After driving the car hard for an extended period of time, i noticed the temperature was around 2/3 of the way up the gauge (usually sits at 1/2), im not so bothered about the overheating, because it was a tight course with low speed drifts, so was expected.
After cooling the engine and returning home, i checked the coolant level to find it needed topping up, around 100-200ml. I'm not sure what temperature reading would cause the coolant to boil, but is this normal behaviour given the circumstances?

 

Expected or not, these engines don't take any amount of overheating well, you should really be more careful about that. At this point, see if it continues to lose coolant, because the usual side effect of overheating is compromised water jacket seals. If you're lucky, you just lost what you lost, if you're not, you'll keep losing and have to rebuild the motor.

Just to give you an idea, the temp gauge is not super sensitive. I've been up to 225F (on the AccessPort) and the gauge was still perfectly middle. 225 is danger zone, so if you're gauge started moving, you were somewhat above that.

 

I was once at 230f (110*C) on the AP, the needle still didn't move.

 

Accessport is something i could really do with, im at the kind of mileage now where a rebuild is expected anyway, clearly the 13b is very susceptible to heat damage. FL22 boils at 270'F, but my coolant has been watered down over the years, and is 55k old so has likely lost some of its properties.