My temp needle has always hung a bit to the right of the centerline on the dash gauge. Even though I have a high capacity aluminum radiator, my car always runs a bit warm, about 200 degrees F when measuring coolant temp in the radiator. I finally decided to do something about it. So I bought a new 180 degree thermostat from MSA. To verify things were operating correctly, I removed the existing 190 degree thermostat, cleaned it, and put both thermostats in a pan on the stove. I suspended the thermostats on a piece of wire so they didn't touch the bottom of the pan. The 180 didn't open until 189 degrees, and the two year old 190 didn't open until 198 degrees. Since both appeared off in the same direction, I decided it would be prudent to verify calibration of my electronic thermomerter. I checked it in both boiling water and ice. As a back-up, I compared it's readings to a regular thermometer. Both read exactly the same and were dead accurate. Both my thermostats appeared to be opening late... So off I went Napa Auto. They didn't have a 175 degree thermostat, so I got a 160 degree. Sure enough, it didn't start opening until almost 170 degrees. I figured that is still better and installed it in the car. A temp check of coolant now reads 173 degrees, and the dash temp gauge needle rests a little to the left of center. I think a 175 degree would have been perfect, but I'll stay with the 160. I'd rather the engine run a few degrees cooler than warmer. BTW, just for grins I just looked at some oil viscosity curves, and the small difference in operating temp makes no significant difference. I "might" be able to detect a small drop in fuel efficiency, but time will tell. The real moral of this story is, check the operation of a new thermostat BEFORE installing it...