Thermostat choice

[RL 325i]

some of you might know I failed Smog because of extreme high NO measure.

I am already looking into getting a new cat, O2 sensor, plug, coolant, TB etc... pretty much a major tune up.

I notice that the temperature of the car after driving 30 minutes. it only reach 1/4 of the mark.

Someone I talked to suggested one of the high NO reading is because the engine runing too cold. He said my normal temp reading should be half mark. He suggested that I should replace a hotter Thermostat.
I am about to order it on line. they listed 3 temperatures. 71,75, and 80 degree. Which should I get to get my car run hotter.
Help pls.
Ron

[blueapplesoda]

71 will run the coldest, 80 the hottest, of the three. i am running 80,which overheats my car (no aux fan), and thats in Socal valley summer weather, which is like avg 100 at noon, and arid. With aux fan i can stay around 1/2 w/o ac and 3/4 with ac.

[powellsd]

one i am glad i dont have to screw with smog test and two i would do the 75 or 80.

[fretburnr]

sounds like your thermostat isn't closing or opening properly, your current temp range may not be a bad choice but maybe just replacing it will clear up the problem