Volvo Repair: 86 740 GLE running hotter than normal, improper installation, timing belt

Question
My '86 740 GLE four-cyl has been running hotter than normal for the past couple of days.  Had the timing belt changed on Monday. On Wednesday the abnormal temp behavior began. It is now Friday.  Could the improper installation of the timing belt cause this problem?  Car behaves as if the thermostat is the problem (needle moves toward the "hot" side of the dial, then shifts back to a "normal" position slightly to the left of the center mark).  

Answer
Ben, if it was installed improperly, car would run poorly.  If would have to be off quite a bit for it to get that hot.  I would check the fan. It may also be a temperamental gauge sender.  Check to see if car is actually running hot.  A thermal thermometer would help.    Roger