How to get the most out of your fan clutch

Common fan clutch

A lot of the talk surrounding multi-speed engine cooling fans is around all the fuel and performance benefits. It is true, but not universally. Luckily, knowing if a single-speed or 2-speed fan is right for you is pretty straight forward. Below we’ll look into the benefits, and the drawbacks, of both systems. We’ll also look at what to do if you realize you don’t have the application on your trucks and you don’t want to bust the bank replacing your entire fleets fan clutches.

Engine fan basics

The fan will only turn on in one of three situations. For the air conditioning system (which has nothing to do with this article, but should be kept in mind when a complaint of ‘fan always on’ is made). When the engine has gotten to a temperature where any further and unnecessary wear or damage could occur. And lastly, when the driver sees that the engine is at a good temperature, but is about to take on a heavy load (such as a fully loaded trailer and a steep, slow hill).

Most of the time, the fan and the fan clutch that came with the truck, or, whichever fan the dealer recommends for the unit’s engine and application, is hardly worth any study or consideration. That being said, if you make the wrong decision, it can cost you a lot of money in fuel, maintenance, and breakdowns. The deciding factor to whether you would need a single-speed or dual-speed fan clutch is whether or not the unit will be consistently hitting relatively high speeds.

Single-speed vs dual speed clutch

A number that floats around when we talk about engine fan air flow or the ‘wind’ it creates, is 35 miles per hour. Or just over 55 kilometers per hour. Many will also claim that so long as the vehicle is running under 35 mph/55 kph, then the fan automatically turns on. It may be that in some situations this is acceptable, or even good, but it’s rarely the case.

If a fan were to always turn on when the vehicle is traveling ‘under speed’ it would cause weight to the drive train, therefore using more fuel. Also, it would take more fuel to get the engine to operating temperature. This is important for not only proper fuel economy but to get all those HP’s out of the engine and move those heavy loads. Cold engines typically mean lower horsepower.

That being said, there are some applications where higher speeds are known to be a small percentage of a given unit’s work day. Common examples are off-road units, dump trucks, excavators, etc. The most recognized example is the refuse (garbage, recycling, organic waste) truck. For trucks like these, getting to and from the job may represent as little as 5-10% of the work day. So for these trucks, having the fan on a low speed at all times is not such a big issue. It may be difficult to warm up the engine on a cold day, but rarely will the low speed of a fan prevent the operating temperatures altogether. So basically there is very little downside for these applications. The upside is that since the vehicle is getting little to no natural air flow when working, the low speed of a dual speed fan will be a moderating force for an engine that is probably constantly accelerating and braking. There will always be a minimum of air flow with the dual speed, preventing the full fan from turning on.

There is another reason why the dual speed is so beneficial. When a fan clutch engages, it is relatively hard on the clutch. Sure the clutch is made to be slammed on but that doesn’t change the fact that the less often a fan needs to engage, the longer it will last. Having the low, constant speed reduces the number of engagements. How a low speed works causes pretty much no wear at all. The low speed works by a magnet, or series of magnets inside the clutch housing. This means there is physical contact for the fan to engage. This also means that with a dual speed fan, you cannot turn it off completely. That is where the fuel expense comes in.

Correcting for the wrong application

2-speed clutch parts

If you decide or are worried that you may be using a fan clutch that is less than ideal for your work environment, it doesn’t have to cost you a thousand dollars per truck with parts and labor to replace the units. There are ways of modifying each for relatively low cost, and possibly no cost of parts.

If you have a single-speed fan clutch and feel the need for a dual, this is by far the more expensive problem. But maybe not as bad as one would expect. All the major fan clutch manufacturers sell popular model magnet kits for installation on your pre-existing clutch assemblies. This means a small cost of parts, and an installation very similar, but much easier than rebuilding a fan clutch. And retrofit kits always come with easy to follow instructions. Follow the instructions properly, and there will be no problems.

If you have a dual speed clutch and have come to realize that not only are you spending more in fuel, but your engines may be having a difficult time reaching operating temperature, then the solution is much easier. What can be done, and I can say it is very simple from experience, is remove the fan clutch, and remove the magnets. Often you don’t even need to take apart the fan clutch. A word of warning, however, the magnets are pretty strong and can pinch a mechanic. Also, I’ve seen it happen that a magnet somehow stuck to the back of a fan assembly, causing the fan clutch, and the belt splines to be out of alignment, causing damage. So be careful that the magnets you remove are accounted for, not to have them stick to your engine after the job.

Conclusion

That is about all the practical information there is to know about fan clutches. The actions mentioned above really should be done by an experienced mechanic since doing the job wrong could cause an injury or damage, but it doesn’t need to be a huge concern for your truck or your fleet.

Drive safe,

Kevin Gauthier