Air cooled V.S. Fluid cooled engines.?

Question

I was wondering what the differnece between Fluid cooled and air cooled engines are. ( Pros/Cons for both) Ive heard that fluid cooled shorten the life of the bike. Its just another thing to break ect. I was also woundering if air cooled systems get the job done. Do those bikes have any problems on hot days. Thanks

Answer 1

Let's keep this simple...we need to cool engines because they create heat during the combustion process. The more heat generated, the more difficult it becomes to get rid of that heat. As you raise compression ratios and run the engine at higher rpm's, at some point with an air-cooled engine, you just can't make the cooling fins any larger, can't fit any more on, and you can't blow enough air over those fins to get rid of the heat faster than it is being produced. This is when the dreaded "piston seizure" usually takes place.

While most people believe that the welding of the piston to the cylinder wall was caused by excessive expansion of the piston (this too can happen), but it is usually the failure of the lubricant to keep the piston and rings separated from the cylinder. As the oil gets hotter it gets thinner, at some elevated temperature it stops being a lubricant...the lubricating film breaks down and the destructive metal to metal contact begins.

Almost all air cooled engines have a considerable cooling safety factor built in. The designer of an air cooled engine makes allowances for long up-hill runs, hot days and even provides for some out-of-tune conditions. There is no reason to be wary of air cooled engines...unless you start doing things to your engine that start cutting into this safety margin.

The makers of bolt-on performance equipment rely on this safety factor. Because, when their products squeeze more horsepower from your engine, they also generate a lot more heat. What some of these go-fast products do is take away any over-heat safety margin.

If we fully understand what we might be getting into, OK... but the swami has never seen an advertisement for horsepower increasing products with the notification: "this equipment will probably shorten the life of your engine and also might lead to catastrophic failure, and by the way, good luck with your engine warranty"

So when you see an air-cooled scooter engine putting out surprising horsepower, you are looking at an engine living a risky life in the fast lane. The swami can report from experience that the romance of souped up engines fades in direct proportion to the distance you are from civilization when the seizure occurs. But the swami digresses...what about the water?

At the very early stages of engine design, the engineer decides how much power he wants from a given displacement. He can play it safe, keep the compression ratio, (and a lot of other parameters) conservative, generate less heat and comfortably cool with air...or...make the decision to squeeze some more horsepower out of the engine. At some point they just can't put enough cooling fins on the engine and it's time to go to another way to move the heat away from the cylinder ... water.

Water is a whole lot better at conducting heat than air. Have you ever seen a blacksmith drop a red-hot bar into a tub of water to cool it off quickly? Did you ever see him wave it around in the air to cool it off quickly? NO! The water does a much better job of conducting the heat.

DON'T TRY THIS AT HOME! JUST IMAGINE THIS AS THE SWAMI EXPLAINS IT. A pizza maker will put his entire arm into a pizza oven with air inside that is around 450 degrees F. He does not get burned immediately because the air is such a poor conductor of heat, it would take time to begin to cook his arm. Now, what would happen if he put his arm into water that is boiling (which is only 212 degrees F.) The results would be immediate and terrible. Yes, water is a better conductor of heat than air.

So, the engine designer loses the fins and puts a watertight jacket around the head and cylinder to contain the water that will carry away the heat. The water is circulated through tubes in a loop from the cylinder to a radiator, where the water is cooled by... AIR!, then the cooled water is returned to the engine to pick up some more heat.

After all this, the engine is still cooled by AIR? What's going on here? The water is the vehicle for carrying the heat from a place where the engine designer can't put enough cooling fins, to a place where he can put enough cooling fins. Looking closely at a radiator you will see many small tubes and thin fins. This gives a very large surface area exposed to the air, where the heat is carried away.

As scooter designs become more sophisticated with tightly fitting body panels that restrict air flow to the engine and as riders demand more horsepower without increasing engine displacement (in some parts of the world you pay taxes base on displacement) you will begin to see more water cooled engines.

So, if you have a water cooled engine, there's some more weight, and a few more components to check and care for. And, most importantly, keep that radiator free of bugs and debris because, after all, it's still an air cooled engine.

Answer 2

Air Cooled Engines

Answer 3

I wouldnt say that liquid cooling shortens the life of an engine. If anything, it increases it. Yes, liquid cooling adds complexity to an engine but generally lets and engine run at a higher level of output for a longer time more safely then air cooled ones do. But there are more things to go wrong, like hoses busting and water pumps failing, etc.

That being said, there is nothing wrong with air cooled engines. When a manufacturer makes a bike they decide what type of engine to use depending on what the intended use of the bike will probably be.

Look at Harley Davidsons. Almost every Harley ever made has an air cooled engine. But they are not high performace engines so what they are designed to do (cruise around all day at low RPM) they do very well.

I own a Suzuki Bandit 600 and it has an aircooled engine. I ride it all the time in Texas summers (very hot) and it performs just fine.

Most modern sport bike engines are liquid cooled so that they can perform at a high horsepower output for a very long time without any serious engine problems. You will also find liquid cooling on most modern bikes, regardless of type. Cruisers, tourers, dirtbikes, sport....it usually just helps performance and engine life.

But air cooled engines work just fine to. Dont be afraid to buy an air cooled machine. They work fine. A lot of people believe they give a maching more character, or more of an old world feel. Like from a time when all bikes were air cooled.

Hope this helps. Ride safe and have fun.

Answer 4

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RE:
Air cooled V.S. Fluid cooled engines.?
I was wondering what the differnece between Fluid cooled and air cooled engines are. ( Pros/Cons for both) Ive heard that fluid cooled shorten the life of the bike. Its just another thing to break ect. I was also woundering if air cooled systems get the job done. Do those bikes have any problems on...

Answer 5

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a radiator is a fairly easy part to assess the condition. starting with a visual the radiator should have no sins of leaks at the tubes. nextly look into the tank and see that the tube openings are clear and not coated with a crusty almost barnicle looking substance this would be a sign the time has come for a new one. nextly the touch test. I suspect you have a cross flow radiator meaning the tanks are on the ends rather than top and bottom. while the engine is running a notable temperature change should occur from the right side to the left as it be cooling the water as it passes thru the core. flushing the cooling system is good but too much can be bad. in an older engine pockets of rust build up in the walls of the heads, intake and block. if chunks get free they can block smaller passages causing flow problems in the engine. also freeze plugs are often rusting from the inside out and one chunk free could spell freeze plug job and those buggers like to go out when you least expect it.

Answer 6

Good question ff. A lot can be said. For my 2 cents worth; Liquid cooled engines are quieter by design, having jackets
around the cylinder that contain the fluid. There aren't any inherent problems. As little as or less than a car may have.
Air cooled engines have been around forever, dissipating heat through the mass of fins and air flow on the cylinders. If
the bike is used for its intended purposes, it works fine. Harley-Davidson tested models in a "heat shed" in the desert. It was a walled area to block any wind with no roof to block the sun. Bikes were left to run for various intervals (hours) on end and showed no heat related problems.

Answer 7

Liquid cooled engines operate at a more constant temperature, so they live longer and are more reliable.
Air cooled depend on moving air so if you are in heavy traffic they can get mighty hot.

Answer 8

Everyone has made very valid points. In addition to the points already made, on motorcycles one of the major reasons most large street bikes are watercooled is for emmission control. Watercooling maintains a more constant temperature which maintains a more even emmission output. The greater the temperature fluctuation, the greater the emmission output varies and control is like trying to hit a moving target.

Answer 9

why buy old technology?
Get a newer technology bike, liquid cooled, shaft drive, overhead cams, and multi valves per cylinder and fuel injection.
Air cooled engines are for lawnmovers.

Answer 10

air cooled may blow up in traffic, liquid cooled is gay.