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Today we're talking about engine cooling and we will be comparing the benefits and drawbacks of air cooled, oil cooled and water cooled engines.
Why do engines even need to be cooled? To answer that question all you have to do is put your palms together and run them quickly. Feeling the heat? Well that heat is a result of friction and there's plenty of friction happening inside an engine, but by far the major source of friction, often accounting to around 40% of the total friction is the sliding of the piston rings against the cylinder bore.
So how do we control the heat? Well the simplest and earliest answer is to use the air already available everywhere around the engine. This means that air cooled engines don't need any additional liquids, liquid containers, hoses or anything. It is simply by being in contact with the surrounding air that these engines transfer their heat away onto it and cool themselves.
You can easily recognize air cooled engines by the increased number of fins on their cylinder heads.
And that's really all there is to air cooling and this makes air cooled engines dead simple and pretty which also makes them lightweight and very easy to maintain and makes their production very cost effective. But there is a price to be paid for this simplicity. The first is uneven cooling. If we imagine an air cooled engine in the stream of air we can see that the front part of the engine exposed to the air does indeed get cooled, but the back part of the engine obviously isn't in the air stream which means that it won't be cooled as well.
Air cooled engines rely on running richer than liquid cooled engines to ensure that they don't overheat even when outside temperatures are high and the vehicle is stationary. But running richer than required not only reduces power potential but it can also dramatically increase hydrocarbon emissions.
Now the line between oil cooled and air cooled engines can be blurry. The first reason is that all oil cooled engines are also air cooled and you will find that oil cooled engines feature the same cooling fins on their heads and cylinders as can be found on air cooled engines. The other issue is that many air cooled engines such as the Volkswagen and Porsche air cooled flat fours and flat sixes feature an oil cooler so some people actually refer to them as oil cooled rather than air cooled.
But a clear distinction can be made and an engine can be qualified as oil cooled not simply by the presence of an oil cooler but by the fact that a part of the oil is circulated through dedicated channels with the clear purpose of cooling the engine rather than lubricating it. A telltale sign of an oil cooled engine will be increased oil capacity. One of the most widely known representatives of oil cooled engines are engines made by Suzuki featuring their SACS or Suzuki Advanced cooling system. The system was used extensively on GSXR model bikes from 1985 through 1992 and was also featured on the Bandit, GSF as well as DR650 bikes.
So the oil cooling system has the advantage of being able to circulate the entire circumference of the combustion chamber which means that it takes heat away right from the source and allows even cooling of all parts of the engine. The drawback is the increased complexity due to the presence of the radiator and additional oil channels and hoses as well as the increased servicing cost due to the increased oil capacity.
But there's another drawback to oil cooling, and it's the heat capacity of oil which is inferior to the heat capacity of water. Engine oil typically has a heat capacity of around 2 kilo joules per kelvin. This means that it can absorb 2 kilo joules of energy in the form of heat before it's temperature increases by 1 kelvin. Water is far superior in this regard and it has a heat capacity of 4.18 kilo joules per kelvin. This means that water is capable of absorbing twice the heat of oil before it's temperature increases. A mixture of water and antifreeze or coolant flows through dedicated coolant channels throughout the engine block and cylinder head and absorbs heat away from the engine. To ensure proper circulation water cooling also requires a water pump. The pump is usually driven by the engine via a belt although the water pump can also be electronic in more recent vehicles which reduces the parasitic load on the engine. Coolant is passed through a radiator which dissipates the heat absorbed from the engine into the surrounding air. Another key component of the system is the thermostat, it prevents the coolant from circulating through the radiator until the engine reaches operating temperature.
A special thank you to my patrons:
Daniel
Daniel Morgan
Pepe
Brian Alvarez
Jack H
Dave Westwood
Joe C
Zwoa Meda Beda
Toma Marini
00:00 Intro
01:11 Air cooling
07:31 Oil cooling
10:58 Water cooling
#d4a #aircooled #cooling