Hello there, I have just purchased a 2014 st300 with a cracked radiator. I have replaced this with a brand new item filled her up with new coolant. When testing the bike after a few minutes of riding it got very hot and coolant started to bubble out of the ‘release valve’?? A little brass thing at the top next to the filler cap? Just wondering what people’s thoughts are?

 

thanks John

It's the pressure relief valve letting excess pressure out of the rad.If it's getting really hot it might be air locked,is there a little bolt in the top of the head near the radiator hose which you need to loosen when you fill it ,there was on my Gasgas and is on my TRS.Splatshop will tell you,give them a call

Or the previous owner ran it low on coolant via the bad rad and cooked the head gasket seals?

Fan are working fine?

If all the components and parts are intact and working as they should and your still having the problems, those '14-'15 Factory 300's have an older  thread or two on this site with owners having problems with them from brand new.. Best of luck

If radiator was full filled, some has to escape there

Fan and head gasket and water pump where nackered, fixed it then swapped for a 2020 4rt??