Cooling Systems

Cooling systems are one of the most neglected systems on a vehicle, yet are so easily maintained by most people with or without any mechanical acumen, they are crucial to the efficient running of a vehicle, fuel economy and emissions.

Cooling systems operate by using water and other chemical systems to cool the engine, and have to dissipate the heat generated, this has to be done in two ways with 4X4 vehicles. Ordinary road going vehicles dissipate heat using the motion of the vehicle as it travels along a road at normal road speeds, the air flows through the radiator to cool the hot water passing through the radiator from the engine. This is known as the ram-air affect, basically the vehicles speed is the speed of the air entering the radiator to cool the water, and is said to be proportional; this is that its air flow is proportional to the vehicles speed. If a vehicle is travelling along a motorway at 70 MPH we know its proportional air is entering the radiator at 70 MPH, we can therefore accurately match the airflow to the vehicles needs and requirements.

4X4 vehicles airflow is non proportional, in simple terms if low range is engaged for off road work the engine revolutions and power output from the flywheel are the same, but the airflow through the radiator is much less due to the slow vehicle speeds. 4X4 vehicles also encounter another problem, their working environment; a road vehicle may pick up normal debris such as insects or normal road rubbish in small quantities, this may affect the cooling capacity but not by a significant amount. 4X4 vehicles may encounter leaves, twigs, and mud; this is more crucial and detrimental to the cooling system as it impedes the airflow through the radiator, therefore 4X4 cooling systems are over capacity, non proportional systems.

How Does It Work

Cooling systems employ the same basic components which are; the engine to produce the heat, the radiator to dissipate the heat, the thermostat to control the engines temperature, and water pump to give the water direction. Cooling systems may also contain a number of other systems such as the heater matrix which is a small internal radiator to heat the vehicles interior, air conditioning or climate control, and a range of systems to heat other components quickly in colder climates.

As the engine is started it develops heat, this is absorbed by the water jacket in the engines cylinder block, this heating water rises to the top of the engine which is the cylinder head, as the cooling water heats up the thermostat opens. Thermostat’s openings are temperature dependent and effectively control the hot waters temperature and flow to the radiator, this is called the thermo-syphon effect as it uses the rising water to circulate it to the radiator. The water pump actually circulates the water in a specified direction, contrary to popular belief it does not actually pump in older vehicles, it just gives direction; on newer vehicles it does have a pumping affect which is not a lot; as the water heats it expands and forms pressure. We now have pressurised hot water controlled by a thermostat moving in a defined direction around the engine, with a proportion of it being released into the radiator for cooling; this is what gives us a consistent engine temperature. Some of the ancillary items such as the heater matrix receives a proportion of this heated or heating water to defrost the vehicle, or warm the vehicles interior.

While the vehicle is moving on road, in high range the vehicle is acting in the proportional manner as it receives airflow at proportional speeds through the radiator. If a vehicle stops suddenly, the normal one being from motorway speeds to stationery; the heat generated is the same but our proportional mode suddenly stops as we still have the heat, but no cooling airflow, and the temperature rises, this is called heat soak. The temperature gauge rises by a proportion, this is normal; the other item we have omitted comes into play, this is the cooling fan which does the job of the ram air effect by pushing or pulling air through the radiator to cool it, then it cools other components as it exits the vehicle. This situation also arises in town or other stop start driving scenarios, but not to the same degree as the engine is generating less power, so less heat to dissipate.
Cooling fans come in three basic sorts, these are the direct driven fan which works all the time, viscous fans which have a temperature controlled element which controls oil flow to operate the fan, and electric fans which operate with a thermo or temperature controlled switch. Viscous and electric fans do not run until they are required, they simply idle until triggered by the engines temperature opening the viscous fans control valve to let the drive oil travel through to drive the fan, or the thermo switch triggering the electric fan. While the vehicle is travelling the fans may appear to be running through the airflow driving them, viscous fans have “another trick” they are temperature controlled, therefore rotate at variable speeds in tune with the engines temperature. Viscous fans always contain a slight amount of oil in their driving “viscous chamber” to lubricate the mechanism, therefore they often travel at very slow speeds at all times; electric fans employ another method, this is two fans with two thermo switches of differing operating temperatures. One, the primary fan, will always operate at the lower temperature setting dictated by the thermo switch, the other, the secondary fan will activate if the engine temperature continues to rise with the primary fan working, such as a motorway stopping situation.
As we can see the best method of driving a fan for off road vehicles is the viscous fan, temperature regulates its speed so it can compensate with providing a variable air flow through the radiator which is beneficial if it is slightly blocked by debris. Viscous fans are the most expensive to manufacture due to their internal components, electric fans are cheap; two electric fans are still far cheaper than one viscous fan, this is why they are used by most vehicle manufacturers for road going vehicles.

Now we have an understanding of the cooling system principles we can appreciate what it does for a vehicle, and understand why a cooling system needs a little maintenance, and perhaps maintain it a little more often.

Maintaining Cooling Systems

Many cooling systems suffer from wear, this is not wear in the wearing components such as the moving water pump or thermostat, and it is from degradation caused by failing to maintain the cooling system. Electrolytic reaction is caused where differing metals come into direct contact and electricity is passing through them, the less noble metal rusts or corrodes, and this is exacerbated in an engines cooling system as it contains many varieties of metal, and other components.
Engines may be made from many materials such as cast iron cylinder heads or cylinder blocks, aluminium heads or blocks, or a combination of a cast iron block with an aluminium head, here we have two metals. If we add into the equation the various engine sensors which could be aluminium, brass, or plastic, then all the rubber components, the aluminium water pump housing, then all the copper or aluminium of the radiator, and the galvanised water connections we have a system rife with potential problems.
The electrolytic reaction works with the less noble metals corroding over time and deposits fall off, these circulate in the cooling system and form lumps as they are attracted to other particles, these then settle in the bottom of the block or radiator. These particles then begin to block the system and inhibit the waters ability to circulate and cool; another factor exacerbates this situation, this is plain water being used in the cooling system, or dirty water from a stream or other dirty source. Plain water allows rust to form internally in the engines cooling system, dirty water allows other contaminants such as mud, dirt, or silt to enter the system; and water in certain areas such as hard water contains contaminants such as limestone which forms scale.
Preventing this internal corrosion is the job of anti freeze, contrary to popular belief its main function is to control and minimise internal corrosion of the cooling system, a secondary function is to prevent freezing of the cooling water in the cooling system. Many owners neglect the cooling system, even the fastidious owner cannot compensate for any neglect from a previous owner, or owners; this is why it is essential to clean and protect the cooling system. Common problems are running without anti freeze, running the incorrect mixture of anti freeze, not changing the anti freeze at its specified intervals, and just topping the cooling system up with plain water, so diluting the anti freeze mixture. One other failure common to so many older vehicles is the lack of any form of cleaning the cooling system periodically which exacerbates the forming of many of the deposits in the engine and radiator.

Cleaning The Cooling System

Cleaning the cooling system is necessary every five years, this assumes that the cooling system is in good condition, and the anti freeze is replaced at the specified intervals as dictated by the anti freeze manufacturer, and of the correct strength.
Before beginning ensure the heat setting for the vehicles internal matrix is set to the hot position, this ensures the control valve is open and the matrix will drain and refill as well as be cleaned, and not form air locks when the system is refilled.

Begin by draining off the engines coolant, do not the drain plug on the radiator as this is tiny and will not let out any larger particles, with a warm; not hot engine, remove the radiator bottom hose, the systems pressure will force a lot of debris out. Remove as many of the smaller coolant pipes as possible and flush through with clean water using a hosepipe, this will give them an initial flush and remove a lot of the loose contamination. Replace the pipes and fill the system slowly using plain water, massage the bottom radiator hose to remove any trapped air as the system is filled, if possible raise the front of the vehicle slightly to help remove the trapped air when filling, but not draining.
Run the vehicle with the radiator cap on and allow the vehicle to warm slightly, run the heater fan to check for warm air from the heater vents, and then go for a good run to fully warm the engine, preferably with a proportion of motorway speed running. This will loosen the remaining loose debris, then, drain the system of the plain water as already mentioned above, repeat this with dirty cooling systems until the drained water is clean, it might take several attempts with really dirty systems.

Refill the system with plain water and a cooling system cleaner, follow the manufacturer’s instructions with the cleaner, and then drain when it has cleaned all the stubborn deposits formed over many years. If cleaner is used in dirty water, it inhibits its cleaning abilities, so flush thoroughly before putting this in; if the system is really bad, use a commercial cooling system cleaner which is available from cooling specialists, USE THIS EXACTLY TO THE INSTRUCTIONS. Commercial cleaners are so effective they can eat through engine blocks or cylinder heads, hence the warning, but if it’s in there it gets removed with this stuff.

Flush the system fully with plain water and fully drain, again remove as many pipes as possible and flush then through with a hose as there are many traps which will not properly drain and hold the cleaner and water in the system. Find the capacity of the cooling system and add half this quantity of concentrated anti freeze and top up the system with water, this will give a 50/50 mix of anti freeze and water. Run the engine to hot and check the heater works and there are no leaks; also remember to do the expansion bottle while you are cleaning and flushing.
While the hosepipe is out it is prudent to back flush the radiator to remove any dirt of insects which have become lodged within the cooling tubes, from inside the engine compartment, simply hose through the radiator towards the front of the vehicle.

Always use concentrated anti freeze, do not use the ready for use types as they are only concentrated types ready mixed with water, water is free so why pay for it.
Always use a 50/50 mixture of anti freeze and water, some manufacturers recommend lesser mixtures but these do not give adequate or effective corrosion protection, they simply prevent freezing at much lower concentrations.
Replace the traditional anti freeze based coolants every two years as this is specified by all the reputable manufacturers as the recommended replacement periods for its maximum corrosion inhibition qualities to remain effective.
Newer long life anti freeze mixtures are available, and dropping in price; if these are used the replacement period is extended from two years to four, or five years; so these are beneficial if used at the 50/50 mixture to save replacement every two years.
Any remaining anti freeze can be stored in a container and mixed with an equal quantity of water for topping up, this ensures the systems anti freeze is not diluted and becomes less effective in corrosion inhibition.

Some people ask if anything else should be added, my answer is yes; I always add a radiator sealant, and only use Bars, Bars contains a lubricant which coats the inside of the cooling system and moving components such as water pumps and thermostats. I have tried many other products and found many do not work, and those that do are nowhere as effective as Bars. Add this to the nearly full system while it is being filled, shake the bottle well and just tip in, half fill the bottle with water, shake vigorously again and tip it in, run the engine to circulate everything and fully mix it.

It takes time to clean the cooling system properly, but it is time worth spending so periodically to ensure all is well in the cooling system, what’s half a day every couple of years, or even five years; nothing, so no reason to neglect the cooling system.