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Past Issues
September 1999

Cooling - the Flip Side of Friction

While a lot of attention is paid to aspects such as lubrication as an input into the wear and tear of an engine, an area that has been generally ignored is that of cooling systems and this despite the fact that a poorly maintained cooling system promotes slow destruction of an engine without the operator being aware of the problem. Dave Scott, technical correspondent for FleetWatch, finds it an irony that while the debate rages on whether to use synthetic or standard mineral oil lubricants, slow engine destruction is happening on the coolant side of the cylinder wall. He urges operators to arrest this destruction now!

Be honest. As an operator, do you have in place a cooling system policy and procedures for your truck fleet? If not, may I put it forward that you are ignoring a vital area of your operation for, with turbocharged and intercooled diesel engines becoming a standard feature of trucking, even more strain is being placed on cooling systems to function without letting cylinder liners fail through cavitation arising from electrolysis and corrosion.

It’s not cool to be too cool

It is interesting to note that while truck drivers are warned to watch for signals of overheating, few report the equally damaging converse of over-cooling. The temperature gauge has to be monitored for maintaining a steady rating - an engine that runs too cool will experience the following problems:

  • Condensation takes place in the cylinder and promotes acid formation.
  • Lubrication starts to sludge.
  • Oil consumption increases - lubricants do not operate at the correct temperature.
  • Inadequate combustion leads to loss of power.
  • Wear rate increases of up to 80% can occur.

High pressure is cool

Modern cooling systems work best at high pressure - the object of pressure being to force the coolant against the cylinder wall. Maintaining the recommended cooling system pressure has many benefits that impact on engine life. To mention a few:

The temperature at which water boils is raised.

Water has the unique quality of expanding not only when it’s boils but also when it freezes. For every 0,5 kg increase in pressure on the coolant, the boiling point is raised by 2 0C. A 0,9 bar cap has the effect of raising the boiling point from 100 0C at sea level to 136 0C.

Water pump efficiency is increased.

Pressure introduced on the inlet side of the water pump forces coolant against the water pump impeller, preventing cavitation. An additional benefit is that the capacity of the pump is increased.

The rate of cooling is increased.

The larger the difference between a hot and cold body, the quicker the rate of heat loss of the hot body. Pressurised systems run at higher temperatures and also cool more rapidly.

Steam layers are eliminated.

Steam is a bad conductor of heat and has to be removed from cooling systems. The only way to eliminate steam layers in an engine is to force the coolant against the cylinder wall to carry away the heat. Overheating spots, that are caused by steam on cylinder walls, are not evident on the engine temperature gauge.

The pitting of wet sleeve cylinder liners is eliminated.

Pressurised cooling systems prevent the formation of air bubbles in the water pump. Tiny air bubbles that burst against the cylinder liner cause corrosion. Pitting of cylinder liners is caused to the extent of 40% by cavitation and 60% by electrolysis that results from acidic water.

Pressurised cooling systems prolong radiator hose life.

Air bubbles that enter un-pressurised cooling systems burst against any object that causes a change in the directional flow of the coolant. There are always bends in radiator hoses as it presents an obstacle to be damaged. In cooling systems that are not pressurised, the cavitation bubbles cause erosion of the elbows in hoses.

It’s cool to use only PH7 water

When I observing the topping up of engines, it seems the quality of the water does not seem to matter. Borehole water or river water - anything goes so long as it is wet. You should remember, however, that the property hardness of water is a determining factor in the effects of additives in cooling systems.

  • Water with a PH factor of 3 is classed as soft water or acidic. This leads to rust formation, pitting in water jackets and the promotion of chemical reactions between various metals.

  • Water with a PH factor of 11 is classed as hard water or alkaline. This leads to the formation of scale, retardation of cooling, the blocking of tubes and passages and creates hot spots in the engine.

  • A PH rating of 6,8 to 7,2 is regarded as ideal. This is neutral water.

Note that if additives have to be added to neutralise the water, you must ensure that any additive does not clash with the additives in the anti-freeze mixture. Chemical reactions between additives may cause damage to cooling systems.

Simple issues make a difference

There are many other components of modern cooling systems that will be part of the checks and balances in maintenance procedures. Thermostats, pulleys, pumps and fans all go to make up the system. However, paying attention to the simplest issues only will make a major difference to the efficiency of taking out the heat in an engine and prevent it’s slow destruction. These are:

  1. Write a Cooling System Policy

  2. Train maintenance staff and drivers in the interpretation of the policy and correct procedures. It is not just a process of filling with any water available. Defect reports must cover cooling systems on a daily basis.

  3. See to it that neutral water is used with the best anti-freeze additive in the correct pre-mixed ratios for topping up. Ensure that the entire coolant system is changed at a maximum interval of two years or 6 000 engine hours.

  4. Regularly check that cooling system pressures match - and maintain - the OEM specifications.

Acknowledgements and reference sources

  1. Dupie du Plessis - National Training Manager - Toyota SA Trucks
  2. Toyota SA - ‘Cooling System’ training material
  3. Cummins Service Bulletin - No. 3666132
  4. Shell SA - Product Information - Shell TRIGUARD

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