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road and workshop

19th November 1971
Page 58
Page 58, 19th November 1971 — road and workshop
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Which of the following most accurately describes the problem?

Bench wise: lathe sense 28

by Handyman

IN ORDER to make the system of diagnosis procedure work, it is necessary to make a rather elementary approach, or so it may seem. First the coolant level in the radiator should be checked against a known correct level, allowing for the expected expansion and subsequent drop. If the level is low, top up to the correct level. Where the engine has just overheated allow it to stand until the boiling has stopped, and the gauge reads under 200deg. F. before removing the pressure cap — and remember the earlier safety note: move the cap gently to the vent position, thus allowing any steam to. escape before complete removal.

Next add coolant if this is needed, but remember also that if the water is out of sight and probably below the cylinder head level, it is unwise to top up with cold water as there is the risk of fracturing head or block. Next inspect the pressure cap and its two valves, vacuum and pressure, also the gasket and seal, replacing if defective. Check the fan and water pump belt, looking for the faults we dealt with in the preliminary tests, i.e. slack belt, split or worn belt or worn pulley, and then adjust and/or replace.

Check for outside leakage around block head and radiator, then examine the oil level for low or unusually high condition — the latter can indicate water gaining access to the sump. Next check radiator and air passages, clean out and straighten any bent fins. All these tests being carried out with the engine stopped of course.

The engine can now be started for step No 2. Since the problem is overheating, first establish that the coolant level is still correct with the engine running, but get the temperature above 160/180 deg. F to be certain that the thermostat is open, then add or remove coolant to the correct level for normal operating. The vehicle temperature

gauge should now be tested by means of a second test thermometer in the top tank and if the dashboard gauge is faulty it must be replaced. Now the radiator core; with the thermostat now open, the core can be checked for any cold spots that would indicate partial clogging, and if clogging is in evidence, the cleaning procedure already described should be followed. The lower hose should now be checked for any tendency to collapse during sudden acceleration, which would be caused by the pump pulling against a choked radiator, or a blockage earlier in the circuit of the water flow. A further test is to check the pumping pressure and to do this you need to grip the top hose by hand first with the engine idling to get the feel of the hose at nil pressure, then run up the engine to its safe maximum speed and note the increasing hardness. If the hose was fa;rly soft to the feel when first gripped, and there is no increase in hardness as the pump is speeded up, then both the thermostat and the water pump should be examined for operating efficiency. Where one is dealing with overheating on a petrol engine, it pays not to overlook the carburetter mixture, as too lean a mixture can cause the engine to overheat. To check this, run the engine up to a safe continuous speed and then gradually pull out the choke; if the engine speed begins to increase, the .mixture is too lean and adjustment is necessary.

Coolant foaming can mean air entering the system, and with the engine temperature at around 180 deg. F run the engine up and watch the water in the top tank. If foaming occurs, replace the coolant and repeat the test to confirm the fault. Also with the radiator cap removed, watch for abnormal coolant rise when accelerating sharply and running at normal maximum. If the rise is abnormal, follow the overflow loss diagnosis described earlier. Now, with the engine running to heat up the coolant, note whether the level drops before the coolant boils; if the level does drop, follow the leakage procedure.

Where the engine boils with the coolant up to its level, follow the procedure described under overheating with no loss. Determine the diagnosis procedure to be followed for the particular coolant condition found, but remember when having made the necessary fault correction, always carry out a final, good road test to establish that all is now normal and no secondary fault has developed.

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