Thermostat just installed (aftermarket tridon) now coolant problems

[Dutchy]

Just installed new tridon thermostat in my ST1100A as it was not moving temperature needle more than 2-3mm, old thermo was stuck open..
Refilled radiator with new coolant, started bike up with radiator cap off, after approx 5 - 10 minutes all looking good, needle up approx half way and fans came on, when suddenly coolant started pouring out of radiator top..
Switched off motor and all of the coolant shot out like a fountain ?
Where am i going wrong ?

[Brock]

You shouldnt run with the cap off, and when you turned the engine off the water (coolant) boiled. When the fans come on , the engineis very hot. On normal operation when moving, the temp needle is only a little over the cold mark.

[Dutchy]

Ok, thanks Brock,
First time I tried it with cap on it pushed all the coolant out of the reserve bottle onto the floor, so I am only guessing but could there be a bit of air in there somewhere to cause that !
Just tried for third time as per service manual, let it run cap off for a couple of minutes, gave her a few revs, coolant had some bubbles, topped it back up, done same again, put cap on and let it run for 5 minutes and as you said needle only went up small way and stayed there.. so i think all is good.
Thanks again mate, i havn't met you as yet, but certainly owe you a few cool ones when i do..

[Brock]

owe you a few cool ones when i do..

Only have to get to WA..