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I'm caught between a rock and a hard place. My 2010 KTM 250 XC won't stop peeing coolant out of the overflow tube. I've used 3 different radiator caps (two of the oem 1.8 bar caps and one CV4 2.0 bar) and it still continues to pee coolant as soon as the bike starts up. I just recently bought and installed brand new radiators [GPI on eBay for $88 (the seem fine just the welds are a bit crappy and you can see inside of the tubes where the metal from the welds drooped down but there are no blocks)] and silicone hoses (profactory hoses) thinking they were the problem since the old radiators were bent in like bananas. To my dismay that was apparently not the issue. I've had everything apart and looked at. Has brand new base gaskets, head gaskets, radiators, and radiator hoses. I've bled the radiators like the manual says and there are no bubbles like air leaking into the system or being in the system. The jetting is also perfect. The only thing I haven't changed out is the oem impeller in the water pump but it looks to be in great condition. Any ideas on how I can fix this problem before it gets worse? Also, has anyone else had this problem and figured out how to fix it?

I ride it in mostly tight 0-10 mph trails and also some 10-20 mph trails. 

Edited by MotoXRacer_19

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What are you running for coolant and what ratio to water? If you don't live in a cold climate and don't store your bike over the winter someplace that is susceptible to freezing temps, then run more water to your ratio, like 80% water. Water is a better coolant than antifreeze. 20% coolant is enough to keep the system lubed.

On top of that, treat the system with something like Red Line Water Wetter. You can pick up at any local auto parts.

I also recommend swapping the stock rubber impeller with the Aluminum unit. And with the impeller cover off, crank the engine over and make sure it's even turning.

Be sure the engine isn't running lean and that your jetting is right.

What premix ratio are you running? A richer premix ratio can help cool the engine. Like going from 60:1 to 50:1, tho not a drastic change, it's a little richer in fuel to help cool without being so much that it washes the cylinder walls.

 

 

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Its a possibility that you have a warped cylinder head. Or you may need a overflow because of slow technical riding. 

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Something is clearly not right. You should not have to use any additives (Water Wetter etc) in order for it to run at a normal temp. If you've done everything and checked all that you said you did, then of course change out the impeller (I would have done that already). If the bike starts overheating immediately I would make 100 percent sure that you are not getting water in the cylinder via a faulty head or O ring. You say your bike is perfectly jetted - what settings are you running?

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I use Engine Ice coolant which is mixed 50-50 and my premix ratio is 44:1. I checked the head and the entire cylinder and they're both 100% trued. I can't remember off the top of my head what my jetting settings are but i think i use a 170 main jet and I'm not too sure on the idle jet. I run it a little rich which shouldn't be the problem.

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You could check that your reed cage is not distorted and allowing air in from mid range up (causing serious overheating) and that the petals are closing correctly. Also, I take it when you refill the rads that you tip the bike over so that you get the air out of the left hand rad via the filler cap. Take it engine is timed correctly and your needle isn't too lean. Can't think of anything else at the mo you haven't covered

Edited by 7Tktm

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6 hours ago, MotoXRacer_19 said:

 

I ride it in mostly tight 0-10 mph trails and also some 10-20 mph trails. 

Well then that explains everything..

The cooling system works off airflow so the only thing u can do is force air through with an e fan or ride faster..

Waterless coolant will get hot but stay in the rads. If u don't want to use the Evans then put an overflow on.. Fixed..

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2 hours ago, 7Tktm said:

You could check that your reed cage is not distorted and allowing air in from mid range up (causing serious overheating ) and that the petals are closing correctly. Also, I take it when you refill the rads that you tip the bike over so that you get the air out of the left hand rad via the filler cap. Take it engine is timed correctly and your needle isn't too lean. Can't think of anything else at the mo you haven't covered

That's a good point, making sure the system is bled of air. A centrifugal pump like that of the KTMs impeller will not pump air.

Another good suggestion was making sure coolant passages are not blocked by mis-installed gaskets and such.

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Are you running the stock thermostat or did you do the thermostat bypass with the new hoses? I ride single track at super low speeds and my bike never overheats. I riding in 80˙f+ and 70% humidity. I use either Evans Waterless or Engine Ice at 100%. I also have the 2.0 bar radiator cap and Samco silicone hoses with thermostat bypass. Everything else is stock.

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6 hours ago, MotoXRacer_19 said:

I use Engine Ice coolant which is mixed 50-50 and my premix ratio is 44:1. I checked the head and the entire cylinder and they're both 100% trued. I can't remember off the top of my head what my jetting settings are but i think i use a 170 main jet and I'm not too sure on the idle jet. I run it a little rich which shouldn't be the problem.

How are you tuning the air screw?

What's your elevation?

Do you still have the original radiators? Measure the distance from the top of the orifice to the bottom sealing surface in the radiator neck that the cap goes into on both the old and new radiators. Make sure the new radiator isn't deeper. Make sure the sealing surface at the bottom of the neck is flat, not warped or has irregularities.

Edited by Trailryder42

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How much coolant are you losing each time? You could just be over filled and it's steaming out the extra. Happens to my bike whenever I top the coolant off.

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I measured all that to the original radiators and it's the same match up to the new ones. my air screw is 1 full turn out and my elevation is approximately 800 feet. 

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15 hours ago, Saint728 said:

Are you running the stock thermostat or did you do the thermostat bypass with the new hoses? I ride single track at super low speeds and my bike never overheats. I riding in 80˙f+ and 70% humidity. I use either Evans  Waterless or Engine Ice at 100%. I also have the 2.0 bar radiator cap and Samco silicone hoses with thermostat bypass. Everything else is stock.

the Thermostat is bypassed

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UPDATE

The water pump impeller is not spinning. It will spin with some force but if I push down on the kick starter it does not spin. Has this happened to anyone else and if so how did you fix it?

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Okay guys so I completely went through the bike. I replaced all cylinder and head gaskets, checked to see if both the head and the cylinder were true and weren't warped (they are true), put brand new piston rings on (the old ones were worn bad), the cylinder was rehoned to deglaze it, brand new oversized radiators, brand new cv4 2.0 bar. cap, brand new silicone radiator hoses, brand new checkpoint aluminum water pump impeller, bled the system, rejected the system (its running a tad rich) and the bike still pees antifreeze. :foul:. Any ideas on what could be the problem? 

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On 4/26/2017 at 11:21 AM, 7Tktm said:

You could check that your reed cage is not distorted and allowing air in from mid range up (causing serious overheating ) and that the petals are closing correctly. Also, I take it when you refill the rads that you tip the bike over so that you get the air out of the left hand rad via the filler cap. Take it engine is timed correctly and your needle isn't too lean. Can't think of anything else at the mo you haven't covered

2 strokes don't have timing

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When you say it pees out the the overflow as soon as you start it, I tend to think you are getting combustion or crankcase pressure is leaking into the cooling system.

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1 hour ago, ballane89 said:

2 strokes don't have timing

oh right cause two strokes don't have spark plugs. :banghead:

you say it spits out coolant as soon as you start it. either you are filling it right up to the radiator cap or your engine is pressurizing the cooling system.

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