Flushing the radiator on your dirt bike should be part of your regularly scheduled maintenance and is essential to getting the most miles out of the engine.
Draining, flushing and adding coolant sounds like a job for a professional mechanic but, in fact, it's one of the easiest service tasks you can do. Plus you only have to do it once a year or so. (Always check owner's manual.) It is like changing the oil, something that you can do on your own. However, a radiator flush or even just simple coolant change does take some time as you'll idle the engine and then have to wait for it to cool down several times, so plan accordingly.
Since you're playing with liquid, plan for the mess, hope for the best. Therefore, grab lots of disposable towels and/or the blue shop paper towels. As for the rest, you'll need:
Don't change the coolant on a hot bike. Be sure the drain pan sits low enough under the crankcase to catch the used coolant with room for you to unscrew the drain plug. Use the socket wrench for the drain plug. (Depending on the model it might be the Allen wrench). The drain plug is conveniently on the right side near the front of the bike next to the clutch housing.
The bolt you're removing is actually on the water pump housing. There is a copper sealing washer under the bolt head. DON'T LOSE IT. Or go fishing for it later in the pan of used coolant. (Since copper is not magnetic one of those magnetic pick-up tools is useless.) Remove the bolt with the drain pan underneath to catch the dripping liquid. Once you've removed the bolt don't expect the old coolant to stream out. It might even "chug" like when you turn a milk jug of water completely upside down and remove the cap. To get the maximum flow you need to open the radiator cap. (Don't do this before removing the drain plug or you'll guarantee yourself a mess.)
If it's your first time you might need to guess where to place the drain pan so it catches the stream of liquid but place the pan in correlation to the angle of the flow spout. Be prepared to move the pan if the stream misses the pan. This is where a second person could be useful as you unplug the radiator cap your helper can assure the pan catches the old coolant.
Once drained, put the drain plug back on and add your flush, using the funnel, into what is actually called a Bung Hole (where you removed the radiator cap). Myler's Miracle Flush and Super Coolant Combo is a solid choice.
Mechanic's Note: If you change the coolant regularly using a non-corrosive formula then it's likely you'll never need to flush the system. Conversely, if you're changing from a standard coolant to a premium coolant it's best to flush the radiator. (To be safe, if you're changing coolant brands, flush the system.) Use a dirt bike (or powersports) specific coolant not one for automobiles. Excellent dirt bike coolants include:
If you live in an area where temperatures get below freezing you want to use an anti-freeze/coolant for your dirt bike.
Continuing, pop the radiator cap on the Bung Hole, of course tighten, and start the engine. Run the bike until it gets to operating temperature then shut off. Wait until it cools down and drain the radiator flush using the above instructions.
Now you're ready for the new coolant. Put the drain plug back in and since dirt bikes are all about proper torque specs refer to your manual for proper tightness. Add your new coolant into the Bung Hole. Don't overfill. Place the radiator cap on, start the engine and let run until it reaches normal operating temperatures. Let it cool down. Add additional coolant as needed.
Now go ride and change the coolant next year.
Written By: AndrewT