Volvo 14 engine temp. Low

Hi there
I get ride of an 14 Volvo used some 34 clicks
When riding it get a long time to get the engine heated to 170 degrees. I kept it running 10-15 mins before the ride some 30-40 mins ride I take ... After the ride I parked it but did not shut down the engine . I check that as I stopped it the temp level falls dramatically to zero in 4-5 mins
And the fan was running too .
It was -10 outside ... Is it malfunctioning or normal behaviour of the truck .