[MetroMPG]

wildfire8: the temps were probably "jumping" up and down because your cooling fan was cycling to keep the engine from overheating.

You want to avoid that heat stress and the added electrical load from the fan.

So you need to size your block so the fan doesn't come on in normal use, or simply size it so the temp never goes over your normal operating temp. The ScanGauge is useful that way, since it records max temp experienced during the current trip.