MRL 360 Coolant Temp 210+

I would FIRST confirm the aftermarket gauge's temp by pointing a laser temp-gauge at the waterpump, t-stathousing and hoses.
I have a SunPro temp gauge in another car that decided to add 20°F to the original temp one day. But the engine is also still running hot because of a partly clogged radiator, so all this didn't help matters when you're driving around and you notice the gauge at 230-240 on the highway.