Supposedly it is supposed to, but I had one fitted for 10 years beneath the guard, and there is one on the LS mounted lower as well.

It's meant to make it easier for air to get to the overflow tank, but in practice it isn't a problem it purges itself anyway.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

thanks mate, I will stick it on the firewall,

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It does not matter. When BMC first used the expansion tank on the Morris 1100 they mounted it down low nearly straight behind the front bumper. The problem was that people didn't check it because they couldn't see it. So they started mounting them on the firewall next to the wiper motor where it could be seen. That was the reason to mount it high.
Air will always get out of the system into the tank because there is nowhere else it can go.
Mine is behind the front bumper but in the ten years I have owned the car I have never had to top it up.

So how does the expanded coolant make it back to the radiator? I thought the point of an expansion tank was not just to catch any coolant spat out, but to allow that to drain back into the radiator once it cooled... ?

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Simon

The adventures of an owner builder in the Tallarook Ranges

The coolant travels back up the hose. It has the pressure of the tank to push it back to the radiator.

Most modern cars have an overflow tank. It is an unpressurised tank.
The BMC expansion tank is not an overflow tank, it is under the same pressure as the radiator.

Of course How did I miss that?

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Simon

The adventures of an owner builder in the Tallarook Ranges