A GROWING number of ATV manufacturers now fit liquid-cooled engines instead of air cooling in their larger machines.
The sales brochures provide little guidance about the benefits of each system, so which is preferable?
As average engine size has increased, cooling capacity has been boosted to cope with the extra heat generated. Air cooling remains adequate for small and medium-sized machines, but liquid cooling and fan-assisted oil coolers are used on larger machines.
Kawasaki started fitting liquid-cooled engines in its KLF 400 model in the early 1990s. Jack Ford, ATV marketing manager with Kawasaki says the liquid cooling is beneficial as the larger machines are expected to work for long periods under heavy load conditions.
Kawasakis latest ATV, the KVF400 was introduced at the end of 1998 and this features a similar liquid-cooled power unit, but a smaller model recently launched in the US has conventional air cooling.
"Although liquid cooling is the way forward on larger ATVs, there is no need for this on smaller machines which generally carry out lighter tasks and generate less heat," says Mr Ford.
Polaris has fitted liquid cooled engines in its larger machines for several years, and the recently introduced Polaris 455cc diesel also has this cooling system. The British built Diablo 611cc diesel powered ATV has a two-cylinder liquid-cooled engine, and the manufacturer claims that a big benefit of this is quieter operation than air cooling.
On Suzukis recently introduced range of ATVs, the largest 493cc model features a liquid cooled engine, whilst the mid-sized 280cc version has air and oil cooling. A smaller 246cc model has basic air cooling.
Yamaha and market leader Honda remain loyal to air cooling, although their larger machines do have engine cooling fans and external oil cooler radiators. Oil from the engine is circulated through a small external radiator, a thermostatically controlled cooling fan ensuring an adequate flow of air through the oil cooler even in heavy work when low travelling speeds produce little natural air movement.
Mike Bush, divisional manager for Yamaha UK Power Products, says there is no particular demand for liquid cooling in the UK, and believes it increases maintenance requirements.
He says that as a considerable amount of ATV work is carried out in the winter, damage to the system by freezing could be a problem if the cooling system is not correctly maintained. Also, a radiator can be damaged, or blocked with debris or mud, but he does concede that air-cooling fins can also become blocked.
Yamaha manufactures the most powerful machine available in the UK, the 595cc Grizzly, and Mr Bush insists the air and oil cooling systems fitted have proved more than adequate for this powerful machine.
Mark Jeram farms near Great Dunmow, Essex, and over the last 12 years has owned three large air-cooled machines. His first, a 350cc Honda was replaced by a 400cc model and he now runs Hondas largest machine to date, the TRX 450 Foreman.
Mr Jerams land is mostly heavy clay and very susceptible to rutting and compaction. "I see the extra weight of a liquid cooled ATV as being a disadvantage," he says. "Liquid cooling would not attract me, as I have never had any of my air-cooled machines overheat. I like the simplicity of the air and oil cooling system, and any extra complication would concern me."
Nick Bird farms 283ha (700 acres) of arable land near Hadleigh, Suffolk, and runs a liquid-cooled 499cc Polaris and an air-cooled Honda TRX350.
His Polaris is two years old, and when the machine was purchased new, Mr Bird had no preference for air or liquid cooling. He says the liquid-cooled Polaris engine seems quieter than the air-cooled unit, and he has found little extra maintenance necessary with the liquid-cooling, apart from checking the coolant level occasionally.
Both ATVs are used for general farm work and because Mr Bird has had no problems with either system, the choice of cooling system will not be a big factor when choosing an ATV in the future.
Another farmer with experience of both cooling types is Andrew Baker, who has a 500-sow outdoor pig unit near Ipswich. These are housed over 26ha (65 acres) and the land is light and can be very dusty in the summer.
He has run a liquid-cooled Kawasaki KLF 400 alongside an air-cooled Honda TRX 400. "The dust and winter mud has proved no problem for either machine and I have not experienced much extra maintenance requirement with the liquid cooling. Kawasaki fits an insect and debris mesh in front of the radiator and we have had to bang it out occasionally, but we have had no problems."
Mr Baker has no preference for air or liquid cooling if he was selecting a new ATV, but he finds the liquid-cooled Kawasaki gives off less heat from around the engine, making it more comfortable in the summer but less attractive in the winter.
Few claims are made in manufacturers sales literature for the use of either type of cooling system and the design, particularly of larger ATVs has come so far now that whichever is fitted, it should be adequate for the particular machine.
Benefits of liquid cooling may include quieter running, and maintaining a more consistent engine temperature, but the units usually require more maintenance and are more complex.
Air-cooled units tend to be lighter, simpler to work on and more than adequate for coping with heavy farm work. Users experience suggests the choice of cooling system need not be a big consideration when choosing an ATV, and there are more important factors which should be considered first. *