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Author
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Topic: Why does radiator hose collapse?
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Fastback68
Gearhead Posts: 4511
From: Sucat, Paranaque, Philippines
Registered: Jul 99
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posted 01-22-2006 10:22 PM
 
I just witnessed this happening in dramatic fashion. We're testing a 351C with an old, softish lower rad hose with no wire reinforcement. Even raising the revs to 1,800 or so completely closes the hose a couple of inches from the block!
Can someone explain the physics of this to me?
Thanks,
Simon
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Ryan Wilke
Gearhead Posts: 3237
From: Stanton, Michigan, zip 48888
Registered: Oct 2000
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posted 01-22-2006 10:47 PM
Simon, It is a common condition for the suction of the water pump pulling water from the radiator toward the pump to collapse the lower hose. Your lower radiator hose should include a stiff coil spring wound inside it to keep the hose from collapsing.... Because the upper hose is pushing water from the pump to the radiator, it won't have this problem as it's under pressure; not suction. Since you apparently didn't get a spring with your new lower hose, take the spring out of your old lower hose and put it into your new lower hose. Not an uncommon condition when a fella is mixing and matching different radiators and trying to fit different hoses to it. You may need to trim the length of the spring as necessary. I've even pulled springs from some junkyard car lower hoses (same diameter hose) to use in another cars/hose when I needed one & didn't have one. Good Luck!
Ryan 
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Fastback68
Gearhead Posts: 4511
From: Sucat, Paranaque, Philippines
Registered: Jul 99
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posted 01-22-2006 11:32 PM
Yep, it seems to be particularly bad on the longer hoses - 71-3, compared with 67-8, for example, which are shorter.
I just wouldn't have thought the suction would be that great though. I mean, there's obviously air in the system, but to collapse the hose the suction must be so great that a partial (total?) vacuum is being set up.
Physics was my worst subject at school, which might be obvious 
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64coupe
Gearhead Posts: 173
From: Bristol, PA
Registered: Sep 2002
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posted 01-22-2006 11:40 PM
just buy a new hose and you should be fine....I don't even think they put springs in hoses now adays.
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trashline
Gearhead Posts: 2230
From: Levittown, Pa
Registered: Dec 2003
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posted 01-23-2006 12:20 AM
lol last night I went out for my final qualification on the engine at the firehouse. While im pumping the truck the guys shut the hydrant down on me. you want to hear noises the pump sucked the 5 inch diameter hose dry. my quick skills pulled the tank to pump valve and saved the truck. lol but yea springs are good. Ive gotten new lower hoses from stores without springs too.------------------
88 thunderbird TC 2.3L
Gillis at 18 psi, walbro 255 lph fuel pump, Kirban at 39 psi, 3.73 8.8" rear, rebuilt head, brand new IHI 66 mustang 200ci 3 speed
Holley weber two barrel, msd 6A, 3.5 gears, 3.03 v8 three speed trans. 68 Fairlane 289 w/ auto
rusting away motor is going in the mustang 79 f150 300 3 onda tree
awaiting a new transmission
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Fastback68
Gearhead Posts: 4511
From: Sucat, Paranaque, Philippines
Registered: Jul 99
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posted 01-23-2006 01:12 AM
Well, after extensive and painful research, it appears that there is a partial vacuum situation set up in a cooled engine's cooling system which is why they can recover coolant from an overflow tank.
It makes my brain hurt, but I believe that explains why a hose can collapse. If all the air within the cooling system were at atmospheric pressure, I don't think the suction alone could collapse it.
Don't listen to me! I'm an idiot  Dan Jones or one of those rocket scientists that hang out in the racing forum would know![This message has been edited by Fastback68 (edited 01-23-2006).]
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