87 Quad running cold

[WindChill]

My 87 Quad temp gage is reading cooler than normal. Gage, in the past, never reads more than 175 even on hot days. A couple of simple questions. Rather be safe than sorry. Thermostat, to remove and test do I have to also drain/refill coolant at the same time or can I just remove the thermostat test it and replace? Coolant temp gage sending unit. Looking at the manual it's hard to see exactly where it is. Is it inside the black intake duct? Took the wire off the high water temp light sending unit grounded it and turned on key. Temp gage needle did not move.
Temp gage does move up a bit when driving half way to 175. Danger to drive?
No coolant leaking. Car runs well while driving.
Of course its Sunday and I'm 2 hours from home and my garage!
Comments appreciated.

Windchill
87 Quad

[ghnl]

I'd suggest draining at least some of the coolant before removing the T-stat. If you don't want to bother with crawling underneath and opening the radiator drain, you can use a small hose and siphon out a gallon or so. For sure follow the refill/bleed procedure when you're done.

The temp sensor is not in the black duct work - it's in the intake area. Kinda buried below the wires & connections for the fuel injectors, etc. BTW, there are a couple of temp sensors. One for the ECU (computers), the other for the gauge.

The picture below shows the sensor for the ECU (CTS = coolant temp sensor), the sensor for the gauge is located a little bit forwards of the one shown and has single spade terminal, IIRC. (picture from the L-jet diagnosis page)