Reply To: GV125 S — Engine issue?
Adding to simon’s comments , check the “Caps” of the radiator and “reservoir tank” , for any damage , heat can sometimes “evporate” liquids although coolant has a high boiling point , it is worth checking since you said you heard some “hissing” on the bike.
On old GV125 (oil cooler model) in summer time , hissing noise was fuel tank cap venting to atmosphere to avoid lock up , this was normal. (if i shook a tank on a hot day, i will hear hiss from a fuel cap)
Use “Motul FACTORY LINE” coolant for the bike, I always use it on my own bikes.