I am thinking of getting a new ATV and looking at a 400 AC..it is air cooled. Is water cooling better and why ...thanks

 

There is no definate best although overall I'd say that water cooled is better. The bigger a quad is, the more likely you'll find that it's water cooled. A lot depends on the conditions in which you ride and how fast you go.

No doubt that water cooling is better if you are running at slower speeds or are doing slow speed working with the quad. As you would expect, air cooling needs air flow over the engine to work. Low speeds or lots of mud on the engine cooling fins will make it run hotter. Water cooled quads are not without their problems - radiators are usually placed in areas where they are llikely to get clogged with mud.

Some air cooled quads are assisted by a cooling fan, some by an oil cooler and some with both. I went on one ride on a dry, dusty day on trails that had several mud crossings. We had a P650 and Rincon (water cooled), an Eiger (air cooled with fan and oil cooler) and two Ozarks (air cooled only). Both the P650 and the Rincon constantly overheated as the dust mixed with the mud and clogged their radiators. Had the trail been a little wetter or been totally dry there would have been no problems, but as it was the two water cooled bikes had to limp home - even after several attempts at cleaning out the radiator fins.

Jaybee

 

In addition to Jaybee's posting (which I agree with) I would like to add or expand on a few points.

First - a lot depends on how you ride. When I started I rode 2000+ miles and never once plugged up the radiator. Then I started riding with some real mud bogging guys and I've been steamed up several times. So if your not going bumper deep into the snot or towing another quad 20 miles out of woods - getting plugged up and over heating is not all that common. Can be - but doesn't have to be. Some of us have rigged the on-board pressure washer for just such occasions. (12v RV water pump and a couple of canteens..)

This is a old post on I had on the subject of engine cooling - maybe this information you already know..

Engine cooling is required because of the heat created during the combustion process. The more power the more heat - the more heat the more difficult it becomes to get rid of that heat. As compression ratios are raised and the engines are run at higher rpm's, at some point you just can't make the cooling fins any larger or fit any more fins on the engine and you cant get 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.

Many believe that the seizing of the piston to the cylinder wall is caused by rapid expansion of the piston but more often it is usually the failure of the oil to keep the piston and rings from becoming welded to the cylinder. As the lubricant 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.

Most air cooled engines have a considerable cooling safety factor built in. They are designed with allowances for long up-hill runs, hot days and even provide 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 products do is take away any over-heat safety margin. Exhaust modifications are in this arena.

Regulated engine temperature adds considerably to the longevity of a engine. Cold engines are not being lubricated as well as they should and engines running hot are pushing clearnce tolerances and lubrication to their limits. Fluctuating temperatures expand and retract engine components and increase wear.

Early in the design stage the engine designer decides how much power he wants from a given displacement size. 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 choice to squeeze more horsepower out of the engine. Recall the earlier "at some point they just can't put enough cooling fins on the engine"? Now its time to go another way to move the heat away from the cylinder and regulate the engine operating temperature... water.

Water is a whole lot better at conducting 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 returned to the engine to pick up some more heat. 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.

As ATV's designs become more sophisticated with body panels that protect the rider from hot engine parts but also restrict air flow to the engine - and riders demand more horsepower from increasing engine displacements you see why the trend to more water cooled engines.

The oil-cooled systems are a great alternative to air-cooled and a improvement over the weight and overhead of a water jacketed engine but they do not provide the same regulated temperature as water-cooled engines do.

Depending on how and where you ride you may want to choose between oil and water cooled for maximum power and engine life.