My model 2.5 l petrol 97`Bj. Unfortunately, it remains cold in the interior (Landstr., Autobahn) or lukewarm in the city.The water temperature goes quickly to 90-92. In the city at Stop and Go also times up to 97-99, then however, the fan and the temp. goes down again to 92.5 (acc. to water temp. indicator). At A.T.U. you typed on the heating valve, but a change did not work. I then described as in other articles, the addition pump checked and it did not run. So I took the impeller out of the additional pump and see, the two supply lines got really warm.My indoor room, however, remains lukewarm- cold. What else can it be? Thank you in advance Peter