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Conference ssdevo::4wd

Title:4 Wheel Drive
Notice:Welcome to 4WD's new home! = 399
Moderator:TARKIN::LINMAN
Created:Fri Mar 13 1987
Last Modified:Fri Jun 06 1997
Last Successful Update:Fri Jun 06 1997
Number of topics:1639
Total number of notes:30449

1634.0. "Radiator Cap Question - 13lb, 16lb?" by BSS::G_MCINTOSH (Touch Not the Cat, Bot the Glove) Fri Feb 07 1997 17:05

    
    I went to Ford parts dept to replace my radiator cap.  I took my old
    one in with me, which was a 13 lb cap.  The parts guy gave me a new
    one which is 16 lbs.  The old cap has been replaced for my specific
    vehicle to the new cap with a different rating.
    
    What does this number mean on a radiator cap?  What does it do?
    Doesn't it just seal the radiator and allow the coolant to flow?
    
    Stupid questions probably, but you gotta start somewhere.
    
    Thanks.....Glenn
    
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1634.1It's PSIHSOSS1::HARDMANIt's a girl! Now what?Fri Feb 07 1997 18:0715
    Glenn, the number denotes the Pounds Per Square Inch of pressure that
    will accumulate within the cooling system before the spring loaded seal
    in the cap will open and allow the excess pressure (steam and water) to
    escape via the overflow tube.
    
    At 16 PSI, your new cap will release the excess pressure. All modern
    automotive liquid cooling systems are pressurized. The boiling point of
    water (and water/antifreeze mixtures) rises as pressure increases.
    
    Ford may have had some problems with engines overheating with the 13 lb
    cap and made an unannounced change to the 16 lb model. I doubt that the
    16 lb. cap will harm your radiator.
    
    Harry
    
1634.2Thanks Harry.BSS::G_MCINTOSHTouch Not the Cat, Bot the GloveSat Feb 08 1997 03:3419
    
    Thank you Harry for your explanation.  I hope this was the right forum
    in which to ask this question.  I noticed that the notesfile Mechanix_3
    is no more.
    
    Let me see if I understand.  At 13 PSI the engine may have overheated
    too easily, so in an effort to prevent this, Ford wanted to raise the 
    boiling point of the coolant mixture, and in order to do this, they 
    increase the PSI of the radiator cap because the boiling point of
    water (and water/antifreeze mixtures) rises as pressure increases.
    
    Is this correct?  If so, it makes alot of sense.  
    
    One more, if I may....why are automotive cooling systems pressurized?
    What do I care as long as the coolant mixture goes around and around,
    cools the engine and then gets cooled in the radiator, etc?
    
    Thanks.....Glenn
    
1634.3ThanksBSS::G_MCINTOSHTouch Not the Cat, Bot the GloveMon Feb 10 1997 12:227
    
    Nevermind....I got it Harry.  I understand now.  Thank you.
    
    Glenn
    
    
    
1634.4Ol' faithful?HSOSS1::HARDMANIt's a girl! Now what?Mon Feb 10 1997 20:248
    Glenn, it makes a big difference to you. Isn't BSS in Colorado? Water
    boils at a lower temperature at high altitude, plus the less dense air
    doesn't cool the radiator as well. But the engine still reaches temps
    of 210 degrees F or higher, because of the thermostat that's installed
    in it. You'd be boiling over on every hill climb. :-(
    
    Harry
    
1634.5Thank YouBSS::G_MCINTOSHTouch Not the Cat, Bot the GloveTue Feb 11 1997 13:395
    
    	Harry, I understand now completely.  Thanks for the lesson.
    
    	Glenn