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spewing coolant out of radiator over flow

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i have an 07 kx 450 which spews antifreeze out of the overflow. The bike isnt over heating because the coolant that comes out doesnt even have to be hot. I have tried a couple differnt radiator caps and all the lines are clear... any ideas what might be causeing this??

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water pump, or head gasket, when it is running, feel different sections of the hoses too see if there hot OR take cap of and if the coolant moves around, it is the water pump.

other than that it would be head gasket, its still a overheating issue.

hope this helps:thumbsup:

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It's normal for a certain amount to be expelled. With off-road bikes and cars, they have a coolant recovery tank to catch it, then recirculate it back into the system when the motor cools down (motor warms up, pressure builds in the system, coolant expands, and leaves the rad. When the motor cools down, negative pressure sucks it back in). MX bikes don't have these, so when pressure builds, out the radiator and onto the ground it goes.

You just need to figure out if the amount your spitting out is within acceptable limits or not. Having someone with a cooling system pressure-checker take a look at it might be a good idea. It'll pressure test the system, and tell you if anything is abnormal.

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i have an 07 kx 450 which spews antifreeze out of the overflow. The bike isnt over heating because the coolant that comes out doesnt even have to be hot. I have tried a couple differnt radiator caps and all the lines are clear... any ideas what might be causeing this??

Got tired of this problem myself, so bought the optional 1.6 cap for a 2005 KX250 and added a coolant recovery tank from a CR250F. Here are some pics...

DSC00447.jpg?t=1230704896

DSC00446.jpg?t=1230704958

I had to make two small brackets, but the installation is clean and all coolant issues are resolved. Bottle fills up while riding, and returns when cool.

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water pump, or head gasket, when it is running, feel different sections of the hoses too see if there hot OR take cap of and if the coolant moves around, it is the water pump.
Evan1 might be on to something. I often ride in some heat (up to 33C) and on relatively slow MX tracks too (2nd and 3rd gear only). But my bike has never over heated. Always my coolant ends up about 1 inch below the cap, so some overflows if freshly filled. But the engine doesn't keep loosing coolant. OK I'm not doing tight "woods" speeds, but it gets pretty hot. If I stop the bike and my heart rate is up, I want to get of the thing in a matter of seconds. Stock cap. Basic coolant (1/3rd glycol). My jetting is good - the engine rips from 2000 to 11000rpm.

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I would not put a higher pressure cap on , the system is designed to run at a certain pressure and release excess pressure when needed .

I have done the same as Kxvett with a overflow bottle but used the one off the Yamaha WR , bolts onto the rear fender bolt and needs some slight trimming of the plastics . Works very well .

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Got tired of this problem myself, so bought the optional 1.6 cap for a 2005 KX250 and added a coolant recovery tank from a CR250F. Here are some pics...

I had to make two small brackets, but the installation is clean and all coolant issues are resolved. Bottle fills up while riding, and returns when cool.

That's great!! I switched from a WR426 to '08 KX450 and I miss the overflow tank. I ride a lot of single track in the Arizona HOT desert. I was looking at getting one from a KLX, but this one looks much smaller. Thanks for the great idea!!!! :thinking:

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Riding last weekend, a couple of guys were looking at my bike from the rear and finally asked if I was riding a KX or KLX. The rest of us just starting laughing. Fooled another one...

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How fast is this happening? Is it like, start the bike then instant spewage or no? Are you moving when this happens?

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