I noticed that my CX550 C 1980 was running hot and discovered that the fan had become unscrewed. After reattaching it and with new Stant radiator cap, 50/50 water coolant solution, new sensor and new thermostat, on the freeway on a day in 70s (F), the needle goes to the middle of the thick line, which is not much better than before. Perhaps my memory fails me, but it seemed like before the temperature was quite stable, rarely moving from where the thin and thick lines meet. My guess is that the coolant is not circulating fast enough, and the only problem I can think of is that I replaced the stock rubber hoses with some with a slightly smaller inner diameter, but it doesn’t seem like this should make much difference in performance. Does anyone have any ideas of what might be the problem?