Engine cooling system and Servicing

The engine cooling system is as important as anything else in the engine.  It is a system that has controlled recirculation and flow of a coolant fluid to transfer heat energy from inside the engine into the atmosphere.  This is done by a system of hoses that run to and from the engine into an important component in any engine called a radiator.  The radiator, like an inter-cooler, runs the fluid through very thin paths across radiator, and as air passes through these thin paths, the heat of the fluid is transferred away into the atmosphere.  The coolant is a very important part of the cooling system, it must not freeze, boil, and cause engine parts to corrode.  It is generally made up from two parts water and one part anti-freeze.  Anti-freeze is a liquid made of Ethylene glycol, or in some cases, propylene glycol, and is mixed with corrosion inhibitor to stop corrosion from forming on engine parts.  Most anti-freeze is a very bright green colour, or in some cases can be a pink/red colour, which is an ethylene coolant.  This cooling system is also used by the air conditioning system, and inter-cooler systems for forced inducted petrol engines, and in some cases, turbo diesels.  In motor sport, they use a similar component for cooling oil, which is basically a small radiator which runs oil through it to cool it down.

Here is a small diagram of how the cooling system works.  There is a set of hoses which run from the engine to the radiator.  The hot fluid from the engine runs to the top of the radiator, and as air passes through it while driving (or the insisting fan while stationary), the air cools down the fluid within the radiator. as the cool fluid sinks down,  it then re-enters the engine at the bottom, and so on and so forth.  There is also another heater core which is basically like a radiator inside the cabin of the car, which uses the heat of the fluid to warm the interior. To check if the flow is working properly,  you can feel the top hose of the radiator and if it is hot, then there is flow.  Depending on engine temperature, this will tell you when there is flow when there should or should not be.

Of course, we don't want the cooling system when the engine is not warm.  The re-circulation of the coolant is controlled by a very special and important component called the thermostat.  The thermostat sits at the radiator hose, which shuts when it is cold.  This causes the flow of the coolant to stop.  The thermostat has a wax in it that when coolant is warm enough, the wax softens and therefore opens the thermostat.  This then allows coolant to flow through the engine.  This component sits just behind the hose grommet on one of the radiator hoses. 

This component can be tested easily by boiling some water, dropping the cold thermostat in the hot water and seeing if it opens.  The thermostat not opening or closing can cause major over heating problems or cause the engine to take very long to warm up.

The flow of the coolant is run by a water pump, which is run off either the timing belt or a separate belt.   This means that the pump is running constantly as the engine runs.  When the engine speeds up, the water pump speeds up as well.  Water pumps can come in all different types (especially in the new Toyota engines) but do  basically the same thing.  The water pump is usually changed when the timing belt is changed, for guarantee purposes.  This is because water pumps can leak over time, and water dripping on the timing belt can damage it and cause squeaking sounds. The replacement of the water pump is very easy while the timing belt is removed, simply remove the old one, compare it with the new one and bolt the new one on.  They should of a gasket to go along with it as well.  

Maintaining the cooling system is crucial,  many things can go wrong as a bad cooling system can cause the engine to seize.  A few tests and procedures can be done to make sure the cooling system is healthy. First of all, make sure all the components including the radiator, hoses and the flow is correct.  A dry and cracked hose must be replaced.  Check that there are no leaks anywhere.  We can also do a pressure test to the system by removing the radiator cap, and placing a pressure gauge to it.  This requires the correct adaptors and gauges.  The gauge should also have a pump, so pump it as much as you can and check the gauge.  If the gauge is in the green zone, it is fine.  If the pressure drops quickly, there is a leak somewhere.  You can also check the density levels of the coolant by using a hydrometer.  It is very similar to checking the battery fluid.

Another maintenance procedure is to do a flush of the system.  There is a bleeder bolt near the thermostat that is basically a hole that is below the level of the top of the radiator. That means any air trapped in the system will be bled out.  Remove the coolant by removing the bolt/tap underneath the radiator, and the coolant will pour out.  use a hose and run water through the system for about five minutes.  Make sure when replacing coolant that there is no air in the system.  One small bubble of air can actually cause the coolant to boil and evaporate, losing coolant (especially in turbo charged engines, as they get very hot).  Make sure the mixture is at least two parts water and one part coolant (or according to specification).  The overflow tank will also need some fluid, if the engine is cold, it will need about 1/4- 2/3 of a full tank of fluid.  Run a quick test once all done that when the engine is still warming up, that the top hose is not yet warm.  This means that the thermostat has not yet opened and that flow is only recirculating within the engine and not the radiator.