Sounds like you have air in the system , to bleed remove the rad cap ( when cold ) check coolant level in rad (to the base of the neck) , run the engine at tick over for 5 minutes or so ( must get hot enough to open thermostat ) . You should see the air coming out in the coolant in the form of bubbles forming.
When no more bubbles appear blip throttle a couple of times and stop , top up coolant if necessary and replace cap . Go for a ride and test , check coolant level ( in rad ) again when cold . Hopefully all will be well.