Since i, ve got the bike i always had to refill water every time i rode, but lately it started spilling more, the water is always refilled correctly,i do not know from where the water scapes, but theres always some in the cylinders head and all around, maybe thats only part of it when it is overcharged. Really i do not know, y checked the cylinder joint and they seem all right but i send to replace anyway.

maybe this thing can help to fix the problem,

the cooler is a special anti freeze (i know that it has nothing to do but maybe)

the bike was stopped for 5 to 10 years (i really dont know)

when opening the expansion tank while engine is on, it won't jump out and it is settling down.

when i fill the radiator by the expansion tank i unscrew radiator tap for the air to go away.

thank you

pd my bike is an aprilia climber 280 1994

May be just a defective radiator cap ???

thankyou but the problem is already solved when i changed head cylinder gasket,

jose