Cooling Systems

Cooling systems are used when the need arises to reduce temperature of an engine or other devices that are operated by a prime mover. Operating a device or prime mover causes heat to build up and for that reason cooling needs to reduce operating temperatures.


There are air cooled engines (prime movers) and there are water or liquid cooled engines.


For example a small engine that has no radiator just a fan that blows air over cooling fins. If the fan were to stop the engine would also stop after the heat built up to a point of engine failure. A Harley Davidson motorcycle engine is one example of an air cooled engine without a fan. It requires moving to cool the engine as the radial piston airplane engine like in the old crop dusters. Those engines both the Harley and the crop duster engines are the mechanics choice. The engine is designed extremely well by needing less components to cool the engine. Radiators break, hoses rupture, water pumps fail and the list goes on. There are some setbacks to not needing a water cooling system but the benefits are longer lasting engines requiring no cooling system repairs.



Prime movers with water cooling systems require something to contain fluid, a tank which is called a radiator because it allows heat to radiate off of it. Then something to cause the water to flow and circulate through the engine called a water pump. Then hoses are needed to allow the water or cooling fluid to go through a system, from the coolant tank to the prime mover and through back to the radiator.

Antifreeze / Coolant is needed to lubricate the water pump shaft seal and inhibit corrosion inside the cooling system passages. Obviously it prevents water from freezing inside your engine and it is also a coolant that adds cooling ability to the water. The coolant breaks water surface tension and allows it to contact more of the engine cooling passages. They are sand cast and rough, when water is flowing around inside the engine block the coolant allows the water the ability to flow into the areas of roughness. Below is a link to You Tube video regarding a waterless coolant, much safer not poison like the glycol coolants.






The cooling system on the right is a reference to exhibit how the water and coolant flows within the cooling system. The red is to indicate hot coolant and the blue is to indicate the cooler coolant. As the engine is started the water pump is rotated and sucks water from the radiator and bottom radiator hose into the inlet of the water pump. From that point the water is made to flow as the water pump shaft rotates with the engine into the engine block (lower half). After the engine block is filled the coolant then is forced into the engine head coolant passages and is partially blocked by the thermostat valve. As the coolant heats up to the temperature stamped in the copper cylinder face of the thermostat (145 up to 200F) the thermostat valve begins to open and allow the heated coolant to flow into the upper hose of the radiator. A vertical core radiator allows the hot water to flow down the vertical cores which are simply tubes and the flat looking thin plates are called cooling fins. The coolant temperature is reduced when it sinks to the bottom of the radiator and is again caused to flow through the system as described. 

Vertical Core Radiator -- Horizontal Core ------- Core Tubes



The vertical core radiator allows hot coolant to flow into the top hose inlet fitting and flow downward into the bottom tank, the tanks that have the hose fittings are on the top and the bottom of the radiator as it sets in the equipment.


The horizontal core radiator allows hot coolant to flow into the top hose inlet fitting and fill the tank on the left side in this example and then through the horizontally positioned core tubes in relation to how it sets in the equipment. The hotter water is caused to flow toward the right side into the tank on the right side of the cores as it cools into the tank with the hose fitting on the bottom of the radiator.

The core tubes are different in all three examples of the core. The two on the right are called two row cores and that determines how much you system cools the coolant down to. A one row is a cheaper radiator and cools less water than the two, three, four core types. Critical dimensions when replacing the radiator; rectangular dimensions, vertical core or horizontal core, thickness or number of core rows, the size of the fittings that attach the rubber hoses (upper & lower), and location of upper and lower hose fitting relative to the way the radiator sets in the equipment. Note this is from the operators view from setting in the operators seat.  

Water Pump ------------- Thermostat ------------ Coolant Flow --------



The water pump impeller causes coolant to flow while rotating the hub that is pressed onto the water pump shaft going through a bearing and seal. The coolant lubricates the rubber seal lip that seals water from coming to the outside of the water pump. Without coolant that lip will wear out quickly and the water pump will need replaced. There is usually a hole called a weep hole that allows a person to see when the seal is worn out. By operating the engine with the weep hole leaking will damage the water pump bearings and finally break.



The thermostat charge cylinder has the temperature stamped into the bottom face. It is up to the individual to select a temperature and as an experienced mechanic I do not like running a thermostat stamped over 180F. A large gasoline engine should run a head temperature of no more than 170F. The newer vehicles run right at boiling and average 195 or hotter. That is not needed for here and causes great stress on all components of the cooling system.



The thermostat valve will remain closed until the coolant reaches the temperature stamped into the face of the cylinder.

Fan clutches are designed to monitor engine temperature and allow the fan to slip when the temperature is low and as the temperature rises the fan clutch locks the fan to the shaft and is rotated at a one to one ratio along with the water pump shaft speed.



The fan clutches if not checked on a regular basis will allow the equipment coolant temperature to rise and overheat by allowing the engine cooling fan to slip instead of locking it up. When a cooling fan clutch is locked up your engine is hot and you can hear the fan running over the engine noise. It takes more horsepower (more fuel) to run a locked up fan than it does when it slips. In stop and go traffic the engine will overheat quickly if one of these fan clutches does not lock up.

The radiator cap gasket is to seal coolant inside your radiator and cooling system when there are no leaks to the outside or inside of the engine. This allows pressure to build up inside the cooling system and when the pressure reaches the specified pressure in pounds within the cooling system the gasket is pushed up and off it's sealing seat on the radiator and goes into the overflow container and the seal is to prevent the coolant from going outside the radiator through the top of the cap.

Coolant boils at around 212F without pressure, every pound of pressure in the cooling system will allow the water to get hotter by a couple degrees before it boils. Once water boils in a cooling system noises are made and the engine becomes very hot and needs to be shut off.



If you need to replace your radiator cap measure the distance from the radiator cap seal to the face of the gasket. I have seen quite a few engine overheating problems because the cap pressure spring shaft length is not the correct length. For example a Toyota original cap is different distance between the seal and the gasket surface than the replacement radiator cap neck fitting has. Make sure you purchase the correct cap, many sizes fit the same neck but important is the neck depth to the gasket sealing surface.

Tip's from the mechanic regarding cooling system issues.



1) If your cooling system is filled with coolant and there is no coolant loss but your engine heats up very quickly after start up the thermostat valve may not be opening properly. Start the engine and hold on to the top radiator hose and note how long it takes to feel the heat in the hose. If the thermostat has failed to open the hose will not get hot until after the engine overheats.



A temporary remedy is to go to the thermostat housing, remove the bolts and the thermostat. Assemble and then see if the problem is gone. Engines are designed to run at a temperature that allows maximum fuel efficiency. When removing a thermostat remember that the water flow is not regulated and flows as much as it can. Higher engine RPM means higher water flow inside the cooling system. This can overheat the engine because the water flows faster through the radiator not allowing the radiator to cool the coolant as much. I wouldn't worry about  overheating unless I was going high speed through a desert. Remove the thermostat anyway and you will tell immediately if you have found your problem.

2) If coolant is leaking to the outside of the radiator remove the gasket from the radiator cap to eliminate pressure from building up in the cooling system. 

Below link is a You Tube video that demonstrates a cooling system.

You Tube video showing cooling system operation.