V70 R; runs hot, runs cool depending on speed

I have a 2000 V70 R wagon, with only about 75,000 miles on it, and this is my first winter with it; thus it may have been doing this all along, and I have not noticed until now. From a cold start, if I drive in the city, with a lot of starts, stops, and idling, it seems the car heater does just fine. It gets warm, and the temperature gauge travels to the midpoint on the scale (though it does not get hot as fast as my 740). Also from a cold start, if I drive it on the Freeway (60-75 mph), it seems that the car heater never gets really warm, AND the temperature gauge usually does not get past the first "white line" on the bottom of the scale. I've had this car on the freeway for hours at a time, and this is the behavior I get. And to add to the mystery, if I drive it in the city and it gets warm, and then I get on the freeway and drive for while, the heater seems to cool off, AND the temperature gauge drops back down (as if the engine is running cool). This car (and the heat) seems to run cooler when it's at higher speeds, but this makes no sense to me. Other than being possessed, what on Earth can explain why this car is doing this? The addition to the mystery (for me) is that the heater AND the in-dash temperatue gauge are both conspiring in this. Help! (What do I have to fix?)

mines been doing the same & think its down to needing a new thermostat, i'll get round to changing it one day :emoticon_U:

My V70R does the same in the lower winter temps, I had a new thermostat fitted last sept......

i would change it again :D IIRC there are two different temp thermostats, so i would check you have the correct one... either way, if the thermostat is operating correctly it shouldnt be running cold whatever the conditions

Yes, new thermostat required. Here's how:

and another thing.... 

And when you do replace the thermostat, don't drop the bolt down the back of the alternator..... Does anyone sell 7mm bolts on a Sunday - not round me they don't - oh and the RAC don't even carry them in their vans. Joy of joys!

Yup fix the thermostat. I think the car runs rich until it gets warm to help speed the warming, so you'll be guzzling more fuel than needs be.