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Where is my coolant going?

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I have a 2004 KDX200 and recently after every time I ride I notice my coolant in the reservoir goes down. In the last couple months I have actually had to refill it several times. There radiators are completely full and I have never smelled coolant nor over heated the bike. Is it possible I have a bad head gasket and the coolant is getting sucked into the cylinder and burned? Something similar happened on my truck and was causing it to run to lean. My local mechanic said that the head could need to be re-surfaced. Has this happened to any one else, any suggestions?

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A leaking head gasket is a possibilty, but there are others as well.

Have you changed the oil since you started noticing this? Did the oil look like chocolate milk? If so, the water pump seal is leaking.

You could have a bad radiator cap, allowing the bike to slowly lose coolant while you ride.

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The overflow tank on the KDX always ends up empty after a ride. It does seem to do the job of getting enough back into the rads for them to stay full though. I tried running without it and the rads would always be a hair low after a good ride. With the overflow tank on the rads will be full after a ride, regardless of weather there is any coolant in the overflow reservoir or not (almost always not).

There's an article floating around somewhere about heating the vent line outlet on the tank and bending it up on an angle, thereby routing the hose up higher which is supposed to help keep some coolant in there. The general feeling I got was that it simply gets sloshed out through the vent line.

If there's no water in the tranny oil, and no evidence of burning it, and most importantly the radiators themselves aren't low, then I wouldn't worry too much about it.

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+1 on looking at the tranny oil. Milky discoloration is a big clue if present.

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I change my oil frequently and have never noticed it being milky. I thought it could be the radiator cap, but wouldn't I smell it, or see it leaking? I do race the bike regularly so it does get ridden kinda hard but nothing to out of the ordinary. I guess it isn't that big of a deal, I will just make sure the radiators are full and keep an eye on the tank.

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I thought it could be the radiator cap, but wouldn't I smell it, or see it leaking?

If this is the case, it would only begin to leak when pressure is built up... most likely you are riding by then and more focused on other things in front of you. You would smell it once you come to a stop I would believe.

A new radiator cap is cheap, so it wouldn't be a huge investment if you went ahead and just got a new one.

If you are burning it (white smoke from the exhaust) sounds like a head gasket issue.

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Really, google a little bit on KDX coolant reservoir or coolant tank. You will see that most KDX owners report the same thing. That's why someone came up with the mod of re-routing the overflow tank vent hose, or putting a 1 way check valve in there to stop the coolant from running out of it through the vent line.

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Really, google a little bit on KDX coolant reservoir or coolant tank. You will see that most KDX owners report the same thing. That's why someone came up with the mod of re-routing the overflow tank vent hose, or putting a 1 way check valve in there to stop the coolant from running out of it through the vent line.
So does the coolant simply slosh out of the tank overflow while riding?

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So does the coolant simply slosh out of the tank overflow while riding?

That's how it seems, yes. I do know if you drop the bike on either side it runs out of there pretty quick like!

For the OP, if you need proof, just run with the overflow tank disconnected for a day or two. Your rads should get a few ounces low as a little gets lost from expansion, and then that's the level they stay at. If the rads get any lower then you must be loosing pressure in the cooling system from somewhere! Chokey pointed out all the places that can happen.

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