I was having a problem with the temp running higher than it should. Ihad replaced the engine with the new metric motor one. replaced the radiator, hoses etc... burped it also.
I was getting nervous seeing the gauge getting up there around 100. bought a Infra red temp lazer gun, shot different areas of the engine, and didn`t seem to bee too hot.
even changed the gauge, and bought new temp senders.
I read some where here on the forum of using a Thermostat for a SLC. think they are 75C. put it in and seemed to help some.
I did have a problem with the gauge later on, suddenly shoot up and peg at the top.

that will get your attention. Jump out of the car with the Lazer temp thing in hand, and start shooting the engine. discovered shutting off the engine, and restarting, the gauge would drop back to a normal range. sometimes turning on/off a switch would make it jump.
Discovered the ground strap from the engine to body wasn`t making a good connection. removed it, cleaned up the contact areas, and all has been well.
So check your grounds well.
Charlie