There was a post several weeks ago with some calculations for operating a 6 volt fuel gauge on 12 volts (OlBlue). His math showed 2.71 watts on 12 volts. To my limited knowledge, using a higher rated resistor or diode (watts) won't cause any problem...it's like using a heavier extension cord when your trimming the hedge.
Edit. Doesn't the voltage rating of your diode have to be at least that of your intended input voltage?
Edit/Edit. I just found a little Zener selector chart and put in values that would represent a voltage drop from 14.0 volts to approximately 6.0 volts. The diode you spec'd popped up! This tells me one important thing...I don't know a darn thing about this kind of stuff.