I bought a brand new Aprilia Pegaso Trail a few years ago.
As i had a trip planned already, I took a taxi to the shop, where they had mounted all the bags and stuff already, put all my gear on it and went to the trip. Through muddy / gravel roads of course. After 100km, overheat warning came on. After I shut down the engine, I noticed i've lost all my coolant. It all came out via overflow pipe or something (dont know how to call that pipe on radiator). Didn't have any coolant as i was in the middle of nowhere, we used drinking water (with bubbles) to get me out of there. Drove back trhough normal roads, with high gear and low revs, to keep the engine cool. Took the bike back to the shop the same day. My trip was ruined, i was tired and the salesman was surprised.

Next day they called me they ordered a new waterpump.
Then a week later they told me they replaced all coolant-related stuff.
2 weeks later no news. Called the shop and asked for money back. Got the money back (all of it), went to Yamaha centre, bought a new XT660 :P

Few months later i had to buy an oil filter to another aprilia so I had to visit the shop. Asked, what happened to the Pegaso. The salesman went a bit red - a week after i returned the bike, they accidentally changed (during some testing) the radiator filler cap from my bike to another. The fault then moved from one bike to another. So there it was ;)

I don't blame tha Aprilia centre, NOBODY ever thought that the simplest thing could go wrong on a brand new bike... That's why nobody ever tried to replace that.

well i got the cap it stopped leaking ,but it started leaking with the pump so ive changed all the seals in the pump and now its fine :smile[2]:

Please can you give me the date stamped on your leaking radiator cap, thanks.

I've just developed the exact same issue on my 07 XTX, the radiator cap was leaking but not massively. When I took the rad cap stoppers off, let the bike idle for about 2 minutes, then it gushed out. The coolant is flowing with no other leaks, as far as I can see that is. The overheating light hasn't come on yet and neither has the fan. I've checked the rubber seals and they look OK but then again I've really no idea!! My question is, did replacing the rad cap solve your issue?

I've posted this before but just in case anyone does have Rad issues. Try these guys first before you splash out on a new one. They do good work and to be honest good people like this are hard to find... I've used them to sort a rad leak on another bike. They pressure test and go from there and aluminium rads are not a problem.... hope this helps..

http://www.felthamradiators.co.uk/

The water will poor out if the cap is left off, the radiator cap is there apply pressure to the cooling system which raises the boiling point of the cooling system to around 110 degrees C. The XT660 fan only kicks in at 105C so if the cap is leaking the water will poor out & the fans won't run due to the pressure loss & the water will boil at 100 degrees C.

Yes my new radiator cap fixed my coolant leaking problem.