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10th September 1971
Page 46
Page 47
Page 46, 10th September 1971 — road and workshop
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Which of the following most accurately describes the problem?

Benchwise: cool it (78) by Handyman THE HIGH coolant temperatures to which the pressure cap and its valves are subjected can bring on fairly early deterioration of the cap gasket. Also, the valves and the underside of the cap are exposed to the extremely corrosive effects of steam, and, of course, air in the top of the radiator tank. As the cap is located above the normal coolant level it enjoys virtually nothing in the way of rust protection from any inhibiter in the coolant, thus failure of the valves can occur from corrosion damage.

I mentioned in a previous article that small particles of rust and debris can interfere with valve operation, just as, in the same way, constant usage of the cap will thin out the gasket and slacken or damage the cap lock mechanism. Any air leak above the water level in the radiator, such as at the cap gasket or valves, will prevent pressure from building up, and the value of the sealed system is lost.

Pressure valve Similarly, if the pressure valve is seized in the shut position, the pressure increase could be too much for the hose connections or radiator tank seams, and any failure of the vacuum valve to open could cause internal parts to collapse or close up a hose pipe. Remember too the tip about removing a pressure cap from a hot engine; if you must do it in a hurry, always give the cap just enough unscrewing movement to bring it to the vent position, and let any pressure escape there before removing the cap fully. Also, when refilling a radiator, avoid the rather rough trick of up-tilting a five or lOgal drum with a protruding neck and letting the drum thump down and rest in the filling orifice, as this can cut and destroy the filler neck seal and render the pressure cap useless.

Tied in very closely on a modern vehicle with a pressure cap is, of course, the

overflow tank, which, very briefly, can be described as a temporary storage tank for coolant that is forced from the radiator under working conditions or as the engine is stopped. The coolant returns from the overflow tank to the radiator as the engine cools. However, despite a very sound principle which really works, there are problems and faults or rather failures, one of which is that just like the radiator cap, the overflow tank is exposed to the effects of steam and air. Obviously the greater use of plastics is a step in the right direction towards getting over these problems.

Problems faced by users of a metal overflow tank include rusting and corrosion from the inside, as being empty most of the time the tank has no help from rust inhibiters in the coolant.

Condensation In winter the tank may not receive any coolant from the radiator, but does collect condensation in the connecting pipe and this has been known to freeze during periods of low temperature operation, specially when the tank is low sited and in the path of thrown-up slush. Here the trouble occurs a little later when, with the overflow tank in more regular use, it is likely that the connecting pipe will be found to have split.

The presence of an air leak in the overflow tank's feed pipe, its connecting points, or its own cap. will cause failure of the vacuum, preventing the return of coolant to the main tank.

So while these systems come under the heading of "Fit and forget" as far as water loss and topping up are concerned, the same need for the regular inspection remains in order to ensure that the system is airtight and free from obstruction.

Recently on a light vehicle suffering regular overheating and radiator cap trouble, the answer proved to be no more than the newly fitted bracket for a fog lamp, as the bracket had been clamped down on top of the connecting pipe to the overflow tank, cutting off entry and exit of coolant. and upsetting the system completely until released.

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