Cool Runnings? How to avoid overheating – Part 1: The Bike

Cool Runnings? How to avoid overheating – Part 1: The Bike

Riding a motorcycle can be hard work. Whether you are muscling your adventure bike through a Moroccan desert or slogging your trail bike through axle deep mud in a forest in the middle of nowhere, it’s common for both you and the machine to get a tad hot under the collar.


And it’s not as if overheating can only occur when the weather is hot. It might be below zero according to the Met Office, but if you are fighting a bike weighed down with pounds of mud up a gripless bog, that motor is going to boil up as if you were in the Sahara.


So with that in mind, we thought we’d run through a few ways to keep the two of you cool through the rigours of your riding. We’ve split it into two sections, one for each to keep it fair. You won’t necessarily want to do everything in both lists, but each step will have a significant difference to the health and performance of both you and the bike.

We’ve illustrated products that we have used or have experience of, but clearly there are other options on the market so do the research as to what will be appropriate for your bike.


For the first instalment, we’ll look at the changes you can make to your motorcycle.


So just to cover ourselves here, a word of caution. Not all these suggestions will be appropriate for every bike. If your bike is shiny and new, making even small changes to the cooling system may affect your warranty, so be careful as to how much you do if that’s a concern. We would also remind you to check your owner’s manual before making any changes. Clear? Good.

The System


OK so the principle of water-cooling on bikes it that your cylinders have a water jacket around them containing usually a mixture of water and anti-freeze. The liquid is pumped round the cylinder, or cylinders, where it gathers their heat and once up to temperature, the thermostat valve directs the fluid to the top of the radiator. Travelling through the tubes within the radiator cools the fluid thanks to the flow of cool air than should be travelling through them as you move. Once through, the fluid travels back to the pump before returning to the same journey, endlessly circulating to keep the motor on song. If the system gets too hot, fluid will be expelled through the radiator cap into either an expansion tank or the ground.


So you can see that within this system there are a number of different components that can affect the cooling. We have the fluid, the radiators, the cap, the hoses, the pump and lastly, although it’s not a component, we have the air flow though the radiators. Improving or changing any of these elements will improve or change the cooling of your bike – simple.

Capping the pressure

The radiator cap is the bit that holds the fluid in after filling up, but also allows the fluid out in the case of overheating, or ‘boiling up’. The temperature at which it does this varies according to the pressure rating of the cap which is usually stamped onto the cap itself, usually in bar. Once you cooling system warms up it becomes pressurised as this allows the motor to run higher temperatures than the fluid would otherwise withstand without boiling.


Now because the hotter the fluid gets without boiling over, the better it can cool as it flows through the radiators, then uprating the cap to a higher pressure rating can allow that change. A standard cap is usually around 1.1 bar, where 1 bar is normal atmospheric pressure, so you can see the pressure within the system is slightly higher. Uprating the cap to something like a 1.3 or even 1.6 will allow the system to run higher pressures, hence higher temperatures which will in turn cool better as the fluid pumps through the radiators.


Again a word of caution here – because uprating the cap will increase the pressure, your hoses need to be up to the job otherwise you’ll get leaks, which ain’t good. If you are going down this route, you may need to uprate your hoses, but at the least, start with a small change to a slightly higher pressure, rather than going straight to the 1.6 bar cap. That said, as can be seen in the photo above, we run a 1.8 cap on our 2013 KTM EXC250 with no issues. We use waterless coolant at present, but when the bike was purchased from the initial owner, it ran this cap with stock coolant mixture.

As with anything involving your cooling system, be careful, as hot fluid is involved here! Never open a cap when the engine is hot, and unless the engine is stone cold, cover the cap with a large rag in case residual pressure blows out any hot coolant.

Happy Hoses

When your bike left the factory, the manufacturers fitted it with bog standard rubber hoses. Now there’s nothing wrong with these and they will do the job intended, but if you are looking to uprate your system, then you are likely to need to uprate your hoses.

The most common upgrade is to a custom set of silicone hoses. These will ideally be bike specific, so that all the curves and bends are in the right places and if you bough a good set, all the messy connectors and cheap as chips hose clips are replaced by preformed joined hoses and stainless clips.


With a much smoother internal surface, better hose junctions and often a slightly wider internal diameter, silicone hoses will help the coolant to pass through the system far more efficiently. As an upgrade for a dirt bike that costs around £60 it’s almost a no-brainer. For an adventure bike, it might need a bit more investigation due to the complexity of the motor and the accessibility of the various components, so do your research.

As an additional step, many silicone hose kits actually cut out the standard thermostat from the system that you bike will most likely have come with. This makes sense as the additional plumbing only serves to complicate the system and restrict flow. In cold countries you may not want to do this as you don’t want the fluid to start going through the radiators until the motor is up to temperature. For more temperate climates, ditching the ‘stat will make little difference apart from the bike taking slightly longer to warm up as the coolant will be circulating from the moment you start the motor.


As a side issue, though clearly very important to the peacocks within the paddock, silicone hoses come in all kinds of pretty shades from colour matches to your bike to patriotic versions and if you’re a badass mother – urban camo effect.

Pay you money take your choice, as long as it’s not pink ….

Water or Wetter?

Water-cooling of combustion engines has been about almost since the invention of cars back in the latter parts of the nineteenth century. Even then, engineers knew that if motors could run hotter they could run higher tolerances, but that in turn would necessitate a way of dissipating the heat.


But despite this it took right up until the Second World War to bring any change to water being the coolant of choice. Anti freeze had been used in colder conditions, but this tended to be only in the winter months.

But as is common, war brought on technical advancements and the development of high-performance aircraft engines bought on the development of coolants with higher boing points, commonly ethylene glycol or a mix of this and water. The fact that the same glycols could be developed for their anti-freezing properties and corrosion inhibiting properties was another major factor that lead to motor manufacturers transferring the technology to their cars.

So fast forward to today and although bikes took absolutely ages to become water-cooled, virtually everything we ride today has the same technology as motors just after the war – namely a radiator based cooling system running a glycol-water coolant.


But is water the best still? Well companies like Evans don’t believe so and their waterless coolant system is just that – there is no water whatsoever involved, and their fluid is added neat to your cooling system. Evans claim significant improvements to the cooling efficiency over the usual water and glycol, and without any water around the metals in your engine, internal corrosion is also significantly reduced.

To use the Evans product, you system needs to be fully drained and then a prep fluid is added to purge all water from every nook and cranny. Once this is fully drained, the waterless coolant is added to the required amount, you click on the cap and you are good to go. Our KTM EXC250 runs this and never, ever overheats.

Of course for a bit of balance here, if a bike with Evans Coolant in it overhears, then it’s not ideal to top it up with water out on the trail, and you are unlikely to be carrying a spare bottle of Evans Coolant with you …

Pump it, pump it

So now we’ve looked at three elements within the cooling system. The new cap allows higher pressures, the hoses flow the fluid more efficiently and now the fluid is all twenty first century tech rather than pre-war thinking. What’s next?

Well maybe you might want to look at the stock water pump. Again like the hoses, it will do the job, but if we are looking to upgrade things, then maybe getting the fluid round the system faster might be a good idea? Luckily there are options on the market, but they tend to be more focussed to the dirt bike end of the market, so finding an equivalent for a KTM 1290 may be more difficult.

If you’ve never heard of Eyvind Boyesen then you need to brush up on your dirt bike history. Back in 1972, Boyesen developed the first dual-stage reed valves that would revolutionise racing and later become standard equipment on just about every two stroke in the world. The man himself died in 2010, but his legacy continues through his company Boyesen Engineering that makes all manner of utterly gorgeous and thoroughly wonderful performance upgrade parts for everything from snowmobiles to outboard motors, quads to dirt bikes.


But the part we are interested here is the Boyesen Supercooler. It’s a straight swap for the stock pump impeller and water pump casing on your bike. The Supercooler is almost universal across most US motocross teams and many in MXGP, and serves to dramatically improved the flow of coolant through the system across the entire rev range, bringing significant improvements to the cooling efficiency of the system. Enough said.



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Fan Frenzy

For the next part of jigsaw, we need to look at airflow. For road bikes, getting sufficient airflow through the radiators is usually not a problem. Travelling at anything over ten miles an hour will move enough air through the radiators to keep things on an even keel, so once you are up to motorway speeds and the motor is working harder, the increased air flow matches the increased load and resultant temperatures.

It’s only when those same riders have to pootle through traffic when things get more tricky, and so the manufacturers include thermostatically controlled fans that click in when the temperature rise, forcing cool air through the radiator.


Yet although this simple technology has reached some dirt bikes, it’s by no means universal which is odd considering these bikes are commonly plugging through deep mud at slow speeds when little or no airflow is going through the radiators.

But help is at hand in the form of aftermarket fan kits, and it’s a simple upgrade that everyone from a child upwards could fit. Looking at the stock KTM version, all the components are there including a temperature gauge so you can see exactly how hot the system is running. The kits usually come with a thermostatically controlled switch, but it’s not too complicate to supplement this with a manual over-ride if you want to stop things getting hot in the first place. At around the £100 mark it’s another no-brainer for the serious off-roader. It’s a shame that the other manufacturers are not quite so good at supplying ready to go kits!


Expansion plans

For most dirt bikes when the coolant gets too hot and boils over, it ends up going out the expansion tube and onto the ground. For odd occasions, this isn’t too much of an issue, but if it occurs regularly during a ride, pretty soon you will be running with less coolant than the system needs. It’s a vicious circle that leads to more overheating.

But this doesn’t happen with road bikes and certain enduro machines as they have an expansion tank to catch the fluid. Once the temperature reduces the fluid is drawn back into the system, thus maintaining the correct levels.

But help is at hand in the form of retro-fit expansion tanks like the one shown above from British firm GMX. It’s an easy to fit option that will catch a significant amount of fluid and stop it leaving the system, and having used one if these on a fair few enduro bikes, we can vouch for their effectiveness.

Oh and as a spin-off benefit, they look super-trick factory racer cool – what’s not to like there?

Oversize me!

The final option we’re looking at to keep your bike running as cool as possible is to actually change the radiators. This isn’t a cheap option, but fitting larger radiators than stock is a surefire to get more fluid running round the engine and if that fluid is running through through a larger surface area, then the cooling will be greater.

OS Radiators are not usually massively longer than stock, but clearly are bigger so need to be bike specific to pick up on the right mounting points and avoid other components at the front of the bike. They will have far better flow-through thanks to the core which can be up to 10mm deeper than stock. Manufactures like GMX reckon on around a 20% reduction in running temperature which is massive and goes to justify the relatively high initial cost.

While the market for these parts is mostly for off-road machines and motocross bikes, specialist radiator firms like GMX make these components each and every day. That means that even if you can’t see a listing for an Africa Twin, contact them and they will be able to discuss custom made options.

OK so that’s all for the moment. As we said, every one of these will make a difference, but you don’t need to go for everything in one hit. Small steps will allow you to assess the improvement you are getting with each upgrade.

In the next blog we’ll look at the best ways of keeping you cool – and we are not talking a pair of mirrored Aviators and a leather jacket …

Lets us know how you get on with our suggested upgrades, and if you have any other suggestions, share them with the class!


8 comments on “Cool Runnings? How to avoid overheating – Part 1: The Bike

  1. Ading moore fuel is probley the single most effective solution to running hot slightly rich has numeriouse benifits in hot climate longtivity and cool running enough said

    1. Thanks for the input Ian – more fuel is a solution but it’s an expensive one and in remote areas will mean you may end up miles from anywhere without fuel. Uprating th cooling system is a far better way of improving the cooling!


      1. Very good stuff. I live in Costa Rica. I just bought a 990 Adventure to satisfy my middle age renegade tendencies. However, the monster, although super sexy and lightning fast for this country, is too hot to ride. And San Jose, about 3,000 feet, is not even hot. On a 85 degree day, I reach “last bar” in about 4 clicks. And there’s always traffic ! Something is wrong. I need to cool it down. Here’s what I’m thinking:

        -change out the stock mufflers for “Arrow” mufflers My Australian mechanic at AG Motors (who seems to be just great) tells me that the catalytic converters are the big culprit here. Will this help ?

        -silicone hoses
        -new water pump with better quality impeller
        -larger radiator ?

        I love the bike. My last bike, a KLR 650 was also great. However, this klr is a bit taller (which I like), faster, and a true Rockstar! I really want to make this a “weekend rider” and keep it for the long haul. The bike is great, except for the heat!

        Any suggestions ? Rick in Costa Rica

        1. Hi Rick

          The big twins generate a lot of heat, particularly on that back cylinder. Certainly the cat will generate a lot of the problem, but there are clear environmental implications of removing this part – your decision! The hoses, radiator upgrade and pump will help a lot, as will going to a waterless coolant. If you fit a direct fan switch then you can get it running as soon as possible, rather than waiting for the thermostat. You can use reflective foil on certain parts to deflect the heat away, and you could look at an uprated oil cooler too. Failing that – trade it for an EXC500 and you’ll love it ….


  2. Thanks Julian. I will try these upgrades. I built a teak box that fits on the back of the bike.. My pit bulldog, about 60 pounds, rides everywhere with me, and I can leave the bike anywhere when i do some shopping etc. I will try to post the picture. I did notice something else about the existing fan. The blower seems to blow outside the bike (blowing hard off the left side of the bike) rather than onto the radiator or onto the motor. Maybe that’s normal, but it seems counter-intuitive. Could the fan be installed in reverse ? This sounds like a stupid question, but I seem to complain a lot more about the heat than anyone I know with the same bike. And today I found another ktm rider with a “heat canister” mounted on the muffler. He said it works great. At any rate, thanks for all the tips. Very helpful! Saludos,

    cid:7FE7582F-F9BF-4EF1-8F2A-DDD2E7589312 (here’s the photo)

    1. Hi Rick

      It’s your choice but I could never condone carrying a dog on a motorcycle, and a 60lb weight at the back of your bike will not help it perform at its best!
      As regards your fan, if it’s mounted behind the radiator, it will cool the bike by drawing cool air through the fins of the radiator – if it were to blow then it would be fighting against the incoming air when in motion. Blowing air onto the outside of a liquid cooled motor would have no effect whatsoever, so it’s not meant to be doing this.
      As regards your friend with the ‘heat canister’ on the muffler, I regret to say that this will have no effect whatsoever on cooling the engine. Exhaust gasses are extremely hot as they leave the engine, anything you do at the rear of the bike will not change that, although a less restrictive exhaust will allow them to exit the pipe quicker, but this only applies to a four-stroke as a two-stroke will need the expansion chamber. If the chamber he is talking about is one on the header pipe, a bit like a bulge in the pipe, this is a performance modification, not anything to do with cooling.
      (I could not see the photo!)



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