Steaming radiator cap

[scubasteve]

hi guys,
took the bike out for a good run today as finally the weather has changed for us. Unfortunately my fun was cut short after an hour or so as when i pulled up at a petrol station and noticed there was steam rising from the radiator cap. It seemed to be coming from around the hole base of the cap. I Had been pushing it a bit hard and the weather was quite hot but still, this obviously shouldn't be happening. I was around 25miles from home so decided id let it cool down for 15 mins then go for it. Took it steady on the way home keeping temp gauge bellow 90 and had no problems at all. when i got home i looked at the cap and it wasn't steaming or anything. Seems to me like its a faulty radiator cap that's only leaking when the bike gets really warm but thought id ask your opinions and see if anyone's had this issue themselves.

[nazzurro_19]

Pressure can cause the rad cap to lift, is there too much fluid in your radiator maybe? Or/and over flow

[CMSMJ1]

Have you got an overflow bottle fitted?

[scubasteve]

Yes, I do have an overflow bottle

[scubasteve]

Checked my overflow bottle this morning when the bike was cold and the coolant is just above the minimum line. I then took the rad cap off and the level in the radiator itself was about a inch and a half from the top. Just a thought, but should the coolant in the overflow bottle not backfeed into the radiator and top it back up? When I checked the level in the rad the other day it was at the very top.

[Lane]

If the seal on the radiator cap isn't sealing properly, it cannot create the vacuum required once cooled to suck the coolant back into the radiator.

As well as venting cooling system pressure to atmosphere and losing it's anti boil properties.

Replace the cap.