What is the purpose of the bypass hose around the thermostat on a 65 289? When I drive on cold mornings I have to put a piece of cardboard in front of the radiator to keep it warm. When I don't and I let it warm up enough for the thermostat to open, it will still cool down once I am on the freeway. I have had 4 different thermostats in it so I Know that isn't the problem. That is why I am thinking it has something to do with the bypass around the radiator.