Quote:
Originally Posted by david.skinner
Many thanks. The radiator cap does not appear to be a pressure cap - i.e no spring and internal seal.
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If the over flow tube comes out from the radiator filler neck you can use a pressure cap as long as there is a washer like seat down at the bottom. If the over flow tube comes off the top of the radiator you need Skips 4 lb valve. To install you slip a short rubber hose on the bottom end of the over flow tube. With the pressure cap or valve fill the coolant up into the filler neck more coolant and more flow equals better cooling. The coolant needs to be forced through the 144 radiator tubes. Due to the number and length of the tubes they become a restriction which causes the water to back out the over flow. With the valve you need to replace the rubber seal in the cap or the cap will leak. One picture shows the 4 lb valve installation and the other shows my 39 which had the over flow from the top of the tank. The filler neck had the bottom washer like seat and I soldered an over flow tube in the neck. and soldered the tube at the top of the tank shut. Be careful the new tube don't hit the pressure cap. Most old Ford pressure caps don't hit good down on the bottom. As shown in the second picture I added the rubber washer. If it don't seat and seal at the bottom it's only a regular radiator cap, not a pressure cap. Don't get the rubber to thick or it will raise the release pressure making it an 8 lb or higher cap. G.M.
I would like to add, take notice of how clean and shiny the radiator tubes are in the 39. This wasn't like this 30 years ago. I didn't have the radiator cleaned but 15 years ago installed Skips high flow turbine impeller pumps and a large bottle of Barr's heavy duty stop leak. This was the type with aluminum flakes in it. The combination of double the water flowing through the radiator tubes and the flakes polished the tubes as far down in them as I can see. I showed my radiator guy and he said he never saw anything like it.