We have a 1957 Buick Roadmaster Conv that has been heating for years. We have tried everything we could think of including: - rebuilt water pump - larger diameter and more agressive fan - fan shroud - new 4 core aluminum rad - various diameter water pump pulleys - flushing the rad and block (repeatedly) - thermostat (currently running without) - checking block and heads for cracks Since we have done all of this, it now seems to only run hot on the highway. We will add the thermostat back into it, but I really would like to know what the original water pump diameter was. I want to ensure this is not a contributing factor. The car does not have AC, if that changes anything. Any suggestions or comments would be sincerely appreciated! Thanks!