Hubble bubble toil and trouble - boiling coolant on NC30

[banoffee]

In traffic on these very hot days here the NC has got pretty hot, not far off the red but not on it. While there the coolant expansion tank is visibly and audibly bubbling with some dribbing out of the overflow.

When riding along at speed it settles to about 90/95 or so.

Normal?

[matt_nc30]

Mine always goes near the red after a few mins in stop start traffic.

Seems to take an age to get up to temp from cold, but gets too hot too quickly

[RobTriskele]

Mine does it aswell but I cannot say if its normal

[Spoonman]

Coolant doesn't boil until well over 100C so the source of any bubbles is gas getting into jacket.

I know it's bad news, but I'd be checking the head gaskets - may not be quite gone, but could be blowing a bit.

Best to catch it before coolant starts getting into the cyclinder when she's cold.