Hi, after cooking the head big time on my 300 twice I became paranoid, (both times towing at relative high speeds) and so fitted an aux temp gauge as well as the standard one. I fitted it to the bottom hose because what appears to have been happening was the rad couldnt cope (as it turns out it was partially blocked internally) when things started getting hard work for the engine ie towing at speeds above 50 or lower up steep long hills. So what I was looking at on the temp gauge was the water temp returning back into the engine after its been cooled by the rad, and so an early warning that the engine is about to overheat, (if its returning hot theres only one thing going to happen) that was two years ago and all well so far. although its a bit addictive watching it, you can see the temp rising with trailer/caravan, highest its risen to when working really hard is 85 which seems fine, oh if you put the heater on full then it drops about 5 degrees. You have to remember its not the engine temp your looking at but coolant returning to the engine. Next plan is to replace the normal dash temp gauge as I feel they are far to slow to react (it never moves from normal no mater how hard you drive)