CAUSES OF OVERHEATING.

King Country Chronicle, Volume XXVII, Issue 4458, 17 October 1933, Page 3

CAUSES OF OVERHEATING.

NUMEROUS POINTS TO WATCH. With very few exceptions all modern cars are capable of running under normal and even strenuous conditions of use with overheating of the water in the radiator, says H. W. Bourdon in the "Morris Owner." If the water boils, therefore, this irregularity is due either to something being out of adjustment, or to running conditions that can only be described as abnormal.

Abnormal running conditions may be exemplified by climbing long and steep hills in warm weather with a strong wind blowing from behind the car. In such cases it is conceivable that with or without a fan, very little air will pass through the radiator; certainly there will be less draught through it than under ordinary conditions, possibly not enough to carry off the heat as fast as the temperature of the water increases. The only thing to be done in such an event is to stop and allow the water to cool down, and, if water has been lost i'n the form of steam, to take the first opportunity of replenishing the radiator.

The chief cause of overheating under normal conditions, assuming there is sufficient water in the radiator, is an unduly slack fan belt, especially in warm weather, o'n a car with a cooling system and radiator designed for operating with a fan. The remedy is obvious, but here it may be said that there is no advantage, when adjusting a fan belt, in tightening it until it is as taut as a violin string. When a belt is correctly adjusted it should be just possible, when the engine is thoroughly warm and stationery, to turn the fan by grasping one of its blades firmly with thumb and first finger. If it can be turned thus when the engine is cold, it is too slack. After a slack belt the cause of overheating most freqeuntly encountered is a restricted flow of water circulation. This may be due, in the case of a car that has been in use for a long while, to deposits of lime in the cylinder jackets and radiator tubes owi'ng to the continuous use of very "hard" water. In those areas where the tap water is of this kind, rain-water should be used, if it is obtainable, in order to prevent "furring"—in fact, rain-water is preferable in any case. Restricted circulation may be due, alternatively, to a "kink" in o'ne of the rubber hose couplings between radiator end engine, or to a very "ancient" hose having disintegrated internally; the rubber lining may be loose and ragged, and more or less impeding the water flow. Faulty carburetter adjustment and improper use of the rich mixture control are among other causes of overheating; they result in an excessively slow-burning mixture entering the cylinders—a mixture that is either too rich or too weak in petrol. The fact that an unduly weak mixture will have this effect is not realised by many drivers, particularly those who, thinking they will economise to the utmost in petrol con-

sumption, fit an extra air valve and keep it open as far, as often, and as long as possible, without actually causing the engine to misfire. The slow-burning mixture that results is not only prone to cause the water to overheat; the valves will attain excessively high temperatures too, which leads to burning and pitting. I have no hesitation in declaring that an extra air valve is a fitting which only a very small proportion of motorists can utilise to any advantage, while the majority will do more harm than good by fitting and attempting to use one. The owner driver who imagines that the petrol consumption of his car is hot as low as it should be will be better advised to run it into a recognised service station for test and examination; if the carburetter is out of adjustment it is far better to have it put right than to fit a'n extra air valve to enable the irregularity to be corrected as a process of driving. After that digression, some of the other causes of overheating may be mentioned. They have concern with the orthodox processes of upkeep and imply neglect of the latter, or fautly adjustment. If the valves have tappet clearances too large or too small, overheating may be observed, though as a rule the first effect to be noticed will be loss of power. This latter symptom and overheating will be evident if the brake-shoes rub their drums when the pedal and hand lever are in their "off" position. Insufficient oil in the engine, broil of poor quality, will have similar effects, while overheating is encouraged by such diverse irregularities as radiator shutters being jammed by small stones or needing oil, an excessive overload of passengers or luggage, or both, and driving with the ignition lever retarded while the engine is forced up to high speeds by the use of the accelerator.