7 pound radiator cap

Mopar General Discussions

  1. barbee6043

    barbee6043 barbee 6043 FABO Gold Member

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    I was told bt shop that has been in business to use 7 # cap, that was oem and it would good as my rad are 50 years old?! anyone using 7 # cap???????
     
  2. bbrroowwnn

    bbrroowwnn never re member

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    I always use 15 or 16 lb cap.....What they mean is it would be better with less pressure in case there is a weak spot after 50 years, but honestly if it gets a hole it needed to be redone anyway.....You get 3 degrees of temperature per pound of pressure....In other words, water boils at 212 degrees so with a 7 lb. cap you are gaining 21 extra degrees before you boil over.....which would be 233 degrees before it spewed.....16 lb. cap will get you 48 degrees which is about 260 degrees.....just so you know
     
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    • TrailBeast

      TrailBeast AKA Mopars4us on Youtube

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    • barbee6043

      barbee6043 barbee 6043 FABO Gold Member

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      thanks for the info. I have always used the 14 or 16 lb caps. the upper tanks had been incorrectly repaired before me, and the other had a couple of minut pin holes in tank. I figured the less pressure in it the less likely to develop another leak...
      I really appreciate this guy. he repaired both my rads for total of $30. some guys want $45 just to pressure test them. we all know it is hard to find a repairable original rad. not all of us that have several old projects can afford a $450 repop correct rad or want the alum wonder.
       
    • perfacar

      perfacar Well-Known Member

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      the bigger the tanks, less pressure is needed.17 # are for small tanks. this from a radiator shop. there's a reason why older cars had lower pressures!!I seen a 16# cap on early car, split the seam.
       
    • AJ/FormS

      AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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      I have been using 7 pounders for 30 years or so.
      If your ancient,cooling system does what it was designed to do,it will do it at atmospheric. At 7psi, your rad,your heater core, and your hoses, will last for decades.
      Hi-pressure caps were designed for modern,marginally sized, hot-running,going for minimum emissions, cooling systems.Our classic weren't.
      Our classics have generous sized rads, and rad openings,have available efficient waterpumps and direct-drive fans, and most guys run 185*stats, or less.We run fat carbs, not lean EFIs. We run big oilpans with 6,or 7 or 8 qts of oil in them. we run auxiliary tranny coolers, and headers with generous sized pipes,and low restriction mufflers. All these things add up to;Our cooling systems having a pretty easy time.
      I've run cams up to the 292/509. Once the tune was in it, I couldnt overheat it.I run the stat at 205*and straight water, with the additive pkg to lube the pump-seal.
      Of course, here in Manitoba, our summers are relatively cool, with daytime temps rarely over 32*C/90*F, and only for a a week or so in July.
      Your results may vary.
       
    • 67Dart273

      67Dart273 FABO Gold Member FABO Gold Member

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      If your car doesn't run hot and you don't need a "big" cap go ahead and run with less pressure. It's easier on hoses and radiators.
       
    • limegreen70

      limegreen70 Pokorny Enterprise's

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      My dad had a 2 core radiator with a 7 pound cap ran it for 15 years that way then the cap went he couldn't find a 7 pound cap so he used a 16 he was weary about it since it was a old radiator but nothing ever happened worked fine.
       
    • barbee6043

      barbee6043 barbee 6043 FABO Gold Member

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      thanks for the feedback. as I have said before, I have forgot half what I knew, and the other I never knew!!
       
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