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The washer theory has been around for over 60 years but is not a cure for over heating. The early radiators had an open over flow off the top of the tank. Later the over flow came out of the neck of the radiator between the top seal of the cap and the seat about 1" down in the neck. A pressure cap was used and the spring loaded bottom end of the pressure cap sat and sealed down on that bottom seat. The spring pressure in the cap varies and determines the amount of pressure the cap will hold. A 4 lb cap is all that is required on the old Fords. A compression leak in the engine will increase the pressure in the system and allow the pressure cap to open and release water. Water temperature much over 200 degrees will also raise the pressure in the system and open the cap. On the early open over flow the water backed out the over flow due to the restriction of the radiator tubes. Well over a gallon of water will back out causeing the engine to over heat on hot days. The restrictors slow the water going into the top tank giving it a little more time to FREE flow through the tubes. With the restrictors not quite a gallon escaped and with slightly more water didn't boil over as much except on days over 80 or 85 degrees then it runs up near or over 200 degrees. With a pressure cap on radiators with a seat down in the neck and the over flow comming out the filler neck or on the early radiators a 3 pound pressure relief valve can be installed in the over flow tube. This with a tight sealing cap will act like a pressure cap. The 144 radiator tube openings in the radiator add up to 3 1/2 square inches, the hoses dumping water in the top tank add up to 4 1/2 square inches so you are trying to put 4 1/2 pounds into a 3 1/2 pound bag. This causes the water to back out the over flow. The washers slowed the water and not as much was lost and the engine ran a little cooler until it got hot outside and they boiled over or run up at 200 degrees or more. With the cap or valve water is forced through the radiator tubes and much more heat is transfered by the tubes and fins. With a pressure cap or 3 lb valve the water can be filled up into the neck and stay there for months as long as the water temperature don't get much over 200 degrees and there is no compression leak putting compression pressure in the system and opening the valve or cap allowing water to excape. The water will stay filled for months with a sealed system with the above conditions. This allows the engine to run much cooler. High volume water pumps moving more water will provide even better cooling. The fans on all of the old Fords don't provide enough air on hot days at very low speed or idle for prolonged operations. There is no problem on 95 or 100 degree days as long as the car is going down the road with a sealed system full of water. Speeds of 75 MPH do not cause high temperature with a good system as described above. G.M.