Volvo 850 stalls when engine gets warm

[Annema1]

I finally managed to get the housing of and replace the thermostat since I only just now got the proper tools. Unfortunately the thermostat was, although being 21 years old, still in near mint condition. I did replace it and check the old one, but it did open and close properly when heated to 90 C. I don't know if it is supposed to start opening at around 75 C, wich it does with mine, but it is only a very narrow state.

I now have no clue what so ever at what could be my problem. Is there anything else I can check or test? I am running out of hope.

Thanks in advance,
Sergej

[bmdubya1198]

These thermostats are supposed to start to open somewhere around 89-92 C.