Bottom hose cold engine running hot v6

[racing green rover]

Hi just started using my car after flushing the cooling system along with a new genuine rover thermostat. Everything started off ok for the first hour running between 89-93 degrees on obd display then in traffic temp rose to 100-101 fan come on and cooled it back down to 95 degrees in about 1 minute it then dropped to 92 degrees. Then driving around town i noticed it started running between 96-99 degrees and when stuck in traffic fan came on at 100 initially rose to 102 then eventually dropped down to 96 after about 3-4 minute but wouldn't drop down to 95 to turn the fan off. When i got home i checked the top hose which was red hot however the bottom hose with the bleed screw in was cool i switched the engine off and for some reason the bottom hose got hot again. Iv noticed a slight coolant leak from where one of the rubber hoses goes on the metal rail pipe which goes to the oil cooler. I had to top up the coolant this morning by about a cup full there wasn't no pressure when i unscrewed the cap i changed the coolant last week.I think thermostat might be faulty even though its new.
Anyone any ideas thanks