I guess it's interesting that this subject has come up again at the end of the summer, just like last year. I just recently went through this process again, myself. I have chronicled my trials of upgrading my radiator to resolve the persistent overheating problem elsewhere on this forum, and to summarize the results, I found that changing from a brass to an upgraded aluminum radiator (1.5 inch double row vs the original brass 1.25 double row) and using straight distilled water with two bottles of Water Wetter resolved the overheating problem. Note here that I was not using any thermostat; just a restrictor plate (this was on the advice of the builder). However, I found that in the cooler weather, the engine would not heat up properly, and this was reflected with a decrease in performance and an increase in
oil consumption. As an example, I went to another member's summer home up in the cooler area of the state about a month ago. On the way home, with the outside air temps around 60 or 65 degrees, I found that, on the road at 75 mph, the engine would not heat up over 140 degrees until I got back down into the warmer (90 degree) weather of the valley. Based on the results of the various studies I have seen on the effects of running the engine too cool, I opted to install a 180 degree thermostat and now the engine runs at the proper temperature with better performance. These are my results; YMMV.