Just as an add on to the initial post, I just got a OBD2 reader that gives 'live' sensor readings and today, a warmish afternoon, the coolant temp was showing (on the reader) from 75c at a low throttle 30mph going up to 91c in a traffic jam ? The cooling fan comes on and goes off at what seems like normal regularity. does this sound normal

also as I am currently running on water only would this make the car run hotter or cooler than with the recommended 50/50 antifreeze mix? thoughts please !!