bike developed coolant-ary incontinence (curvy)

BTW Dabteacake, many modern caps are two way valves, they let excess pressure out and atmospheric pressure in.

Originally Posted by -Ralph-

OK - One possible theory is - When you switch off your engine coolant flow stops, if the engine block is very hot it can boil. That expands and turns to steam and the extra pressure has to go somwhere. That somewhere should be the radiator cap, but if it cant get out there it finds the only other place to bubble out, which is your expansion bottle. As the steam comes up the pipe work to the expansion bottle, it pushes coolant up that pipework raising the coolant level in the bottle. The bottle has an overflow pipe and thats where the incontinence comes from.

Someone might think you had experienced this firsthand?

Originally Posted by ravingdavis

Someone might think you had experienced this firsthand?

Indeed, but that wasn't a curvy, and I've never had a curvy, so it's just a theory. Still doesn't explain everything in the OP. If the hoses are indeed under constant pressure and leaking from the jubilee clips as the OP suggests (that's just the conclusion he's reached, it doesn't mean it's right) then that pressure is getting trapped somewhere it shouldn't and isn't finding it's way to the expansion bottle. I've seen more than enough threads where the conclusion doesn't correlate to the symptoms, to know to not always take the info in the OP as gospel.

it doesn't work exactly as ralph described.
the cap has a release valve which stands in the way between the cooling system and expansion bottle. so if the said valve was stuck, system would remain pressurised, possibly causing the hoses to weep at the clamps.
i just don't see how the cap valve could fail to a permainently closed state. it's just a plug on a spring, easy enough to compress using fingers.

Originally Posted by m`baubz

it doesn't work exactly as ralph described.
the cap has a release valve which stands in the way between the cooling system and expansion bottle

Not sure why that's different to what I already described, if it reads as being different then I've not explained it very well. Hot gas will escape though the cap, fluid will overflow to the expansion tank. Sometimes though if the cap is a bit sticky the valve doesn't open properly and the expansion bottle is the only way out.

Originally Posted by m`baubz

so if the said valve was stuck, system would remain pressurised, possibly causing the hoses to weep at the clamps

Well that's exactly what your describing, which is why everyone is telling you to check your radiator cap.

Originally Posted by m`baubz

i just don't see how the cap valve could fail to a permanently closed state it's just a plug on a spring, easy enough to compress using fingers

It's a simple mechanism but it can still seize up like any other. You said it first happened after a long run, so it's possible your bike hadn't got hot enough to open the cap for a good while, then when it tried to the valve was seized in it's normal closed position.

Have you had it off and looked at it? I think it should be opening at about 1 bar of pressure.

A new one is about 25 quid.

just to wrap up the thread:
did a thorough check of the plumbing the other day and found the cause of the problem:
the thin hose leading to the expansion tank was blocked with white crap. cleaned that,
flushed expansion tank with a few litres of water, tightened hose clamps and all should
be ok now.
so yeah, change your coolant regularly and don't use tap water (not that i did, but someone
before might have).