Help needed a4 bre engine

[Hursty555]

Hi new to the page and hoping for a little help and thanks in advance.

I've recently purchased a 2006 audi a4 2.0 tdi 140 it was a non runner and needed a new coolant flange. Replaced the Flange and got the car back up and running with new anti freeze and air lock removed. Now 3 weeks later I've taken it for mot test and 10 mins later car started to smoke and expansion tank is on minimum we toped it back up and smoke disappeared car passed mot. When I got home just over a mile I noticed expansion tank was again on minimum and again white smoke so I repeated the process but with this time the bottle pressurerised and it settled on maximum no need for water no im suffering with other symptoms

1 no hot air in cabin

2 pipes to heater matrix are some times hot or some times cold

3 water keeps going down to min and back upto max

4 car won't rev over 3500 rpm when driving and car temperature starts to rise but never over heats

The car has no oil in water and no water in oil is the symptoms signs of head gasket or egr cooler failure thanks for taking time to read also now removed thermostat and put it in boiling water and it's stuck shut could that possibly be the problem and be causing all this drama and back pressure 

[Stevey Y]

Hi, sounds like a faulty thermostat or temp sensor or still has air in system or cylinder head temp sensor giving monkey. readings.

Steve.