Do not install a clock in your dash. Every time I leave in my Cobra, when I return my wife wants to know why I have been gone so long. I tell her I lost track of time. If you don't have a clock in the dash and you conveniently forget to wear your watch, how will you know what time it is? Just because you are gone 3 hours to get gas and return with less gas than you left with at least you will have an excuse: "I just lost track of time!" (I unplugged my clock and told my wife it is broken.) The
oil temp gauge would be my choice.