sl;
Welcome to this forum, and congrats on your new acquisition!
High and/or erratic temp indication is a classic symptom of a hard (or intermittent action) failure of VStab (see here:
http://www.sw-em.com/voltage_stabilizer.htm )...ask Graham W.!...so before condemning any part of the temp measuring system, I'd verify VStab output, and also actual temp with another instrument, possibly even an IR "gun style" probe, pointing at various places on Cyl Head or Rad.
See also thread:
https://www.volvoforums.org.uk/showthread.php?t=284381
Good Hunting from Connecticut!