Either way, too cold or too hot, is not good. Too much wear, too poor running, too poor of fuel economy, etc. My experience has been too cold, but mainly in the Wisconsin winters......Roy is right though, and so is science.....not enough time for the heat exchange to take place can result in overheating, with a radiator that was designed for lower flow rates. High flow rates can result in too cool of an engine if the radiator is oversized. The engine should be warm enough to get any condensation to evaporate out of the oil, too.
