| A vehicle engine converts less than half of the chemical energy in fuel to mechanical energy that moves the vehicle forward.
The balance is converted into heat. Temperatures in the engine’s combustion chamber can reach up to 2,500 degrees Celsius.
Some of this heat goes out the exhaust pipe, but most soaks into the engine, increasing its temperature, and by association also heats up the environment in which the vehicle’s driver operates. An optimally functioning cooling system for the engine is a must, but modern drivers increasingly see an air conditioning system for the cabin as a must, too. Both systems however need regular care and maintenance.
Cooling the engine
On the one hand, an engine runs best at a fairly high temperature, generally about 93 degrees Celsius. At this temperature, the combustion chamber is hot enough to optimally burn fuel, which reduces emissions. In addition, engine oil becomes thinner, which allows engine parts to move around more freely, which reduces their energy use and wear and tear.
On the other hand, if enough of the heat does not dissipate, the engine metal will get hot enough for the pistons to weld themselves to the cylinders, which usually means the complete destruction of the engine.
The job of the cooling system is therefore to allow an engine to heat up to its optimal level as fast as possible, and then to keep the temperature at that level. It does this by using a centrifugal pump, driven by a belt connected to the crankshaft of the engine, to circulate a coolant through the engine block. There, the coolant absorbs excess heat.
The system then pumps the heated coolant via the cylinder head, which contains a thermostat, through hose to a radiator. There it runs through a multitude of metal fins exposed to air flow created by both the vehicle’s movement through space and the engine fan. The coolant’s heat transfer to the radiator’s metal, which transfers the heat to the air. The cooled-down coolant then goes to the engine block again. If the engine needs to become hotter, the plumbing around the thermostat redirects the coolant to the pump directly, rather than to the heat exchanger.
The vehicle’s cooling system needs seasonal checkups to prevent premature engine wear due to extreme climate fluctuations, checkups during routine servicing, and a dedicated service at least every two years.
The integrity of the coolant is crucial for the correct functioning of the cooling system. The coolant must be a consistent mix of equal parts water and ethylene glycol to enable it to resist freezing or boiling, given the variety of temperatures to which the engine gets exposed. The system is under pressure and must remain so, to further maintain the coolant’s boiling point at a high level. The coolant must also consistently contain the correct level of corrosion inhibitors to protect metals from corroding and prevent cavitation erosion in water pumps and wet liners.
Good maintenance practice indicates an engine’s cooling system must be checked regularly. Non extended life coolant must be drained, and the system flushed and refilled with coolant at least every two years.
This biennial flushing is necessary because a conventional drain and refill service could leave as much as half the old coolant in the system, as only free flowing coolant will drain from the radiator. Coolant deteriorates over time and from scale deposits and acidic by-products. Cooling passages can get build up of scale and sludge and coolant will not flow freely enough. This could compromise the coolant’s ability to absorb and transfer heat.
Auto technicians must also take care never to cross use extended life and standard coolant, and to ensure there are no air pockets in the system after servicing the cooling system.
Leaks in the system can seriously compromise the coolant’s integrity, too. The coolant levels can go too low, as can the pressure. Parts to check for leaks are the heater core, water pump, thermostat housing, head gasket, freeze plugs, automatic transmission oil cooler, cylinder heads and block, and the possibility of wear in hoses, gaskets, clamps, and radiator clamps. In many instances parts such as radiator hoses wear from the inside out, so checks need to be thorough. The oil dipstick can be checked for evidence of coolant, which if present will show as easy to spot droplets or sludge, and could indicate internal leaks.
With their huge fin areas, radiators are vulnerable to leaks and internal and external clogging, and consequently need careful checking and cleaning. They are exposed to stress vibration, so the radiator mounting needs careful scrutiny. Radiators age well, but may need replacement in older vehicles that have seen hard use.
The technician must check, with the engine hot, to ensure the cooling fan comes on at the correct temperature and operate properly. They must visually inspect drive belts for glazing or deterioration, and check this against the vehicle manufacturer’s specs for the right belt size, tension and deflection. Finally, a functional testing of the heater unit can give a good indication of the cooling system’s status.