Cooling system


  • General
  • Consequences of too much or too little cooling
  • Different ways of cooling
  • Liquid cooling
  • Pressure test

It is important to cool the engine, as the engine can overheat, compromise lubrication and are most likely to cause knocking (uncontrolled combustion). The thermal load on the motor also has a great influence on the service life. Both the engine oil and the coolant have the job of cooling the engine internally. An engine's cooling system contains a number of very important parts that are listed below:

  • Expansion reservoir; A stock of coolant is stored here
  • Heater radiator; for the interior heating
  • Thermostat; 2 pieces, divided over 2 cooling circuits
  • Radiator; The coolant is cooled here by the passing air (driving wind)
  • waterpomp; ensures the circulation of the coolant. The water pump is usually driven by the timing belt or multi-belt. Nowadays, the water pump is also increasingly driven electronically.
  • parking heater; preheating the coolant before starting the engine. This is often an option. Most cars are not equipped with a parking heater.

De cooling fan protects the cooling system from overheating.

Consequences of too much or too little cooling:
A lack of cooling can be caused by the fact that the coolant cannot circulate properly. This can be due to the presence of too little coolant (leakage), a blockage in the cooling system (e.g. the radiator), the water pump is defective and the coolant no longer circulates properly, or when the cooling fan / visco fan does not turn on. The following things can happen as a result of insufficient cooling:

  • Overheating;
  • Seizing of engine parts;
  • break piston rings;
  • Thickening the engine oil. (Lighter components evaporate in the oil making it thicker);
  • ping.
If gasoline engines overheat, they can ping. The fuel then ignites too early, even before the spark plug sparks. The compression pressure and compression temperature become so high that the mixture ignites on its own. Large temperature and pressure differences arise locally in the combustion chamber. This can cause a lot of damage to engine parts.
Knocking can also be caused by petrol with too low an octane number, an air/fuel mixture that is too lean, an ignition timing set too early or carbon deposits in the combustion chambers. More information about this can be found on the page ping.
Also, the engine can be cooled too much. The temperatures then remain too low, so that the operating temperature is not reached. This could be because, for example, the
  • High fuel consumption (the engine does not reach operating temperature).
  • Internal contamination (at low temperatures, more combustion residues and dirt particles remain in the engine).
  • Condensation of fuel particles (poor combustion).
  • Stove in the interior does not heat up.

Different ways of cooling:

  • Indirect cooling: The warm air is coolant absorbed and then delivered to the wind in the radiator. That is why liquid cooling is called “indirect cooling”. Today, all passenger cars have indirect cooling.
  • Direct cooling: The heat is eventually dissipated by the driving wind. Because the heat is released to the outside air during air cooling, we speak of direct cooling. Older cars were often air-cooled (eg the first VW Transporters and Beetles). By applying cooling fins on the engine block, the parts were cooled by the driving wind. Wind cooling is a simple and cheap way of cooling. The wind flows past the cylinder and absorbs the heat directly.
  • Forced air cooling: A fan blows cool air past the cylinders and cylinder heads. Cylinders and cylinder heads are also equipped with cooling fins. By means of plating around the fan and the parts to be cooled, the cooling air is distributed in such a way that an even cooling is achieved.
    The advantages of air cooling include that less maintenance is required. There can be no leakage as with liquid cooling, the liquid level does not have to be checked or replaced, etc. There is also a shorter warm-up period. The coolant does not have to be warmed up before starting, so an engine with air cooling is faster at operating temperature. This also reduces wear during the warm-up period.

Pressure test:
If the coolant level in the reservoir continues to drop, there is likely a leak. Sometimes the leakage is so minimal that it is not perceptible when looking at the engine block and the surrounding components with a flashlight. The small amount of coolant that ends up on a warm part of the engine, for example, can evaporate, so that no leaks are left behind.
Because the cooling system is depressurized when the engine is switched off (cold), there will be no leakage of coolant during standstill. In such cases, the vehicle's cooling system may be pressurized. The coolant can leak through places where a gasket is dried or cracked.

An example of the pressure test is shown in the figure.

A pressure tester (often a hand pump with a dial gauge indicating the pressure) comes with a number of different mounting caps. Not every coolant reservoir or radiator cap connection is the same. After mounting the correct pressure cap, the pressure tester can be connected to the cap with a quick coupling. By moving the piston rod of the pressure tester back and forth a number of times, an overpressure is placed on the cooling system. The radiator hoses and cooling hoses on the engine will harden. It is sometimes necessary to pressurize the cooling system for at least an hour before a leak is visible. Drops can then form at the ends of hoses, gaskets of the thermostat housing or other coolant covers.

The illustration shows a leak at the lower radiator hose:

When a leak is discovered, it must be remedied with new parts. Sometimes a new gasket or O-ring of a few Euros is sufficient. Do not under any circumstances throw sealant into the radiator. This so-called “radiator stop leak” can cause blockages in the cooling system. This not only closes the opening where the leak is located, but possibly also the cooling channels in the radiator or heater radiator.

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