Has coolant recently started peeing out the overflow tube on your dirt bike? Do you have to refill the radiator with fluid after every ride? If you’re lucky, it’s a cheap and simple fix. But if you choose to ignore the problem, it will only get worse. The two most common explanations for coolant coming out the overflow are: the bike is getting too hot, or there is too much pressure in the cooling system to hold the fluid.
The easiest problem to fix could be a faulty radiator cap. It may not be able to hold the pressure because it is worn or broken, allowing coolant to leak past it and out the overflow. Without spending any money, take a cap from another bike and put it on to see if that’s the problem. Ride around until the bike is warm, and if it doesn’t puke out any fluid, problem solved! If it does continue to spew coolant, then you know the radiator cap is not the problem.
Another common problem that will not only cause the bike to overheat, but will over-pressurize the system is a blown head gasket. It will bring engine temps up greatly, and possibly cause the coolant to boil over. Then the engine leaking compressed air into the system just blows it out the radiator because the cap cannot hold that much pressure. Before you install a new head gasket, though, you will want to check and make sure the cylinder and head are perfectly flat and not warped (usually caused by improperly torquing the bolts). If it is warped, you’ll want to take that to a machine shop and get it fixed. Putting a new gasket in with a warped cylinder/head will do you no good, so don’t ignore it!
Radiators don’t cool the engine by themselves. They NEED air to keep cool as well, so if they’re not getting any air-flow, it’s probably going to overheat the engine. A common problem that beginner and trail-riders have is riding too slow (More on this Here). Also, if a radiator is all bent up or many of the fins are twisted out of shape, that will reduce air-flow to the radiators. You can usually tweak most of the fins back if you’re careful, but it’s best to get a radiator fixed by a professional if it is badly bent or smashed. To increase air-flow even more, you can get a Vented Front Fender, or make one yourself if you have the patience.
A cause of overheating may be, although not as often, a broken impeller. If it’s cracked or part of it is broken off (yes, even one small piece) it won’t provide sufficient cooling to the bike. If none of the above are the problem, just pop off the water pump cover to see if the impeller is bad or if there’s corrosion. If there is damage, it’s probably going to be an expensive fix if you buy OEM, so you might as well buy a Boyesen Water Pump Kit for a little more and be done with it, for good.
If none of these are the solution to your dirt bike’s problem, then you have bigger issues. If that’s the case, check out my article Why Does My Dirt Bike Get So Hot?