Cooling system not up to temp

The gauge reading isn't important. What's important is whether it's reaching the proper temperature. You can measure it with a thermometer, but a more accurate way is to read it on the live sensor data with a scanner. It should reach near 200 degrees. The gauge and the Engine Computer use different temperature sensors, and the computer's sensor is the important one.

The dash gauge on my '88 Grand Caravan barely reaches quarter scale but the heater will roast you out. If your heater is working properly, you might try a new sending unit, (single wire) for the gauge even though they rarely fail.

Caradiodoc