When working properly, the cooling system on a dirt bike does an excellent job of efficiently keeping the engine cool and this is true whether the motorcycle is air cooled or liquid cooled although for a liquid cooled dirt bike, there several different components which all work together to provide efficient and relatively maintenance free cooling performance, yet these components do need routine maintenance and upkeep which we're going to go over below.
Whether the bike is air cooled or liquid cooled, a dirt bike demands periodic attention be brought towards the cooling system in order to keep the engine cooling properly. Routine maintenance can frequently prevent overheating or other engine problems, and this is true whether you're riding casually, or you're racing motocross. Pounding down an off-road trail or course, or if you're hucking gaps and working on new FMX tricks, the cooling system can't be neglected.
On liquid cooled dirt bikes, there's a lot that's going on while keeping the bike cool in the heat of battle whereas an air cooled machine relies on cooling fins which are integral to the cylinder and cylinder head to dissipate heat away from the engine, a liquid cooled bike uses multiple parts all working together to provide a much more efficient and quiet running engine.
The Basics of keeping a liquid cooled dirt bike cool:
(In addition to the anti-freeze regulating freezing and boiling temperatures)
Bottom line is that by maintaining the health of the cooling system components such as the radiator, cooling passages / jackets, hoses and impeller should leave you with one more way to get another advantage and have maximum cooling performance so here we go...
As recommended in our article on washing a dirt bike, it's best when cleaning the dirt bike to use a lower pressure of water than that of a power washer around the radiators otherwise the radiator's core or tank seals could be damaged and have a resultant leak.
Beginning with the Exterior: It's really no secret that a liquid cooled dirt bike has a radiator or radiators placed in a rather vulnerable position being just behind the front wheel where flying rocks, roost and incoming sticks and branches are the norm and can puncture a radiator or cause a leak, so be sure after each ride to visually inspect the radiator's condition while also ensuring that the front of the radiator(s) are not covered or blocked with mud, leaves or any other debris that could obstruct air flow.
Additionally, you'll want to inspect the remainder of the cooling system looking for leaks which sometimes become evident during a ride by a smell of anti-freeze, as well as checking the condition of hoses for any irregularities such as bulging or other damage.
Once the engine has cooled it's also wise to check the coolant level as you want this to always remain full and clean with fresh coolant. If the coolant is constantly low, there may be an internal or external leak that will need to be addressed although if there is not an evident leak, you may find success in simply replacing the radiator cap.
If you have noticed coolant pooling on the ground under the motorcycle, or if the oil is looking milky, it's highly likely that the water pump seals are worn out and the cooling system is in need of service such as replacement of the water pump shaft, seals and bearing although if the oil is milky, be sure to change the oil at this time as well.
With an engine that has cooled to a point where the radiator and engine can be comfortably touched and the hoses feel as if they are not under pressure as can be felt by gently squeezing the hose with your fingers, the radiator cap can be removed for inspection of the engine's coolant.
With the radiator cap removed, you'll want to look into the filler neck at the condition and level of the coolant. If the coolant looks like it did when it was poured in then it's probably alright, although if the coolant has not been changed in quite some time, you may want to see the article below on changing the coolant as the coolant does break down over time and it's anti-corrosive and cooling properties do become diminished over time.
If the coolant doesn't look clean, and you notice any dark substances such as oil or black residue floating in the water, this may indicate a leaking head gasket or water pump seal which will need to be addressed. If the coolant looks a reddish brown, this may indicate that the cooling system has not been cared for and is in need of service.
With the cap off, it's also a good time to check the flow of the coolant and this can be done with the coolant level filled to just above the cores of the radiator and then starting the motorcycle and revving the engine slightly while looking into the filler neck at which time you should notice the coolant circulating
It's important to remember that engine coolant has properties at work which help regulate the boiling and freezing points of the engine's coolant, as well as the coolant possessing other properties to help prevent oxidation and corrosion of high dollar aluminum parts from within.
Additionally, considering that coolant breaks down, the coolant should be replaced periodically per the manufacturers recommendations which can be found in a factory service manual specific to the motorcycle being serviced, or on the label which accompanied the coolant that is currently being used.Once you're committed to replacing the coolant here's how:
When refilling the engine coolant, be sure to inspect the motorcycle for any type of bleeder on the cylinder head or radiator. If there is a bleeder, it's critical that the trapped air is allowed to escape during filling otherwise the engine will likely develop an overheating condition caused by trapped air.
Once the coolant level is full, and any trapped air has been released, replace the radiator cap and you're ready to go.
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