Have a 93 lightning. Oil temp gauges do not read anything. What should I look for?

Here is a quick guess, when my 47' sits for a while and when i go to start the motors at least 1 of the 3 oil temp gauges don't work and sometimes I have to flick the gauge then the needle fires up to the temp its reading. I also had a certain time where the thermostat is stuck and I have had those pop open after running for a few min. I'm sick of the thremostats getting stuck sometimes they never open so I'm in the process of pulling them all out and letting the engines free flow.

1997 47' Fountain Lightning