I was driving my Z24 down to Yellowstone NP after I rebuilt that engine. I made it all the way to the park and I looked over at my oil pressure and it was LOW the oil temp gauge was almost maxed out. I was like oh shit, pulled over, when it idled down the oil pressure dropped to like 2 lbs. The car had boiled over internally, causing an air pocket to stay in the system and not let the gauge read the coolant temp, it said 195 degrees. I opened the hood and I was like...yeah right 195 my $$$. Apparently at that altitude you need to actually have coolant in your system cuz water will boil out
Point being, install yourself an oil temp gauge, in the pan, its far more reliable than a water temp gauge. That is why things like Airplanes, Helicopters and Corvettes monitor the oil temp more than the water temp.
Its cheap insurance, and it saved me a motor.