| 4ford | -- 10-27-2010 @ 6:09 PM |
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Just put in a radiator.. an aluminum one not split but has two inlets and two outlets. The radiator cap hole is smaller then the old one that was in the car. So what presure should the cap be? I put on a 13lb one but will that be ok? Thanks Mike
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| trjford8 | -- 10-27-2010 @ 8:39 PM |
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Mike 13 lbs is fine for the radiator, but the water pumps and motor(heads,gaskets,etc) may not tolerate that much pressure. I would be inclined to run a 7 lb. cap.I've run the 7 lb.cap with no problems.
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| Old Henry | -- 10-27-2010 @ 9:36 PM |
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The stock cap is only 4 lbs. You might want to consider that as the limit of pressure the stock system was designed to hold. That's all I've ever had and it's worked fine. Still Old Henry
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| 42wagon | -- 10-28-2010 @ 3:21 AM |
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This will probably start a firestorm of protest however the 41-48 Ford book says that for 41 and 42 the radiator cap was not a pressure cap. Sometime during the war and certainly in time for the 46 model year a 3.5 to 4.5 lb pressure cap was released. However on 4-22-47 it was announced that the pressure cap would no longer be used for passenger car production. Don't know what all this means except my 42 runs just fine with an unpressurized cooling system. Ted
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| supereal | -- 10-28-2010 @ 9:37 AM |
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The caps are generally available in four "flavors": no pressure, 4#, 7#, 10#. 13 pounds is too much, in any case, but if your filler neck is non-standard, it may only take that type. A pressure cap is important for several reasons, including retention of the coolant during temperature expansion, and reducing "hot spots" in the water jacket that produce steam, compromising cooling. The 41-48 book does say that the 41A caps were discontinued in production, but seems unclear as to what was then installed on the line. The "green book" shows variations of the pressure cap continue to be offered under different suffixes at least thru '48. The 41-48 book is silent regarding the replacement part. It would seem reasonable to conclude that the discontinued production cap was succeeded by a similar pressure version.
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| 4ford | -- 10-28-2010 @ 11:03 AM |
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the neck is the standerd size but differnt than stock (smaller) so it looks like i should get one that is lower pressure. This systom is an open non pressure? Thanks guys Mike
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| supereal | -- 10-28-2010 @ 1:30 PM |
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All systems benefit from some pressure. That is why Skip Haney's overflow valve works on non-pressured systems to prevent loss of coolant by raising the internal pressure. The '41 usually didn't have a pressure cap, but many were later installed. There was a transition in '41 from the split core style radiator to the single core that went on to the '42 year. Those were chaotic years as the war began, making changes rapids and often poorly documented. Very early radiators were not designed for pressure, and the tanks may not survive pressure above 4 pounds. The new turbine style water pumps provide some extra pressure to reduce the "tea kettleing" hot spots, as well.
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| Old Henry | -- 10-28-2010 @ 2:02 PM |
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This may be overkill, but, if anyone is interested in the science, here it is. At sea level the average atmospheric pressure is about 15 psi (14.69 to be exact but I'm going to use round numbers for illustration.) At that pressure, water boils at 212 degrees farenheit. As pressure rises, so does the boiling point. The stock, 4 lb. radiator cap raises the pressure to 19 psi such that water won't boil until it reaches 225 degrees. In other words, the water (and engine) can get 13 degrees hotter with that cap on before the pressure of the water overcomes the pressure of the cap and the water boils and keeps the water and engine from getting any hotter than that. The 13 lb cap discussed raises the pressure to 28 psi (almost double the atmospheric pressure at sea level) and the boiling temperature to 246 degrees at sea level. So, the question is, how much pressure can the system hold and how hot do you want the engine to get before the water boils to limit it going any higher? For me, I like to stick with the stock cap to maintain the originally engineered pressure and "pop-off" temperature. Here's one possible use of alternate pressure caps for different elevations: The average atmospheric pressure of 15 psi at sea level reduces to 12 psi at 5,000 feet elevation where I live. So, if you live at a high altitude and want to maintain the same boiling temperature as sea level you can add radiator cap pressure to maintain that. So, my stock 4 lb. radiator cap at my elevation of 5,000 feet is about the same as no pressure cap at sea level. Or, in other words, if you wanted to maintain the stock 19 psi internal system pressure and corresponding "pop-off" temperature (with the stock 4 lb. cap) when you made your Pike's Peak climb to 14,000 feet in the middle of the summer, you'd need to add 5-6 lbs. of pressure to your cap. So, then the 10 lb. cap might make sense. Get it? The 10 lb. cap at 14,000 feet is the same as the 4 lb. cap at sea level. And, (add nauseum) without any pressure cap at the top of Pike's Peak, your water will boil at 183 degrees! before some thermostats even open! Don't know if anyone wanted to know THIS much about this subject but now you do. Still Old Henry This message was edited by Old Henry on 10-28-10 @ 9:53 PM
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| Stroker | -- 10-28-2010 @ 2:59 PM |
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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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| ford38v8 | -- 10-28-2010 @ 6:23 PM |
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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
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| 4ford | -- 10-28-2010 @ 7:10 PM |
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thanks again for all your help!!!! mike
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| Old Henry | -- 10-28-2010 @ 8:01 PM |
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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
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| tbirdhandyman | -- 11-03-2010 @ 6:08 PM |
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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
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| Old Henry | -- 11-03-2010 @ 10:03 PM |
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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
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| TomO | -- 11-04-2010 @ 8:42 AM |
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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
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| ford38v8 | -- 11-04-2010 @ 1:15 PM |
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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
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| TomO | -- 11-05-2010 @ 5:01 PM |
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Alan you are correct, I had a mind check. Tom
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| supereal | -- 11-06-2010 @ 10:26 AM |
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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.
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