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robby111

home made coolant overflow

13 posts in this topic

I rigged up my own overflow but when the radiator did boil over the coolant went into the tank but wouldn't syphon back. So the tank would just fill up until coolant would leak out of the top tube. Does the tank need to be higher then the radiator?

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If the hose goes in from the top then it needs to go in as close to the bottom of the tank as possible. Otherwise mount it on the bottom of the tank.

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The hose coming from the radiator goes in at the bottom. The overflow hose is on top.

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Then it should work. Check the underside of the radiator cap and see if the metal flap valve thingy is free to open and close.

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It isn't going to syphon the coolant back in. Think about what is happening. Under the cap there is a rubber gasket with a spring on top of it pushing down creating a seal, this is a one way valve. When the pressure in the radiator gets to be enough to overcome the pressure of the spring, the seal lifts up to release some pressure, and some coolant goes around this gasket and out the overflow tube. When some of the pressure in the radiator is releaved, the spring force takes over and the gasket is sealed again. When it cools down the pressure in the radiator becomes negative, but the gasket in the cap prevents any coolant from being sucked back into the system. Without changing something in the system, it will not suck the coolant back in.

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Then it should work. Check the underside of the radiator cap and see if the metal flap valve thingy is free to open and close.

The thing with this spring? The spring moves fine if thats what your talking about.

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It isn't going to syphon the coolant back in. Think about what is happening. Under the cap there is a rubber gasket with a spring on top of it pushing down creating a seal, this is a one way valve. When the pressure in the radiator gets to be enough to overcome the pressure of the spring, the seal lifts up to release some pressure, and some coolant goes around this gasket and out the overflow tube. When some of the pressure in the radiator is releaved, the spring force takes over and the gasket is sealed again. When it cools down the pressure in the radiator becomes negative, but the gasket in the cap prevents any coolant from being sucked back into the system. Without changing something in the system, it will not suck the coolant back in.

On my WR250 it would suck the coolant back in. So how do I make my CR do this?

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Not the spring. It is in the center of the rubber gasket part. Small round and metal. You should be able to catch a fingernail under it and pop it open.

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Not the spring. It is in the center of the rubber gasket part. Small round and metal. You should be able to catch a fingernail under it and pop it open.

Yes, many caps do have an inner one way valve to releave the vacuum created. These caps will allow you to suck fluid back in. Check and see if your cap has this.

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It isn't going to syphon the coolant back in. Think about what is happening. Under the cap there is a rubber gasket with a spring on top of it pushing down creating a seal, this is a one way valve. When the pressure in the radiator gets to be enough to overcome the pressure of the spring, the seal lifts up to release some pressure, and some coolant goes around this gasket and out the overflow tube. When some of the pressure in the radiator is releaved, the spring force takes over and the gasket is sealed again. When it cools down the pressure in the radiator becomes negative, but the gasket in the cap prevents any coolant from being sucked back into the system. Without changing something in the system, it will not suck the coolant back in.
I have had a small bottle zip tied to my 02 520 exc KTM for 5 years NOW and it works great, Ran the tube in the top and sealed tight with silocone from the radiator overflow run the tube 1/4 inch from the bottom and then fil the bottle up with fluid 1/2 above tube it will suck the fluid back in before the cap de-pressureizes..Works great..I did this after my bike boiling over in a hare schramble in muddy conditions naver had a issue after installing the tank..

Here is a photo look close and you can see the zip-tied bottle..I am not Being smart but I know it works has Been for me for years..I might be the way the KTM caps are set up..

DSC01856.jpg

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Looking up parts, I'm going to guess that the 01 CR's did not come with caps with the internal one way valve to allow it. The caps for those bikes list for more than half the price of the Yamaha caps, which have the one way valve in the middle. I know OEM Honda parts are normally on par, if not a little more than OEM Yamaha parts, so this makes me think the caps are simpler.

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Is it OK for a bike to overheat all the time? Would a higher pressure rated cap fix/help/make it worse? Just curious.

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On my WR250 it would suck the coolant back in. So how do I make my CR do this?

Buy a WR one from the Yammie agents & fit it, maybe you can pick up a used one from a wrecked bike.

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