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radiator overflow leaking

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My bike is leaking out of the overflow tube every time I ride it. The coolant now is probably an inch below the radiator fins and it still leaks. Is something major wrong or could it be the radiator cap is not holding the coolant in? Where is the overflow coolant supposed to go when it runs out of the tube? I have a ktm 125

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1) It could be a blown head gasket causing the excessive pressure in the coolant system, or 2) your radiator cap needs to be replaced.

Fill your radiator back up and start the bike , remove the radiator cap while the radiators are still cool and watch for air bubbles rising up at a pretty rapid rate, if you see a lot of air bubbles then it's most likely a blown head gasket. If you see very little to no air bubbles, then it's probably your radiator cap.

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do you ride extremely slow, i know on race thumpers if you ride very slow theres no airflow to the rads causing the coolant to expand and overflow

make sure you get the airbubbles out if you drained the coolant, somebike have little bolts on the head while others you leave the cap off and run the bike for a few minutes

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I ride at a medium/fast pace. I did take the cap off one time when the bike was warm at when I first pulled of the cap there were some bubbles and radiator fluid seemed to be in the overflow area past the pressure seal. I'm not sure if the fluid shot up when I released the cap or if it was already there.

So I'll fill the coolant back up and start it without the radiator cap on. How long will it take for the bike to fully warm up where the coolant is circulating well? Anybody else have any ideas what the problem could be?

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I ride at a medium/fast pace. I did take the cap off one time when the bike was warm at when I first pulled of the cap there were some bubbles and radiator fluid seemed to be in the overflow area past the pressure seal. I'm not sure if the fluid shot up when I released the cap or if it was already there.

So I'll fill the coolant back up and start it without the radiator cap on. How long will it take for the bike to fully warm up where the coolant is circulating well? Anybody else have any ideas what the problem could be?

It can only be two things rad cap or head gasket. Do you have a oem or after market head gasket?

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I have a moose head gasket but I just bought a new radiator cap, I"m going to see if that fixes the leaking overflow tube

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I have a moose head gasket but I just bought a new radiator cap, I"m going to see if that fixes the leaking overflow tube

Next time you change the top end Buy an oem head gasket. Cheap aftermarket head gaskets always leak prematurely. At least my experiances with them. Hopefully its a weak spring in the rad cap. If that does not fix it change the head gasket.

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So if the head gasket is leaking could this also be the reason for low compression (135 psi) and lack of power?

Oh yeh; I would change the top end with 135 psi, you should be in the 150 -170 range. Remember coolant destroy's bearings, check your crank sevice limitations. You never want to let a leaking head gasket go to long it could end up costing alot of $$$. I know: when your bike isn't running correctly, its not the funest thing to go through. At the end of the day they are machanical experiances that in the future can help you trouble shoot problems. Best of luck to you

Edited by mxn4life

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I'm planning on doing the top end in a few weeks.

So I added about 2-3 ounces of coolant (not as much as I thought it needed) Started the bike, let it warm up for about 3-4 minutes with the radiator cap off and observed it. At idle there didn't seem to be really any bubbles. The coolant was flowing very slowly and that's about it. When I revved the bike, the coolant ran much faster and there were some tiny air bubbles but nothing excessive, I think. It was more foamy then anything. I really don't have anything to compare it to so I'm not really sure. I took some photos, maybe you guys can help.

This one is when the bike is about 3/4 throttle.

p><p><img src=[/img]

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Why does that coolant look so thick in the first photo?

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I was revving it and the coolant is shooting out of the tube against the wall. Its just foamy, I think.

I would say that it's a leaking head gasket, and your lucky

1) Its a small leak

2) the presure is pushing into the cooling system instead of the coolant leeking into your crank pitting your bearings. Get a piston orderd and an oem head gasket and don't run it any more. Hope this helps

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Cam I just replace the head gasket for now? The top end was just rebuilt and has only about 25 hours on it. So the leaking gasket would also explain the low compression.

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Cam I just replace the head gasket for now? The top end was just rebuilt and has only about 25 hours on it. So the leaking gasket would also explain the low compression.

You don't need a new piston, but you do need new rings the get the compression up between 150-170 range. what kind of piston do you have in it? Wiseco rings are 35 bucks, an oem head gasket is around 12 bucks. not to bad

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I have a Wiseco piston. So I need both the inner and outer head gasket rings and wiseco rings?

Correct you need the small and large ruber O rings they cost 8$ a piece for the top. Since your pulling the jug off To install new rings, you should replace your base gasket as well witch is 6$.

Its a sx 125 right. What year is it? I can get you part #'s so its a little easer.

Your going to have to call wiseco directly to get the p rings. let me know if I can help.

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Correct you need the small and large ruber O rings they cost 8$ a piece for the top. Since your pulling the jug off To install new rings, you should replace your base gasket as well witch is 6$.

Its a sx 125 right. What year is it? I can get you part #'s so its a little easer.

Your going to have to call wiseco directly to get the p rings. let me know if I can help.

Its a 2004 ktm 125 sx. I replaced the radiator cap and the leaking seems to have stopped. I still want to replace the O rings and base gasket your talking about. Anything you can do would greatly be appreciated bro. I'm new to this whole scene and don't know where/what to buy. Would I be able to replace these myself? thanks

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