2 style radiator caps- where to buy what I need

Heating / Cooling / AC

  1. Syleng1

    Syleng1 Karma is real and Life is short... FABO Gold Member

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    EB94D700-784E-4B42-A781-30E12D2CA085.jpeg So on my 66’ I installed my original rebuilt 273’ and it runs great. I also removed the aluminum radiator and installed the factory copper installed with a shroud and clutch fan for originally. The radiator was re-cord and pressure tested. It was expensive but well done by a reputable radiator shop.

    So to get to the meat of the issue- my radiator cap dribbles when the car is shut off. I pressure checked the cap and the tank. Both good to needed pressure. Current cap is 13psi and radiator tests good to 18psi.
    No leaks. I called the radiator shop and they told me that those older radiator are designed to leak off pressure when they shut off because the engine goes a tad hotter due to lack of coolant flow and the pressure increases. The cap purges any above the line coolant to find its happy place. Most caps today are designed for a recovery bottle because when the car shut off the radiator cap opens a bit so as the coolant cools it sucks antifreeze back into the system.

    It seems I have a recover style cap on my old style radiator. Where the hell do I find this style cap. I’m looking for a Chrysler cap for my original style engine bay. Tech help at all the companies I called cannot give me that info. I did how ever confirm there are in fact 2 style caps for 2 different applications. The radiator shop was not BSing me. Side Note: I do not want a recovery bottle, the car did not come with it. I just need a source for a factory radiator cap for a 66’ 273 with a/c. (HD cooling)
     
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    • toolmanmike

      toolmanmike Moderator Staff Member FABO Gold Member

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    • pishta

      pishta I know I'm right....

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      My 65 had the same rubber overflow line (smaller gauge) clipped to the side of the rad. I thought for sure there was something on the end but nope, a dribbler. It should not even dribble under normal working conditions. Even when the motor gets heat soak, the pressure rating should not exceed the cap or you would be topping the rad off every 3 months. Most AL aftermarket rads dont use a Mopar cap. That $25 cap looks right.
       
    • Mattax

      Mattax Just the facts, ma'am FABO Gold Member

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      Moparts forum often has info on correct appearances.
      Got this from there. There may be otehr variations on the original caps appearancewise if they came from different suppliers.
      upload_2021-8-16_10-14-43.jpeg

      Try contacting BE&A, or Bob and Glen-Ray Radiators.
       
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      • bcschief

        bcschief Well-Known Member

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        You may also be overfilling the radiator coolant should just cover the core or about 1 inch below the cap seal on a non overflow system. This is to allow for the coolant to expand and not be pushed out the vent tube.
         
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        • Dana67Dart

          Dana67Dart The parts you don't add don't cause you no trouble FABO Gold Member

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          Best move you ever made!

          Is there coolant coming out the drip tube or from under the cap?

          If from the drip tube, the coolant has not found it's level yet

          If from under the rad cap either the cap doesn't seal to the rad fill hole, or is missing a seal.
          There should be a rubber gasket that contacts the top of the radiator fill hole, and a second that contacts the inside of the rad fill hole.
          Should look like this.
          Screenshot_20210816-083428.png

          I have never found a different cap for a recovery system vs a non recovery system, not to say that they don't exist but I don't know what would be different?

          Any of these should work fine. If these leak under the cap I would go to the rad shop and make sure the filler neck is correct for the application

          Screenshot_20210816-084544.png
           
          Last edited: Aug 16, 2021
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          • Syleng1

            Syleng1 Karma is real and Life is short... FABO Gold Member

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            Any of these should work fine. If these leak under the cap I would go to the rad shop and make sure the filler neck is correct for the application

            View attachment 1715782164 [/QUOTE]


            Only out drip tube and not while running or under pressure. Only when engine is shut off and heat soaks. Pressure goes up and it dribbles till it cools down a bit.
             
          • Dana67Dart

            Dana67Dart The parts you don't add don't cause you no trouble FABO Gold Member

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            You are fine.

            You could remove a few cups of coolant to lower the level to about 1 inch below the filler inlet.

            Basically with a non recovery system. After all the air is expelled from the system (a few heat cool cycles) as the fluid expands as it gets hot it will raise the pressure of the coolant to 13 lbs, any pressure over that will be released by the rad cap. Assuming the coolant is filled to the top some coolant will also come out.

            When it cools and the coolant contracts, air will come back in. After a few cycles like this (assuming you never get the engine any hotter than the last time coolant dribbled out) you should not have anymore coolant dribbling out.

            The system is actually designed to NOT be filled to the top. There should be an air gap (about an inch) below the bottom of the filler neck.

            In a recovery system...

            The coolant is filled to the top of the radiator, full. The hose goes to the bottom of a recovery bottle, there is another hose from the top of the bottle to atmosphere.

            The bottle gets about 1/2 full with coolant.
            As the coolant gets hot in the radiator it expands, creates pressure in the cooling system and since the rad is 100%full the excess coolant goes into the recovery bottle. ( You can see this happen when the level in the bottle goes from "cold" to "hot" marks on the side of the recovery bottle.)

            When the engine cools the coolant contracts and pulles fluid back in from the recovery bottle.

            If you have a hole in or a loose fitting tube from the rad to the recovery bottle the fluid will not get pulled (yes I know atmosphere actually pushes the fluid) back into the rad.

            Hope that helps.

            By the way, I do recall now, WAY back in the day rad caps did not have the larger washer just under the cap, that was added for recovery systems BUT will not effect the function of the non recovery system.


            As to 2 types of caps, these days there are vented caps the type with the lever, to make removing a hot rad safer, ( just let it cool) and the standard cap that justs twits on and off. BUT both caps work the same way and will work fine on either type of system.


            One last thing if you always loose some coolant out the tube, than you might have other issues like head gasket leak or crack in the block, adding combustion pressure to the system and forcing fluid out. ( Like blowing water out of a straw)
             
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            • toolmanmike

              toolmanmike Moderator Staff Member FABO Gold Member

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              No actually the pressure goes down, the coolant boils at a lower temperature and that's when it dribbles. 1# of cooling system pressure will raise the boiling point 3°. You loose pressure (15#) and you are back to water boiling at 212° (depending on coolant strength and altitude)
               
            • SGBARRACUDA

              SGBARRACUDA ROY FABO Gold Member

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              Beat me to it. The fill level needs to be down about an inch. Or as I do, let it bleed off the excessive amount. It will stop the bleeding off of the fluid. My 69 Dart does the same.
               
            • Dana67Dart

              Dana67Dart The parts you don't add don't cause you no trouble FABO Gold Member

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              The pressure in the cooling system stays at 13 psi (engine on or off) till the coolant is cool enough to start to contract and either suck air or coolant from a recovery bottle back in behind it.

              I agree as it is cooling it gets below the pressurized boiling point of the coolant at 13 psi, but then it cooles to be below the boiling point of the coolant at 12psi etc till it is room temp and atmospheric pressure.

              I have never seen a cooling system overheat and boilover after shutdown unless there was some other problem, like a leak, trapped air etc.
               
            • toolmanmike

              toolmanmike Moderator Staff Member FABO Gold Member

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              My point exactly.
               
            • Syleng1

              Syleng1 Karma is real and Life is short... FABO Gold Member

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              I don’t know- toolmanmike- show me a picture of your radiator cap and what you run? I went with #14lbs but see my Demon340 is #16. Maybe I’m just too low. I cannot find the factory cap pressure for my altitude which is just about sea level or like 70ft above. I’m used to #16 or #18 but the radiator had a #14 on it before the rebuild with no issues.
              Damn “Flat Earth people” must be right.
               
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              • Tooljunkie

                Tooljunkie King of cobble/master of the broken bolt FABO Gold Member

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                The old style caps, as in the 70’s and maybe 80’s had a valve in them. Allowing no pressure buildup unless there was a surge or coolant rises enough to close it. The theory was to minimize pressure buildup when not necessary. Helps with lifespan of cooling system.
                If i could find the article i would post it here. It may have been in a service manual.

                The older rads will expel coolant until they find the happy medium. Will dribble some on extremely hot days.
                 
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                • SGBARRACUDA

                  SGBARRACUDA ROY FABO Gold Member

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                  That has been my experience with the older cooling systems.
                   
                • Mattax

                  Mattax Just the facts, ma'am FABO Gold Member

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                  One place that appeared was in a Chrysler tech bulletin.

                  edit. Found it.
                  upload_2021-6-17_21-29-59-png.png
                  upload_2021-6-17_21-31-10-png.png

                  upload_2021-6-17_21-32-19-png.png
                  upload_2021-6-17_21-33-52-png.png

                  from the 1968 Master Technicians Service Conference 68-10 Engine Temperature Control. (pdf)
                   
                  Last edited: Aug 16, 2021
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                  • pishta

                    pishta I know I'm right....

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                    Never have a rad boil over after you flip the safety lever? I have and it filled the overflow bottle faster that you say "holy sh!t" Flipping the lever pulls up the lower seal off the neck and depressurizes the rad, and like Toolmanmike stated, it'll boil when the pressure is released if its over 212 at sea level. Its called a safety cap as the main gasket never moves, containing all the boiling coolant to the neck of the rad and the poor overflow tube and catch bottle or your toes.
                     
                  • pishta

                    pishta I know I'm right....

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                    With that pic finally coming over, the explanation still seals the pressure in the rad until it can be mechanically vented to the overflow tube. Interesting.....
                     
                  • RustyRatRod

                    RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                    Posts #6 and #11 both bring up the often overlooked point to not fill the radiator completely up. It needs some room for expansion.
                     
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                    • Syleng1

                      Syleng1 Karma is real and Life is short... FABO Gold Member

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                      ThNks Guys for the overwhelming info on a radiator cap.

                      My short answer is I am filling it too much. Being a new engine I’ve been monitoring the levels like a hawk. So I forgot after 35 years of MoPar life that you need to let them find their level. I still have an empty quart bottle on the overflow for the Demon to meet track rules to catch the over flow. I’ve never touched it. So no coolant on the ground. Looks like heck but it works. Thanks for the help everyone!
                       
                    • toolmanmike

                      toolmanmike Moderator Staff Member FABO Gold Member

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                      Exactly. If you over fill it, it will puke and then stop. It found it's level.
                       
                    • Dana67Dart

                      Dana67Dart The parts you don't add don't cause you no trouble FABO Gold Member

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                      That is an interesting tech artical.

                      Had no idea they ever did that. I always thought the hanging center was a broken cap.

                      As to pressurize or not. I'll take my chances with pressurizing. It seems illogical to think that after you have started to boil the coolant you would start to pressurize it.

                      But I'm no cooling system engineer.
                       
                    • Mattax

                      Mattax Just the facts, ma'am FABO Gold Member

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                      Tech Sez: Ha Ha. Fooled ya!
                      left-jpg.jpg
                       
                    • RustyRatRod

                      RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                    • Tooljunkie

                      Tooljunkie King of cobble/master of the broken bolt FABO Gold Member

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                      Then there is living here in frosty canada, weak antifreeze mix and rad will freeze. Open cap and overheated engine will blow coolant like a geyser! Buddy got it right in the face, as he wanted to see in the rad, did it before we could stop him. It wasnt good.
                      Towel or rag to open and very slowly.
                       
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