"Anti-freeze Better Than
Page 57
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Draining "—L. J. Cotton
Because of the Possibility of Failing Completely to Drain a Radiator, and the Build-up of Salt Deposits, Nightly Emptying in Winter is Better Avoided
AN outstanding case for the use of anti-freeze solutions in winter, rather than draining the cooling system nightly, was made out yesterday by Mr. L. .I. Cotton, technical manager, cars and commercial vehicles, Unilever, Ltd.
He was opening the 1958-59 lecture session of the Institute of Road Transport. Engineers in London. Speaking on " Summer and Winter Protection Against Corrosion in Engine Water-cooling Systems," he pointed to the dangers of using tapor rain-water without the addition of anti-freeze solution or inhibitors.
Problems which could arise from nightly draining included the difficulty of completely emptying the system when taps became partially blocked, or where bad design or the fitting of a heater caused pockets of water to remain in the system.
Moreover, unless the water used for refilling was soft, a continuous deposit of hard salts occurred. This altered the heat-transfer rate from the metals of the engine and blocked the water passages, to cause overheating and adversely affect performance. Rain or surface water supplies could also vary. For example, in some areas rain-water could have an acid content, which would cause corrosion in the cooling system whilst in other areas surface water contained chloride, which could also corrode -metal.
Waste of Time
Regular draining exposed the internal cooling surfaces of the engine to air and thus allowed oxidation to take place. Without anti-freeze, the radiator could still freeze when driving into a high wind with an air frost. Time was also wasted in draining and refilling the engine, which could otherwise be used for additional operation of the vehicle, whilst the provision of heated garages or an external steam heating system was extremely expensive.
Even though some of these problems could be overcome by adding a separate inhibitor to the cooling liquid, a suitable anti-freeze solution had greater advantages. .
To be completely effective, the solution should have a viscosity no greater than that of water; should be suitable for mixing with any other anti-freeze compound and be safe in solution with tapwater. Primarily it should give complete protection against freezing of the coolant and allow a vehicle to be driven away immediately the engine was started under any condition, whilst making no reduction in the heat-transfer rate.
Its anti-corrosion properties were of great importance, as it should cause no deterioration in hoses made of rubber or synthetic materials, and not corrode metals. It should also withstand leakage of exhaust gases into the coolant and be suitable for use in all types of car, commercial and industrial engine.
Other desirable properties were that it should be non-inflammable and nonvolatile, and have a distinguishable colour. The perfect anti-freeze solution was, however, not yet available.
Two types of anti-freeze compound were commonly used. One had a high boiling point and contained methanol. This was sold in America. It was cheap and had a low viscosity, but these advantages were outweighed by a high rate of evaporation and the possibility of the production of toxic fumes, coupled to an added fire risk.
Solutions with high boiling points which were widely used in Britain normally contained ethylene-glycol, prophylene-glycol and glycerol, • these being grouped chemically as polyols. All anti-freeze solutions containing these chemicals shared a high flash-point and an evaporation point above that of the engine coolant.
Increased Viscosity
Glycol and glycerol had a tendency to seep through small apertures and thus might increase coolant leakages. Moreover, all this group of compounds increased the viscosity of the coolant, thus reducing the beat-transfer rate, and could cause overheating before radiator boiling became apparent.
As the three compounds of the solutions with high boiling points could be broken down chemically into organic acids, which caused rapid corrosion of the metallic parts'of the engine and electro-chemical corrosion of dissimilar metallic parts, inhibitors were added to the solutions to make them more innocuous than water.
These inhibitors generally took three forms. Phosphates or soluble oils could be used to form a protective film over metal parts of the cooling system.
Another approach was to add alkaline chemicals, such as borax, to the liquid, thus neutralizing any acidity which might arise. To eliminate the problem at source chemical combining agents were used to prevent decomposition of the anti-freeze liquid.
The most suitable inhibitor for any type of engine depended on the metals employed in the construction of the unit and on the kind of operation. Engines working at continuous full load were more prone to breakdown of the antifreeze solution and subsequent damage than were lightly stressed units.
To obtain the greatest benefits from anti-freeze and inhibitors, the engine manufacturer's recommendation should be sought as to the most suitable preparation to use. Drivers and maintenance staff alike should have impressed upon them the use of anti-freeze as a means for preventive maintenance.
It was particularly important that the cooling system should be thoroughly cleaned before the introduction of either anti-freeze solution or inhibitors. All hose connections and similar points where leakage could occur should also De checked. Cylinder-head nuts should he pulled down to their correct torque rating to eliminate the possibility of leakage of exhaust gases into the coolant: thus causing its rapid deterioration.
If too little anti-freeze were used, ice crystals might 'form, producing a mush which could cause blockages in the system. On the other hand, too much glycol anti-freeze would raise the viscosity of the coolant and might precipitate serious overheating.
Altering Properties The maximum concentration of an ethylene-glycol-based anti-freeze used in this country would not exceed 35 per cent, of the volume, giving protection against 42° of frost. Up to 50 per cent. might be used overseas to cater for 69° of frost. The maximum permissible concentration was 55 per cent., as arty further increase would alter the chemical properties, of. the coolant and actually could give reduced protection against freezing. a
Anti-freeze should be added to the system at the end of the summer and removed in the spring. By this time, the inhibitors in the solution would probably be depleted.
It was a pity to offset the advantages gained in the winter with inhibited antifreeze by using plain tap-water during the summer. The use of a proprietary inhibitor with tap-water would continue to keep the engine clean, particularly in districts where the mains water was notoriously " hard," and deposits would, consequently, form rapidly.
Where chemical laboratory facilities were available, checks of the anti-freeze solution for any trace of chemical breakdown or the existence of "suspended solids" in the coolant would provide valuable guidance to the condition of the mixture. Mr. Cotton foresaw the day when maintenance staff would have simplified equipment for making such checks.
An interesting point discussed was that as leakage of exhaust gases into the cooling system produced a rapid chemical breakdown of the anti-freeze solution, it was possible, by coolant analysis, to discover cylinder-head gasket failure some time before symptoms became apparent in operation.
If vehicle manufacturers dispatched new vehicles with either inhibited water or anti-freeze solution in the cooling systems, and if such compounds were used throughout the life of the vehicles, defects such as blocked radiators would, in all probability, become a thing of the past.