This info may help someone out, my 150 cdti had been struggling to reach 70 degrees on the needle and noticed the car had poor performance anything under 2k rpm so decided to have a new thermostat fiitted (gen VX) Anyway the mechanic said its fairly common on a lot of new VX to have this fault and i should notice a difference in performance and mpg. Well after a 15 mile drive i can report a massive change in performance. It seems to pull alot better once up to about 80 degress then flies at 85 degrees. No more sluggishness (if thats a word ha ha). I cant report on the mpg yet but will do in the next few days. Im not familiar with ecu's but maybe the engine is restricted until correct operating temp is reach??? This is my opinion and prob wrong but i thought it would be worth a mention on this site. Cheers guys and girls.