Reasons for coolant to leak from breather hose?

[dizzyblonde]

expansion bottle thing...yes, if you take the seat off and unscrew the side panels! Can't see it otherwise.

just fill the expansion bottle to between min and max and keep an eye on it over a week or 2. Only top it up when it gets dry.

Providing the pressure cap is opening when hot and there are no leaks between the rad and header the radiator should be full unless it has blown excessive amounts of coolant out. This,as Chris says would probably be caused by in ingress of air through a water jacket or blown head gasket and by the symptoms described it is not this.Not trying to teach but you are using a 50/50 coolant mix.
Easy test for the rad cap is to put it in a bowl/pan of boiling water and see that it opens which it should do with 100 degrees C.
Fan kicking in and rad opening are two different temperatures.
In all honesty Diz PROVIDING YOU HAVE WATER IN THE HEADER it is nothing to worry about as I find level markings are not always accurate

[dizzyblonde]

Originally Posted by AndyBrad

just fill the expansion bottle to between min and max and keep an eye on it over a week or 2. Only top it up when it gets dry.

No, I shan't be filling that up. AS DT says it needs to find its own level first. I know the rads full, and putting more in, when its trying to push it out, is likely to make an already fragile radiator want to leak again.
I'm keeping an eye on it, and if it stops, then I'll make the necessary top ups. If it doesn't stop...then I shall be looking into clips etc, and also wondering if there is a blockage in the system. Which, surely if there was a blockage, it would run rather hot? Its currently running to what I'd expect, fan kicks in at 105, switches off once below, when riding around it runs at circa 83, so doesn't seem to be overheating. Obviously if I'm sat in traffic it creeps up to somewhere around 90 or more. I've yet to get it out on a mega hot day.

Ta for the chat DT

topping up the expansion tank (its not a sealed system) will not add aditional pressure to the rad. Its an open system so it will jsut push any excess out.

you want some in there so that you can (burp) the coolant pipes to get any air out and it can be replaced with coolant from the tank.