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Cooling
Systems and Calcium Deposits; the non-animal Fur (Part
1) by John Whetton
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The "furring up" or lime-scaling of the internal cavities of a car's cooling system, particularly those in older cars 'deprived' of a sealed or pressurised radiator presents us with a severe chemical headache. It eventually leads to inefficient transfer of heat from the block and cylinder head to the circulating water coolant on the one hand and the transfer from the radiator core and the atmosphere on the other. Unless prevented or remedied, severe overheating, partial or complete occlusion of the fine and less fine waterways is an inevitability and finally a choking of the rather more cavernous chambers within the block. Similarly, the radiator core with its fine passages will become the victim of the process. The poor heat conduction from the heat source, i.e. the cylinders will create enormous metal expansion stresses capable of causing distortion and cracking within the block and cylinder head, especially where the expansion rates are significantly different between closely associated regions. The
location of the water pump in relation to the far end of the engine
on the one hand and its closeness of the radiator on the other adds
to the problem. The further away from the pump and the more convoluted
the waterways the greater the resistance to flow which undoubtedly
adds to the precipitation rate of lime-scale in that the reduced
flow induces higher water temperatures. The least resistance to
flow exists between water pump and radiator header tank via the
proximal front cylinders. In this respect the rear part of the block
and cylinder head are most vulnerable to lime-scaling and therefore
cracking. Furthermore, the fine waterway tubes crossing the interior
of the engine offer far greater resistance to flow and on account
of their narrowness have an even further susceptibility to furring-up
and complete occlusion with dire consequences.
Decades of neglect, ignorance and indifference to the needs of the cooling system is often a story of combined lime-scaling and the generation of large quantities of iron oxide, often in scale form or in chunks. The breaking away of these micro-asteroids from the water channel walls will lead to similar sizes of calcium carbonate falling away and both types will now be either in free fall to the lower floors of the water jacket or in circulation in the system. Interference with the water pump is probable and the pump will help to pulverise some of the stuff. In all, we have a mess which, on the one hand will form a well knitted collection of rust and lime-scale, thanks to engine vibration acting rather like a builder's vibrating machine for consolidating hardcore prior to top surfacing. On the other, a 'sandstorm' of finer material destined to contribute to the occlusion process. With lime-scaling of the radiator core and the descent of merely the fine, suspended solids from the header tank downwards, when the engine has been stationary for a few hours or more, one can envisage the potential for a blocked radiator in these circumstances. Back-flushing might offer some short to medium-term relief here. I do not wish to enter cardiovascular discussion here but when our coronary arteries within and surrounding our heart muscle develop an analogous partial or complete occlusion, a heart attack and even death become high risk possibilities. Thankfully, a dead engine block and cylinder head are relatively minor curses. Prevention is better than cure. Repairs to blocks and heads are not just expensive but also not necessarily successful. Replacement may be the only reliable, but extremely expensive, option. The removal of the offending solids from the cavities and fine passages of undamaged blocks and heads will be very, very time consuming indeed. It may be convenient to turn a blind eye to the problem, but the matter can only get worse if you choose to use the car as it should be on a regular basis. A vicious circle of overheating, accelerated deposition of lime-scale, further occlusion of water pathways followed by a worsening overheating problem, will prevail and with potentially catastrophic consequences. Exacerbating the matter will be the reduced efficiency of the radiator; poor conduction of heat to the atmosphere and therefore rising core temperatures in the engine. The "furring" process has all to do with dissolved chemicals in the water we introduce into the system and the changes that occur within the water as a result of increases in coolant temperature and the inevitable loss of pure water as it evaporates freely in the header tank and in the vapour state travels down the overflow pipe. The problem will be exacerbated if the coolant is allowed, or has a tendency to, boil. Putting our problem into perspective is important, I have to say. Whereas in our cars it may take years or even decades to become a significant problem in the almost closed system, just think of steam engines and the grand era of the steam locomotive, where an open system of massive steam production on an hourly basis is there to drive the wheels and huge masses of rolling stock. For the steam engine, the daily accumulation of lime-scale deposits had a severe impact on the maintenance programme and a need for substantial preventative measures by treating the water supply with chemicals before the tanks are filled, particularly where the water feed was predominantly from a hard water source. A lack of de-scaling and/or preventative measures had a dire effect on engine performance and deterioration. So, what constitutes the offending 'devil in the water' that can cause so much misery, damage and expense? It is all to do with the inclusion in our water supplies of dissolved calcium salts and to a lesser extent magnesium salts, more specifically calcium bicarbonate and the sulphates of calcium and magnesium. None of them highly soluble in water and very happy to be participants in either a simple chemical conversion in which calcium carbonate is precipitated or, as in the case of the two sulphates, a simple physical change from the dissolved or ionised state into the reconstituted or solid form. The result is a whitish mixture of solids collectively regarded as 'scale', 'lime-scale' or 'fur'. The water supplying agencies do not introduce these calcium salts by intent during the purification process. They enter the water by a natural chemical process after the rain hits land and during its passage to the reservoirs, wells and springs, through soil and in particular through porous limestone rocks and deep chalk deposits. Limestone rock, chalk deposits and the soil arising from them contain the calcium carbonate that ends up as the lime-scale in our cooling systems, our kettles, our house hot water systems, our central heating radiators and pipes, as well as on the external orifices of our showerheads and taps or faucets. Victims of geographical location. If your home water supply has never passed through rocks or substrata or along riverbeds containing calcium carbonate, you will be lucky, though perhaps somewhat unlucky from a physiological point of view because our bodies do need some of the water-born calcium and magnesium. People on very severe slimming regimes, often deficient in essential minerals, hard water might be a life supporting nutrient. However, normally speaking, for those whose water supplies are not from a limestone/chalk source, lime-scale will be alien to their households, their hair will shampoo well (never a 'bad hair day') and purchases of soap, shampoo and other detergents, not to mention de-scaling agents for the sinks, toilets and baths will be minimal. Their guests are less likely to be confronted by dull wine glasses on the dinner table either. Their cars will be lucky too. Such households are being supplied with 'soft' water. On the other hand, a supply of water that has passed through acid soils and has then permeated substantial limestone or chalk deposits will be saturated with these calcium and magnesium salts and they will be the geographical/geological victim of 'hard' water with all the consequences of lime-scaling. The softness/hardness factor is not an all or nothing situation and it all depends on the Total Dissolved Solids (TDS) of the water concerned, varying from 'Soft' with 0-17 gms per litre of calcium carbonate equivalent, through 'Slightly Hard', 'Moderately Hard', 'Hard' to 'Very Hard' with more than 180 gms per litre calcium carbonate equivalent (USA Water Quality Assurance Ass'n). The harder the water, the greater the problem for us as consumers and the more severe the consequences in a variety of directions not excluding the cooling systems of our older cars. The wider perspective. I remember as a small boy, during long walks with my father across fields on the Nottinghamshire/Derbyshire border, being made aware of some of nature's wonders including the investigation of the contents of the small streams in ditches. It was fascinating to pick up petrified leaves and twigs from the previous autumn. The same calcium deposition process prevailed here; elevated temperatures from solar radiation and a little bit of water evaporation causing the precipitation of the calcium carbonate over the surfaces of the dead vegetable matter. It is possible that any alkalinity from the soil in the surrounding fields would have added to the potential for precipitation. In all, the leaves were an attractive sight, seemingly trapped and preserved in shape, if nothing else, in incredible detail. In some regions of the world, entire sunken forests of trees have thus been petrified. Lime-scaling's most glorious manifestation of course has to be the formation of stalactites and stalagmites in limestone caves. These are the result of the same shift in chemical equilibrium we identify for petrification and the deposition in our cooling systems, kettles etc. The calcium bicarbonate-laden solution drips from the roof of a cave over a period of thousands of years, warmed slightly by the air currents and subject to the evaporative process. The outcome is one of nature's most beautiful creations imaginable; the shapes, texture and variability of colour due to impurities such as iron oxide enhance what would be in other circumstances a fairly mundane process of crystal formation. I am also reminded of lime-scaling when I have my regular dental inspections. The calcium carbonate precipitation is easily identified by the dentist on the teeth and one might be able to feel its roughness by tongue touch. This deposit, however, is little to do with evaporating hard water, more to do with calcium bicarbonate in the saliva, there to maintain a slightly alkaline environment for the optimal working of the salivary enzyme, ptyalin or salivary amylase, which commences the digestive breakdown of starch. Since the saliva tends to run downwards in the mouth cavity on account of gravity, the lower teeth, especially those at the front, are far more likely to be victims of the lime-scaling, where evaporation of the saliva when the mouth is open accelerates the process. Those who talk incessantly and those who are mouth breathers are more prone in this respect. Rainwater: more harmful than you think. The other factor is rain water. As the water vapour in the atmosphere condenses (way up in the stratosphere it will be as ice crystals) it will at first be more or less as pure as it gets, but during its descent as raindrops, atmospheric carbon dioxide, although representing about 0.34% of air, readily dissolves in it and since the water is just above freezing pint initially, the rate of dissolving is at its highest. The result here is the creation of carbonic acid. The other gases in the air, mainly nitrogen and oxygen, add to the watery concoction we think of as the pure and wonderful stuff hitting the land and our umbrellas. Pollutants such as sulphur dioxide coming from the burning of fossil fuels, including the fuel we use in our cars, are part of this addition. The formation of carbonic acid:
The reaction between carbonic acid and limestone or chalk:
The CO2 will tend to leave the solution to enter the surrounding air as gaseous CO2, especially when the mixture is heated up. Incidentally, the difference in acidity between pure water and rain water is sufficient to kill our body cells. Fortunately, we have inbuilt chemical mechanisms to contain this threat. Whereas the carbon dioxide (CO2) in solution forms carbonic acid, the sulphur dioxide (SO2) forms sulphuric acid, albeit in a very dilute but nevertheless corrosive form. Both of these are responsible chemical agents in the dissolving of the solid calcium carbonate to form calcium bicarbonate and calcium sulphate and as with the formation of carbonic acid in raindrops, the process is temperature dependant; the lower the temperature, the faster it dissolves and vice versa. The problem we have, however, is that there exists a fine chemical equilibrium between all partners in the chain and the ambient conditions. Heating up the solution drives off dissolved carbon dioxide (as well as all other gases in air) which leaves chemical 'room' for more dissolved carbon dioxide, the source of which has to be the remaining carbonic acid. The chain of reactions here dictate that as the latter leaves the system, the calcium bicarbonate is obliged to convert to the calcium carbonate from which it began its 'life'. Precipitation of this solid is the inevitable outcome and this is how the scaly mess we find in all of the places and cavities mentioned earlier gets there. Non-reversibility prevails. One might think that when the water later cools down, the chemical process will be reversed. If only! If the air space, if it exists above the surface of the water, were to be highly voluminous and it contains CO2 and SO2 etc, there is an opportunity, but the surface area for the diffusion of these gases into the water is incredibly small and the process therefore incredibly slow; too slow for any effect to be felt deep down in the cooling system. The matter is worsened by the fact that the cooling systems in older cars are not closed, but open to the atmosphere by way of the overflow pipe and to some degree via the radiator cap. Even when left standing for weeks at a time the water in the header tank is going to engage in evaporation and of course when the car is being used, from the hotter water, sometimes close to or at boiling point, the evaporative losses are significant. The consequence of these losses is a knock-on effect to the chemical equilibrium mentioned earlier. Since the solution of calcium bicarbonate will be as saturated as it can be under the very watery conditions in which it was formed initially ie the movement of rainwater through limestone rock, if the water is partially removed from the solution in the cooling system, the amount of bicarbonate must be reduced and therefore lime-scale will be deposited on the metallic surfaces. Thus, the heating of the solution and the evaporation of the water join forces to play havoc with our engines. What
is the solution?
Zeolite is really Sodium Aluminium Silicate, a rigid 3-dimensional crystalline compound with well defined internal pathways which facilitate a good internal flow of water through it. In contact with calcium bicarbonate, it causes the calcium ion to bind, forming calcium aluminium silicate and leaving the sodium ion as a relatively harmless contaminant in the water. The product of this non-precipitating process has no increase in alkalinity and is therefore less injurious to the iron and aluminium of the block and head. The Zeolite, normally sold in bead form, will need rejuvenating from time to time by flushing out using a solution of common salt (NaCl) or brine. The sodium displaces the calcium and magnesium from the beads which is then disposed of as carbonates into your kitchen or garage waste pipes. The harder the water, the more frequently the refreshing of the compound needs to be done. 2)
Use nothing but distilled water for a complete fill-up or the regular
top-up. 3) Changing the cooling system water on a regular basis with more of the same hard water or even a newly found source of softer water will not reduce the scaling already present. In this respect, what is done is done. Using very soft water will arrest the problem at best or slow it down at worst. Don't forget to replace the anti-freeze. 4) Even if your water supply is as soft as it can get, it will still contain minerals. If your practice is to top-up the water levels without ever changing it, the mineral content will become more concentrated with time (years rather than months) and inevitably this will lead to some precipitation at some point. Replacing the water every year or two ought to become routine despite the cost of replacing any corrosion inhibitors or antifreeze. 5) The introduction of a corrosion inhibitor to the coolant is important. Where climatic conditions dictate a close to freezing environment (do not forget the harshness of wind-chill), an antifreeze compound is imperative. This will not only do the obvious but if it is the correct stuff, will act as an inhibitor. Ethylene or propylene glycol, as antifreeze, will inhibit corrosion of the metals of the block and head, but they will not inhibit the laying down of lime-scale. 6) If you live in a hard water area, move house. Conclusion. The use of distilled water in conjunction with a corrosion inhibitor/antifreeze is probably the best preventative measure for lime-scaling and internal corrosion. The alternatives may provide some small degree of protection at best and a slippery slope to a very expensive catastrophe at worst.
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