My daily micra encountered a problem

I was reversed into with a towbar. Towbar damaged my radiator but it didn't leak. I plan on going on a long distance journey so I thought I'd replace with a scrappy radiator. That second hand radiator would heat up above operating temperatures. I ended up buying a new radiator but then the new radiator would never heat up from cold or get to operating temperature. My mpg has also gone down the drain.

If you start the car from cold and drive it 70mph for 12 miles the temperature needle will move up 2mm. The minute you stop it slowly climbs to 3/4th of the way. You start driving and it cools down again. I've never seen the fan turn on since this problem.

New radiator
New themrostat not genuine
New temp sensor not genuine
Fresh coolant (pink)
New air filter
New fuel pump and oil filter with fresh oil change

Still get bad fuel milage along with the temperature problem

£20 for 115 miles
Possibly a bad thermostat , even new can be faulty , isnt a auto radiator?, They are abit thicker then even the 1.3 version,
Sounds like when mine started to go took forever or sat , or flogged it to get up to temp, but heater or cruise would cooled down real quick ,
Case of take the thermostat out and put it in boiling water should slowly open the take out and close

Sent from my moto g(6) using Micra Sports Club mobile app
Maybe a incorrectly seated new thermostat? Your description is clear, your thermostat is stuck wide open. My Micra has this too, hoping to solve that tomorrow with a new thermostat. You can test by starting a cold engine and feel the lower hose at the radiator. If it stays cold for a while that is good and if it warms quite soon your thermostat is not functioning properly.