October 9, 2020

Remember that bike you had as a kid? It allowed you to fly around the neighborhood with your buddies. It might have had 10 different speeds to choose from, maybe six, maybe even none at all.

Now think of that 21-speed beauty currently hanging in your garage. Your legs might not be as spry, but the wheels do a lot of the work. You can shift to allow as much give as you need to make it up – or down – hills with relative ease and either cruise or pedal hard on the straightaways.

A viscous fan clutch can cool a truck, tractor, construction machine, power generator or mine hauler’s engine with a similar amount of flexibility.

Viscous drives control how fast an engine fan spins with remarkable accuracy. Oil is released from a reservoir into grooves that allow for increased or decreased friction depending how much cooling is needed. This target temperature is determined by the vehicle’s ECU, which is tied to a controller that opens and closes a valve that releases the viscous fluid. The fluid is then pumped out of the working area and into reservoir.

Viscous fan drives have been a staple in European on- and off-highway applications for the better part of a decade. Most off-highway equipment in the United States deploys them, as well. And long-haul trucks are starting to convert to this new technology in waves.

Here are five reasons why:

1. Viscous fan drives deliver only the amount of cooling needed – nothing more, nothing less.

Fully-variable clutches are the most technologically advanced, efficient option available when it comes to engine cooling systems. Legacy technology is either «on,» or «off» or at the most features two speeds. While this is useful in some applications, viscous drives offer a greater degree of precision.

That has a bevy of benefits.

2. When an engine can devote less energy to cooling and more to turning wheels, that means fuel savings.

When Georgia trucking fleet owner Mike Frost retrofitted his fleet of vehicles with a fully-variable RCV250 drive from Horton, he saw fuel economy improvements of more than 1/10 of a gallon.

That’s because his vehicle’s engines are receiving optimized cooling at every moment the truck is on. When the engine’s hot and needs to be cooled, the RCV250 turns faster until optimal temperature is reached. Once that happens, the fan slows way down, consuming less fuel.

This advantage isn’t just limited to long-haul trucks. Farmers, construction workers and miners all use diesel fuel to get their job done. If their equipment has a viscous fan clutch, they’re able to get more out of their engine before needing to refuel.

3. The lower a fan drive runs, the less noise it creates.

That means a more comfortable experience for an operator. But it also means complying with noise regulations that continue to tighten as the world’s population becomes more urban.

The EU’s Outdoor Noise Directive imposes strict limits on allowable volumes emanating from outdoor machinery. Engine fans are one of the largest sources of noise on a vehicle, so increasing noise emissions rules are a large driver for adoption of viscous cooling technology in Europe.

It’s coming in the U.S., too, as the Occupational Safety and Health Administration and Environmental Protect Agency explore ways to limit noise.

4. Viscous fan drives are just plain better for the environment.

Every time an internal combustion engine runs, particulate matter is created as a biproduct of the engine cycle. But proper cooling can limit it and thus significantly decrease carbon emissions.

With varying emissions regulations around the world, there’s a lot for a design engineer to keep track of. But any engine manufacturer can rest assured they’re both being a good steward of natural resources and achieving government compliance when they specify a viscous fan drive.

5. Fully-variable clutches handle swings in temperature better.

In some of the world’s roughest working environments, including mines, spikes and extreme dips in temperature can have a negative impact on engine components. But by holding oil in the reservoir when the engine isn’t running, viscous drives can help vehicles start up faster in cold weather. And by responding directly to the engine’s cooling needs, variable-speed clutches can help it perform better when the sun is beating down.

Of course, viscous clutches aren’t the only option available. Some long-haul applications see their drive disengaged up to 90 percent of the time, so they still benefit from an on-off drive.

On-offs are also simple to replace, although viscous drives have a long shelf life too, with many coming maintenance-free.