Bad radiator cap????

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#1
Could a bad radiator cap be at fault for coolant comign out of vent hose, occationally? It seems to only do it while the bike is running in the rpm's or going over jumps. I just rebuilt the bike any help is apprecciated!
 

Canadian Dave

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#2
It's not uncommon to have a little coolant leak from the system if you fill the rads completely full of coolant. As the system heats up the coolant expands and takes up more space. After a couple rides enough coolant should leak out that when the engine is at running temp the level is to max point and it stops leaking. If you fill the system does it stop leaking after a couple rides or does it continue to expel coolant week after week?

David
 
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#3
this is a good question. I don;'t know becuase every time i check it, it is low so i just fill it up. but it never used to get that low until i rebuilt my engine. then every since then it goes down, below the lip of the rad.
 
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#4
Yes it is possible that the spring or seal on the rad cap are sus & letting coolant out more readily than they were designed to.

But the usual reason is that the head gasket is leaking & is pressurising the system pushing coolant out. A leak down tester would provide a test, sadly most shops do not have them.

As you indicate this has started after the rebuild it tends to suggest this. Did you replace the headgasket for new? & did you check the head for straightness?
 
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#6
Well replacing the cap is cheap & I hope this solves your problem but if you are still losing noticeable amounts of water you will have to investigate further.

Good luck
 

canyncarvr

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#7
You said out the vent hose, right?

I put this in the same group as, 'my bike pees gas when it's on the side stand'.

Yep!

I used to put coolant in my reservoir tank every ride. After every ride, it would be low, and coolant evidently had come out the vent hose. I stopped putting coolant in...just checked the rad level.

The rad level didn't change in 1/2 dz. rides with the reservoir empty!

I don't see that you mention if your rad level is staying up or not. If it is, and the coolant is coming from the tank..don't worry about it.

...............
Sorry! Completely missed the '250' part.

<delete> <delete> <delete>!!!
 
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dirt bike dave

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#8
C'Carver - the KDX250 does not have an overflow tank.

I agree with C'Dave that it could well be normal expansion of the coolant. One way to check is after the bike cools completely, measure how much fluid is required to fill up the radiator. If it is the same after 2 or 3 rides in a row, is probably just normal expansion and you don't need to replace the coolant that is just going to spill out the vent tube anyway.