[wombat43402]

I have an 02 v70 185,000 miles that my local volvo mechanics cant figure out. I changed the thermostat last year and ever since then it seems that if the temp is below 20 deg F, the car instantly gives me the red triangle and tells me to stop car safely and the engine is overheating. The temp gauge and warning light both react. At first I was very concerned and stopped the car and let it cool. I went back to my shop and asked if the thermostat could be bad and they did not think so. Of course, when I left it with them for two days it never did it. A few days later it did it again and I was already in the shop vicinity so I wheeled it in and they saw it and just as fast as it pegs the gauge to hot it will instantly go back to normal. I have since bought an OBDII scanner and verified myself that temp runs around 180. Now driving all last summer it did not act up once but as soon as it got cold, sure enough. I have let this car sit outside all night and the instant you turn it over and it is much below freezing it instantly pegs the gauge in the red and gives you a warning. The OBD scanner will not even register till like 120. Sometimes the car reads hot for 30 minutes or it lasts 2 min. The weird thing is if you turn it off when it reads hot it has a hard time restarting..it acts like it is hot????? Yet I have never seen the temp over 190. I took it back to my shop and they have since replaced the ECT sensor and they said it may be trying to cut power to engine thinking it is overheating. Still I have the same problem. I dont leak any coolant and replaced the radiator just a few months ago as well. Any ideas would be greatly appreciated.