Engine Cooling problem
1997 Mazda 323 4 cyl Two Wheel Drive Manual 117000 miles

Have had mazda 323f 1997 1.5 for 6 years no major problems, but just over past few weeks if car is taken on motorway temprature hits the hot then comes back down to normal for a short time then back to hot this continues for the whole journey, this was not how it normally performs but as soon as back to round town driving temprature ok exept fan seems to stay on to keep it there, checked all possible probs, coolant level ok turned on heater which works fine very hot really which means water pump working, one thing that puzzles me is that the top pipe from engine is scalding hot but when feeling the air flow from radiator fan it's blowing only luke warm to cold on feeling the bottom hose it's completley cold what's going on i'm not sure if it is a faulty thermostat or blocked radiator or something else.