whether coolant shortage is the real cause, or whether it resulted from overheating, the investigation must start with the coolant at the correct level in the radiator and the temperature well below boiling point. The engine can then be operated until overheating begins, and during this period of operation it can be determined if leakage or overflow loss occurs before coolant loss.

Examination

A complete examination and search for cooling system trouble, including tests and inspections, need take very little time and little mechanical work is called for. Obviously, it is better first to run the engine with the vehicle stationary as the trouble can then be located more quickly in a typical case.

Therefore, check No 1 is to stop the engine and examine both engine oil and coolant levels; also carry out a general check for any leakage and make an examination of the fan belt, radiator cap and air passage through the radiator core.

Check No 2 calls for the engine to be run to determine which type of overheating exists and inspection of the coolant level to note whether it rises or falls before overheating starts; at the same time the coolant temperature should be watched closely with a thermometer placed in the tank of the radiator.

The type of overheating is determined by observing whether coolant shortage from overflow loss or from leakage takes place before boiling. Following this the correct procedure can be selected for diagnosing the particular type of overheating found, assuming that the cause had not already been located in checks Nos 1 and 2. As the preliminary diagnosis was made with the engine in neutral and under no load, its usefulness can be somewhat limited, therefore a road test which copies operating conditions may be called for.

To carry out the road test a catchpot is needed — this should be a gallon can or jar, installed in the cab and piped to the overflow; the container end of the pipe should go at least lin. into the catchpot.

The vehicle should now be operated, selecting a high gear as soon as possible to provide load, and the throttle opening gradually increased while watching the temperature gauge and checking for coolant being discharged into the catchpot. Make one or two stops and with engine running at a fast tick-over check for a drop in coolant level not accounted for by coolant collected in the catchpot, to determine whether there has been any loss by leakage. If the level is Out of sight it can be checked with a rubber hose attached to the drain cock as follows.

Shut off engine, attach length of hose to drain cock, remove radiator cap and hold end of hose above radiator level, open the drain cock and then gradually lower the hose below the top of the radiator. The water will begin to flow from the hose at the exact height of the water level in the radiator. Continue the abcive steps, but before overheating and boiling occur it is necessary to determine whether coolant shortage preceded overheating and if so whether this shortage was caused by overflow loss or leakage. The amount of coolant in the catchpot indicates the overflow loss, so when the original coolant level is not restored when pouring the overflow coolant back into the radiator, the difference between the original and final level represents leakage loss. If there is no drop in coolant level before overheating occurs, shortage of coolant can be disregarded as the primary cause.

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