Don't Let It Boil! By W. Roper Lindsay, M.S.A.E., M.1.R.T.E.
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How to Combat the Effects of Scale and Corrosion in the Cooling System, With a Few Words of Warning Regarding Anti-freeze Mixtures
IT frequently happens that after an engine has been reconditioned, there is a tendency for the cooling water to
boil at the slightest provocation. If a sound job has been made of the overhaul, and the timing of the valves and the ignition be correct, despite which boiling occurs at moderate engine speeds and loads, then a dirty and choked cooling system may be suspected.
Reverse flushing at mains pressure may not cure the trouble. Removal of the top and bottom tanks of the radiator and " rodding" each tube, is a lengthy and expensive process, and is, of course, impracticable with a honeycomb-type radiator. However, purging of the entire cooling system with strong chemicals may prove effective and time saving. If we know the causes of the blockage we can prescribe accordingly.
Deposits in the radiator and water jacket may originate from one or more sources. There is the usual "kettle scale" and, particularly when using water obtained in chalky-soil areas, there may be actual deposits of chalk. When radiators are drained every night to avoid freezing-up during frosty weather, the constant boiling of a fresh supply of water each day may result in heavy accumulations of scale after four or five months. In addition, there is the sedimentation due to formation of heavy oily sludge resulting from leakage past cylinder-head gaskets or, possibly, from cracks in the combustion chamber prior to them being detected and the head changed.
Pump Grease May Cause Sludge Deposits
In some engines, where a nonsoluble pump-grease is specified, over lubrication will force this grease into the cooling system, where it is carried around until deposited in some inaccessible crevice. Ordinary chassis lubricant, from a pressure gun used over-zealously, will escape and get churned up to form more sludge
deposits. Designers have long since resigned themselves to the fitting of pressure lubricators on water pumps : experience taught them that most operators, at the first opportunity, scrapped the old-fashioned, but proofagainst-excess-greasing . type, screwdown lubricator.
Other fruitful sources of coolingsystem inefficiency are anti-leak compounds. Those of the liquid, noncereal type, made by concerns of repute are perfectly satisfactory and harmless under normal conditions. They operate on the principle of the solids in the compound being carried indefinitely in solution in the cooling system, sinless carried, or steamed, out through the leak. Then they build up, and eventually seal the leak—and' they sometimes do this job very effectively.
Unfortunately, there is the possibility that, when the radiator is drained, some of this anti-leak compound may settle out, either in the restricted spaces A30
around the cylinder head and block, or in the header tank of the radiator. This is one reason why reconditioned engines persistently overheat. There is also the oxide sedimentation due to ordinary rusting of .cast iron by tap water, about which more will be said.
To clear the cooling system of all these possible causes of blockage, something more is required than the use of boiling soda water, or even the more drastic method of ',ping caustic soda. It will be found, however, that, used sensibly, either muriatic acid (spirits of salt) or oxalic acid will do a thoroughly satisfactory job. Either may readily be obtained from most chemists.
The procedure is simple. Assuming inuriatic acid be used, then, after draining and flushing the radiator, mix approximately one quart of acid with five gallons of water. It is most important that the acid be added to the water and not vice versa, otherwise the result may be really "atomic."
Use an earthenware crock, an acid or distilled-water carboy being ideal. To avoid splashing, it is advisable to use a glass funnel when pouring the mixture into the radiator. Similarly, take precauticrns against over-filling and allow ample room for expansion of the liquid when hot. The solution is extremely corrosive and should not be brought into contact with clothing or the skin. The mixture should be left in the codling system for from 15 to 20 mins. with the engine running fairly briskly to ensure maximum agitation. When draining off, unscrevi the taps completely to secure maximum unrestricted outlet. Make sure that the mixture is safely collected without it being splashed over the outside of the block or other chassis parts.
Using Washing Soda as a Neutralizer After draining out, .flush with a neutralizer—ordinary washing soda is quite satisfactory—so as to kill all traces of acid. This acid-flush treatment should prove 95 per cent, successful in curing the most obstinate cases of choked cooling systems. It is not a preventive against scale formation, and so far as the writer is aware, nothing has so far been developed that is effective in this direction. Much promising work has been done with chromic-acid mixtures permanently retained in the cooling system, but, apparently, results are not yet conclusive.
Therefore, a periodic acid-flush of the cooling system of any vehicle should be well worth while. The writer is no advocate of these period-overhaul schemes that, before the war, were considered essential — as distinct from normal periodic maintenance work such as greasing, washing and battery topping.
War-time exigencies have shown that, in most cases, it is a waste of time and materials to tear down and overhaul perfectly good assemblies merely because they have reached a certain mileage life. A thorough periodic cleansing of the cooling system, however, although there may be no apparent signs of overheating, is well worth the two to three hours dock delay involved.
• It will pay good dividends by preventing cracked cylinder heads, distorted and burnt valve seats, seized rings and scored pistons. In nine eases Out of 10 it will effect an improvement of from 2 to 5 per cent. in m.p.g.
Many operators will question this last claim, for there is a widespread opinion that most engines are overcooled. Instances are quoted of imjiroved performance when a portion of the radiator is blanked off, or even with the fan removed. Such practices might prove harmless under conditions of light running, or particularly in winter, with the older-type, comparatively low-speed large-capacity engine.
Designing Difficulties That Have to be Met With the modern, relatively smallcapacity high-speed unit, there is very little margin against overheating. The engine designer endeavours to attain several apparently conflicting objectives when aiming for maximum power output and economy. First, to avoid vapour locking, the fuel must be conveyed to the carburetter float chamber and kept there at a temperature as little above 85 degrees F. as possible. Hence the fitting of heat-insulating flange blocks between the carburetter and inlet manifold. Secondly, the inlet manifold must attain, as quickly as possible after starting from cold, a temperature just sufficient to prevent mixture "droplet" formation, or mixture condensation, but not high enough to cause expansion of the gas and loss in volumetric efficiency. The fitting of a thermostatically controlled exhaust manifold to inlet manifold by-pass is the answer.
Then, to secure rapid burning of the mixture in the combustion chamber, and to prevent loss of heat resulting from compression, the temperature of the cooling water in the jacket and cylinder head must be raised as quickly as possible. A thermostat fitted in the outlet hose will look after this. But once warmed up, the qylinder-head temperature must not exceed a point where detoriation would occur, and, as only a portion of the heat generated by combustion of the fuel is converted into useful work, Ow surplus—about 25 per cent, in the case of a petrol engine— must be absorbed by the cooling system as quickly as possible. The rate at which this excess heat is dissipated through the radiator will depend largely on the cleanliness of the entire cooling system. Just as a scaledup kettle will take more fuel to bring its water up to boiling point, :nd will then take much longer to cool off, so will a scaled-up cylinder block take longer to reach an even working temperature, and longer still to dissipate dangerously high temperatures from certain hot -spots.
To carry the simile farther, if the scale on the kettle be particularly thick and the fire concentrated, then a hole might be burnt in the kettle before the water in it had commenced to boil.
All this may appear elenientary, but sometimes the obvious is overlooked. Overheating may take place in an engine although there be no outward or visible signs of boiling. A radiator thermometer is an attractive fitting, but it may prove misleading, because it does not proclaim localized hot spots in the cylinder head and around the exhaustvalve seats. At these points the temperature may reach that of superheated steam, although the radiator water may be well below boiling point.
The designer knows all about these heat pockets and calculates the capacity of the radiator and water pump accordingly, basing his computations on so many square inches of clean, free-fromscale metal surfaces.
This is the answer to those people who claim to have found oil a satisfactory cooling medium, and, in consequence, have used it in frosty weather. Whereas water transfers heat rapidly, not by conduction, but by convection and radiation, oil does so only one quarter as effectively. Oil will not crack a block by freezing, but it may do so by failing to atoll overheating. In addition, overheating of the cylinder head will result in detonation, and even that may not be detected except by an apparent loss in pulling power, lower m.p.g. and a general roughness in the engine that spells trouble at a later date.
Corrosive Effects of Anti-freeze Mixtures
At this period of the year, it is opportune to mention the subject of antifreeze solutions. With the single exception of alcohol mixtures—and these are not very popular because of the need for constant topping-up to take care of loss of strength through evaporation— practically all anti-freeze mixtures will cause corrosion unless treated with satisfactory corrosion inhibitors. Not only will this corrosion result in-damage to surfaces of the water jackets, and particularly aluminium parts, but it will cause, subsequently, considerable choking and blocking of the cooling system.
Pure glycerine is corrosive and so is radiator glycerine—a 60 per cent. concentration of glycerine as used by many makers of anti-freeze mixtures. Ethylene-glycol is similarly corrosive, but anti-freeze mixtures, specially compounded by reputable manufacturers, all contain effective corrosion inhibitors. Usually, the container is plainly marked to this effect.
There are other types of anti-freeze mixture that might be used in an emer
gency, such as those containing magnesium, calcium chloride or common salt, glucose and sugar. etc., but none is really suitable, although they are low in cost. Some of them, particularly calcium chloride and salt, would play havoc with aluminium.
The fact that ordinary mains water causes fairly heavy corrosion is not always realized. The effect is much worse in certain hard-water districts, where it may be found that aluminium cylinder heads and water-jacket side plates practically disintegrate in lass than two years' service. This kind of corrosion, however, is comparatively simple to combat. About 2 ozs. of potassium dichromate for a four-gallon, capacity cooling system will inhibit 95 per cent, of the corrosive effect of mains water, Potassium dichromate may be obtainedfrom any photographic supply chemist for from lid. to 2d. per oz., or from manufacturing chemists for about 2s. per lb. It is easy and safe to use, it being merely necessary to drop one or two lumps into the radiator; it will dissolve very readily. It is permanent in its effect and need be replenished only in proportion to the amount of cooling water lost through leakage. Actually, it will tell-tale leakage points by leaving a bright yellow stain which is quite
harmless and easily removed.
To sum up—keep the cooling system clean by a periodic acid-flush, add potassium dichromate rust inhibitor every time the radiator water is changed. and stick to one brand of recommended anti freeze.