radiator cap pressures

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  • July 30, 2009 05:27 PM - 7165 Views
    I know radiator caps come in different pressures. Can someone explain how to determine what ones needs for proper cooling etc. Thanks. RAF

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  • Comments
  • sedanbob Rides Info - saint louis, Missouri
    July 30, 2009 08:30 PM

    Your radiator will be rated at a certain pressure - Walkers are rated at 15 to 18 pounds.  You could use a cap rated at 15 pounds.  Using a cap rated higher than the radiator may cause the radiator to fail.  You could use a cap rated for less pressure (like 7 pounds).  The pressure raises the boiling point of your coolant, the more pressure, the higher the boiling point (to a point).  Some racing radiators are rated at 29 pounds allowing them to use a higher pressure cap.  That shouldn't be necessary in a streetrod (unless you decide to race your streetrod at the circle track ).  I am in the process of asking the AFCO folks what mine is rated at.  (I checked the websites for AFCO and Griffin, but couldn't find any figures.)  Hope this helps. 

  • REBORN55 Rides Info - de soto, Illinois
    July 30, 2009 08:40 PM

    Radiator caps usually raise the boiling point 3 degrees per lbs. of pressure--what I was taught

  • Mike52 Info - lutz, Florida
    July 30, 2009 08:48 PM

    On the PRC radiator I recently got, they recommended a 16lbs cap.


  • ezstreet Rides Info - noblesville, Indiana
    July 30, 2009 09:12 PM

    Here's my street smarts....and school of hard knocks. Water boils at 212 deg and a 50% ethylene glycol and 50% water boils at 225 deg. Like Reborn55 said, for each 1 pound the cap is rated it will increase the boiling point by 3 deg. So a 15 pound cap will raise the boiling point by 45 deg and you will then have a boiling point of  around 270 deg. The object is to get the highest boiling point you can without doing pressure damage to the cooling system ie: the radiator ! If you lower the pressure cap rate, you will also lower the boiling point and actually cause a problem. I think by design that flathead V 8's use a 7 pound cap, but I use a Walker Radiator on a 350 sbc with a 15 pound cap....works for me.

  • rodek Rides Info - menifee, California
    July 31, 2009 12:40 AM

    this coolent EVANS  WATERLESS engine coolants I heard about it has Boiling point  375°F @ 0 psi  Freezes -40°F
    here is a link to their site http://www.evanscooling.com

    I don't know much about this stuff nor have I used  it if someone here knows anything about it please post it

  • raf Info - arlington heights, Illinois
    July 31, 2009 10:24 AM

    Thanks for the info. PRC sent a 16# cap for my recent radiator change. The old radiator had a 7# cap(nicely chrome plated) Engine ran @ 180-190 degrees then , Now with a 160 degree thermostat and engine fan moved closer to the radiator(radiator is thinner than the old one)with a spacer, the temp sits right at 160. On a hot day if I see temp rising over 160 I flip on the electric fan. Switch is on the panel-just my choice over an automatc turn on. BTW the electric fan sits in front of the A/C unit,radiator and trans cooler.

    I'm glad we got some good responses on this subject- we learn something every day. Thanks again.


  • Bill33 Rides Info - victoria b.c., Canada
    July 31, 2009 07:53 PM

    If your engine can heat the water up to 375 degrees......boiling and radiators will be the least of your problem.....

  • jimmothershead Rides Info - huntingtown, Maryland
    August 02, 2009 03:07 PM

    RAF.......16# on a Walker Cool Mate for 72,000 miles. 195* thermostat. Poluted '85 Iroc in our '33. This time of the year 85* to 90*,  runs 197* with air on the Interstate. In town at a light with air, drops down to 191*..........super.

      Ditto for all the other rods.

    What is your profile?


  • rodek Rides Info - menifee, California
    August 03, 2009 11:56 AM

    Bill33, the reason why i was looking at this product is that you can run it with 0 pressure cap and it supposed to prevent any hot spot in the block that vaporized the water in normal coolant not that I’m an expert in coolant or anything but to run with a 0 pressure system seems to me that would take a stress off the hoses lessen the chance of blown hose. A mechanic friend of mine recommends it he runs it in his diesel truck pulling his 5th wheel camper he said even with the air on fully loaded up hill it don’t get hot at all.

    I know that it is kind of expensive but I my give it a try.  

  • Bill33 Rides Info - victoria b.c., Canada
    August 03, 2009 06:19 PM

    I know I'm skeptical about all this stuff, but only because I think I tried everything on an engine that was giving me overheating trouble and in my opinion its all snake oil, not that it won't help to some degree, but if you're having overheating problems, they will never end until you cure the problem.  You can run with straight water (I wouldn't for all kinds of reasons) and 0 pressure cap and it won't boil till 212, or you can run with 50/50 antifreeze and 0 pressure and be good to 225, but like Ezee street says, you add another 3 degrees for each pound of pressure before it boils, so even a 7 lb cap will get you to 246, which should cover you in almost all cases.  The trouble with getting the boiling temperature up too high, you'll be melting gaskets before you know you have a problem.....but in the end, it's up to you......whatever makes you comfortable.

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