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EFV-8 Club Forum / General Ford Discussion / radiator cap presure 1941 flat head

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Posted By Discussion Topic: radiator cap presure 1941 flat head -- page: 1 2     supereal 11-06-2010 @ 10:26 AM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 I dug out my collections of service bulletins, and found two regarding radiator caps. The first is dated July 7, 1947, and was superseded in April 28, 1948, with the instruction to destroy the earlier page. It shows 5 radiator caps, all pressure rated for a range of 3.5 to 4.5 pounds. They are 21TA-8100-a, 41A-8100-A1&3, 41A-8100 A2, 41A-8100-B, and 26H-8100-B1. There is no information, beside this list, as to why any no pressure caps were listed. TomO 11-05-2010 @ 5:01 PM reply profile send p.m. Senior Posts: 7256 Joined: Oct 2009 Alan you are correct, I had a mind check. Tom ford38v8 11-04-2010 @ 1:15 PM reply profile send p.m. Senior Posts: 2765 Joined: Oct 2009 Tom, I know you won't disagree with me on this, just a slip of the (keyboard) mind, I guess: Your statement that the Club book would be the final word at a V8 meet doesn't quite make it. If that were true, then all research could cease, and the Judging Standards Committee could retire. The other half of your statement is true, of course: An owner must present documentation of any variance from the accepted norm at the Concourse, preferably to the Chief Judge or his designate before judging begins. If there remains a doubt as to possible correctness, that doubt will be resolved in favor of the owner. Alan TomO 11-04-2010 @ 8:42 AM reply profile send p.m. Senior Posts: 7256 Joined: Oct 2009 The first pressure cap that I can find in the parts catalogs is in 1940, P/N 09B-8100.This cap does not show up in the 1942 catalog and neither does the 41A cap, which shows up in the 1948 Mercury catalog for all Mercury's from 1939-1948. Parts catalogs are not good indicators of when a part was introduced or discontinued. The right outside mirror, for a 1940 Ford, does not show up in the parts catalogs until later 1941 and factory letters show that it was introduced some time in early 1940. Parts discontinued in production were listed in parts catalogs until the supply was diminished enough to discontinue listing the part. Factory letters were sent out to update the dealers with the most current information. The 41A-8100 radiator cap was available from Ford dealers well into the 1960's. When you are having your car judged at a V-8 Club meet, the Club book would be the final word, unless you can prove that your car was delivered with different equipment. Tom Old Henry 11-03-2010 @ 10:03 PM reply profile send p.m. Senior Posts: 738 Joined: Apr 2010 The green book lists cap number 41A-8100-A as a pressure cap for 38-48. I don't know how that jives with the 41-48 book that says the pressure cap was discontinued in April 1947 according to Ford P & A letter #48. (Appendix D-4 of 41-48 book) Still Old Henry tbirdhandyman 11-03-2010 @ 6:08 PM reply profile send p.m. Member Posts: 51 Joined: Oct 2009 On my '41 Mercury, I use a Ford script cap that has the part number "41A-8100-A2" on it along with "3.5 to 4.5 LBS." I use a coolant recovery tank with this cap and my car does not run hot even in the 100+ Houston, TX heat. Someone with a parts book might look this number up and see when Ford went to a pressure system. Robert E. Tbirdhandyman Old Henry 10-28-2010 @ 8:01 PM reply profile send p.m. Senior Posts: 738 Joined: Apr 2010 Alan, I think we are both making the same point. I wasn't suggesting going high altitude without pressure cap to create a LOWER boiling temperature to cool the engine better. As you said, once the water turns to steam and is gone, it is no longer cooling the engine. My suggestion was just the opposite, that at higher altitudes one needs MORE pressure to PREVENT boiling over so that the water will stay in the system cooling the engine and NOT leave as steam. Still Old Henry 4ford 10-28-2010 @ 7:10 PM reply profile send p.m. Member Posts: 88 Joined: Oct 2010 thanks again for all your help!!!! mike ford38v8 10-28-2010 @ 6:23 PM reply profile send p.m. Senior Posts: 2765 Joined: Oct 2009 Old Henry, your science is good, but for one glaring mistake: As it is true that water cannot be heated beyond the boiling point, it is also true that a water cooled engine cannot transfer its heat through steam, no matter what the temperature of that steam is. A high altitude (low pressure) system will boil its coolant at a lower temperature than at sea level, but cannot reduce the engine temperature beyond that lower temperature either. Alan Stroker 10-28-2010 @ 2:59 PM reply profile send p.m. Senior Posts: 1460 Joined: Oct 2009 Well stated Ol Henry! I might add that for those of us who live in freezing climes, anti freeze, (while not as efficient a coolant as pure water), also raises the boiling point. I run a 4 lb. cap on my 38 which is about all I dare run due to the pancake configuration of the header tank. My elevation is only 840 feet, so the 4 lb. cap plus 50% glycol bumps the boiling point somewhat higher. A properly maintained early Ford cooling system is generally adequate except when pulling long mountain grades, or putting along in parades. With our 40 Ford ton-and-a-half, hauling hay in 100+ deg. F. heat from below sea level from the Imperial Valley to it's destination at 2000 feet would require a couple of "rest stops", and some make-up coolant from the always present "water bag". Heavy traffic or parade duty sometimes requires keeping the RPM's up to let the pumps and fan do their job. I think we have become so accustomed to modern high-efficiency, high-pressure electric fan-boosted cooling systems, that we forget how challenging something like climbing a mountain can be whether it's in a vintage Ford, Ch*vy, or Plowmouth.

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