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I replaced my coolant overflow tank. I was surprised to realize hose going into the tank from the radiator and one hose going to the ground. Am I correct in thinking once the coolant is in the tank, there is no way for it to return to the system without taking the tank off the bike?

If that's so, it almost easier to just top the radiators off with fresh coolant once you're home.

So I was thinking of using it as an extra fuel tank. It would be fairly easy to route the hose to the exsisting fuel line and put a Y and an on/off valve inline. That way, if you need more fuel, after your reserve runs out, just open the valve and use that tank. You could even see the fuel level and how close to being stranded you actually are.

Anyone ever done this?

The downward hose is the overflow, in the event that you overfill and the coolant expands to the capacity of the overflow tank, it will run out the overflow hose. The single hose from the radiator to the tank passes coolant both ways. As the coolant in the radiators expands, it will flow through the tube out to the overflow tank. Once the radiators cool and the level drops in the radiators, the coolant is sucked back into the radiators through the same hose.

Could it be sucked back in? I thought in order for it to leave the radiator it would have to blow past the cap with the pressure seal. I didn't think g it could get sucked back past the cap because it is pressurized.

morganid wrote:Could it be sucked back in? I thought in order for it to leave the radiator it would have to blow past the cap with the pressure seal. I didn't think g it could get sucked back past the cap because it is pressurized.

Yes, it can get sucked back in, just like every car ever made with a coolant tank since the late sixties.

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I understand cars/trucks have an overflow tank that works this way. I don't know what type of valve or gate is used to keep the system under pressure while allowing coolant to re-enter the system after the motor cools.

I thought that in a dirt bike radiator, if it got hot enough expell coolant, it would create a vacuum on the radiator when it cooled down. But I figured it would suck the cap down tighter which wouldn't allow anything to enter the system.

Is this not what happens? Does the vacuum suck the expelled coolant back in the system past the cap?

morganid wrote: I don't know what type of valve or gate is used to keep the system under pressure while allowing coolant to re-enter the system after the motor cools.

Does the vacuum suck the expelled coolant back in the system past the cap?

Your first statement is flawed. Coolant is not sucked in while the system is under pressure.

In a recovery type system, the cap is referred to as a 'double seal' cap. There is a vacuum valve in the center of the cap to allow the coolant to be sucked back in once the system cools off and creates a vacuum.

Ok. That makes sense. I guess I've never really looked into how it works. Thanks.