Hello. I've been searching the boards for a while now and can't seem to find a completely similar situation.

I have a 1999 V70, base model no turbo. I noticed while driving to WV(~33degrees) last week to go snowboarding my car was running very cold while driving on the interstate, but when I pulled over to get some food and check it out it warmed right up to where it's supposed to be. The same thing happened last night while driving to Charleston (40 degrees)

Also, the coolant needs to be topped up every month or so. I don't think I need a new heater core, coolant isn't leaking on the floorboards

 

Most likely time for a new thermostat. Read up on it hear if you don't know how to do this. Consider doing an antifreeze change while your at it if it's near due.

Jerry

 

May need thermostat replacement

as well pressure test system

maybe a leaking heater core?