Been out in the loco enjoying the sun, but the other day I was caught in a bit of traffic and saw that the water temp was rising towards 120 C so pulled over to let things cool down.
So how hot is too hot and what can be done to keep water temp down. (apart from only driving on cold days)

Bigger fan, or avoid traffic

Does your fan work? I'd check it. Temperatures over 105° wold concern me if I was driving.

My car doesn't need the fan when moving, even when driving hard on a really hot day. Only when idling does the temperature really rise and the fan cools it down quite quickly at around 100°.

I have a manual overide switch for the fan so it can be switched in traffic even before the temp rises.

May be worth checking the plumbing arrangement.
Assuming it's a Kawasaki, I've plumbed mine as per Ben Marriott's diagram and even without a fan, it can sit for ages without going above 100 C
Diagram is at

linky