My Polaris RZR seems to run pretty hot in the dunes. I
have not seen the high temperature warning light yet, but the fan seems to run a
lot. I like to know how things are looking before there is a problem, so it was
time to add a coolant temperature gauge.
Gauge: Summit Racing -
SUM-G2984:

I am typically not a big fan of digital gauges,
but I had already decided on digital for my
voltmeter, so I figured it would
look best to be consistent.
Sending Unit: Summit Racing -
CYB-SENSS6E:

Polaris RZR thermostat housing with sending unit hole drilled and tapped:
Quadovator.com

Quadovator.com also sells a
whole water temperature gauge kit for the Polaris RZR that includes
gauge, sending unit and thermostat housing. If I didn't already
have the gauge and sending unit from Summit Racing, I would have just
bought everything from them.
To install a water temperature gauge in your UTV, you will need to get
the sending unit probe to touch coolant somewhere in the cooling system.
There are two ways to to this. The first is to cut one of the rubber
cooling lines and splice in a coupler that has a port for the sending unit.
The second is to drill and tap a hole into the thermostat housing. I
chose the thermostat housing route because I think it is the cleanest
solution.
I am not that fond of drilling into factory parts so I searched for
another option. That is where I found
Quadovator.com. They sell a
thermostat housing that has already been drilled and tapped for a 1/8 in. x
27 NPT sending unit. Seemed like a great solution so I went that route.

The thermostat is behind the passenger seat just above the oil dipstick.
Remove the factory thermostat (2 - 10mm bolts).

New thermostat with temperature sender on the left and the factory
thermostat on the right.

Install the new thermostat housing. No gasket is used, but make sure
the mounting surface is clean of debris. Once the thermostat housing has been swapped, install the sending unit.
Now it is time to connect the wiring up for the gauge. Black wire goes
to chassis ground. Red goes to 12V (ignition hot), purple is 12V when
your lights are on (dimmer) and blue comes from the sending unit.
On the RZR, there is a orange wire with a butt connector that is used for
a winch. This wire is hot only when the key is on (ignition hot). I
connected the red wire from the gauge to this orange wire.
For the purple dimmer wire, I spliced into the green wire that goes to
the factory headlight switch. This wire is hot only when the lights are on.
Then run a wire from the gauge on the dash back to the sending unit.

Top off the radiator with distilled water. I added one-half a bottle
of Redline Water Wetter while I was at it.