Oil Temp Gauge. . .doesn't work. . .

I just picked up a 94 GSR sedan, and it drives great. . .64k, stored winters, immaculate condition/ super clean. . .only one problem, the oil temp gauge doesn't work. It stays at right at cold (even after a three hour drive). . .a few times it's decided to jump half way up to normal, but that's it. Anyone know what the cause could be? There's a pyrometer and fuel/air gauge cluster hooked up. . .msd ignition. . .electrical/sensor problems? Thanks for any help you can give me!