88 volvo 240 wagon. I've had to replace the fan clutch, rad, hoses, tstat (180 degree) and water pump most recently. When I idle, the temp is right at the dot in the middle. On the highway, it rises to about 3/4. Sometimes it returns to normal. It lowers to the dot when i turn the heater on. I'm kind of stumped. I also bypassed the temp. compensation board. otherwise the car runs beautifully. Its had a tune up and a new head/valves (previous owner thankfully).