Freelander overheating!

Hello, what a great forum! Hope you can help me with mye '03 1.8 petrol freebie..

- when starting engines, temp guage show cold and reach mid temp as normal.
- Driving normal show no sign of overheating of engine, but when driving upwords or with trailer in 4th and 3 - 3,5K rpm, temp guage suddenly start to rise.. If i dont put it in 3rd and lower the rpm, it overheat and coolant comes out of header tank..
- If i stop and idle, it will take about 30sec until the guage is back to mid temp again..

- The car has stand still for about 6 weeks cause of repairs, and one of the things i've done was to change the coolant and replace the thermostat.
I did another flush, change back to the old thermostat and added new coolant the first time the temp guage suddenly was on the red..!

- I've tried to get the air out the way it was described in Haynes, but I suspect its more trapped inside..
What to do...?

The thermostat is the new type[emoji6]

Did you bleed with heater full on?
Did you use both bleed screws?
Is the water flowing into the water bottle from the small pipe? If not try blowing down it. I think I read somewhere there is a valve can stick shut.

Tanks for help!
I have checked that the valve is not stuck, the heater was on full when i bled, and I open up both bleed screws.
Have tried to bleed 4 or 5 times on the hose that gods into the heater, the second time it got better, but it's still overheating.

Is the radiator in good condition? I've seen photos of them with hardly any fins. Have you tried squeezing the top hose with the engine running and the lid off the header tank.
When was the water pump last replaced? If the car was run without antifreeze in the past they can be rusted up pretty bad.

The radiator is in good condition. The water pump was actually replaced only two years ago, together with the timing belt. But its a good idea to check the water pump again
When I squeeze the upper hose from the rad, water comes into the header tank, don't know if it is air together with it.
Is it a tought to replace the water temp sensor?

If the water is flowing into the header tank then it isn't the pump but could be a thermostat.
When I bled mine recently it was a very easy quick job. Is it possible some idiot has put Kseal or similar in it, if so it could have blocked the system up.

Maybe some debries has losened when I flushed the rad and engine and blocked some place.. Cause it has worked fine the last two years.
I will trie to flush and replace coolant one more time i think