When they first start causing problems, they'll only bubble under full throttle, or if a turbo motor, only bubble under boost. They always get worse.
When you've popped your first hose, you'll look into it a bit more.
Problems like that always show up at the track rather than on the road.
Throwing in a bottle of chemiweld or similar will probably fix it in the short term, at least until you get something more permanent organised.
Unless of course it's not overheating and it's just your gauge that's playing up, but I suppose you'll hear it boiling when you stop.
Steve