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Old 10-10-2005, 04:36 AM
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Radiator cap pressure question

I have a custom made Howe's aluminum radiator. It says " Use 20-22 lb cap"
What affect? If any, would a 16 lb cap have on the cooling efficiency?
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Old 10-10-2005, 05:26 AM
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each pound of increase equates into a 3* increase of the boiling temp of water....so a 20 lb cap would put the boil over point somewhere around 272* or (212 + {3 x 20})
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Old 10-10-2005, 05:53 AM
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I prefer to use the lighter cap....That way, if it the cap releases, you know you are overheating. The idea of a higher boiling point is nice, but I still don't want to get that hot.
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Old 10-10-2005, 08:15 AM
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You would rather the water temp go up and still stay in the block than have the water boil out and creat severe hot spot's that crack heads or worse, a block. At least then, you have a chance to cool the engine rather then wait till it cools completely before adding water. That's when the cracks form.
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Old 10-10-2005, 10:50 AM
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Cap Pressure

Thanks guys for the quick replies. So, the efficiency of the cooling system is not bothered by the cap pressure?.16 lb. cap boil over about 260* the 20lb cap 272*??Wonder why they required a 20-22 lb cap in the first place?
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Old 10-10-2005, 12:03 PM
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wITH A 20# cap I sure hope all of your hose connections are tight, including the heater hoses and core, if you have one!
Just like a chain, only as good as the weakest link !!
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Old 10-10-2005, 08:57 PM
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It says 20-22# because it is a racing radiator. The newer aluminum stuff will hold those kinds of pressure but the old brass radiators will not. Normal street cars don't need that high of pressure...but it doesn't hurt. If you have an old brass heater core then do not put a 20+# cap on it because you will blow out the heater core.
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Old 10-10-2005, 09:12 PM
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Quote:
If you have an old brass heater core then do not put a 20+# cap on it because you will blow out the heater core.
I have found that this is the weak point in cars too. I always use an 8 to 10 lb cap.
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Old 10-10-2005, 10:41 PM
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Quote:
Originally Posted by Triaged
It says 20-22# because it is a racing radiator. The newer aluminum stuff will hold those kinds of pressure but the old brass radiators will not. Normal street cars don't need that high of pressure...but it doesn't hurt. If you have an old brass heater core then do not put a 20+# cap on it because you will blow out the heater core.
Not picking on you or anybody,

the serious question is...... If you put this humongous aluminum radiatior on it to cool it, why would the temperature get high enough to make the pressure go above 16 on up to 22 anyway???????

I thought it was suppose to run cooler not hotter with a BIG radiator....

Are you chasing a problem that does not exist???

oh ya, the Evans Coolant does not boil until 369 with no pressure, so why not spend another $ 35 and run it with a zero or 3 pound cap?
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Old 10-10-2005, 11:14 PM
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Quote:
Originally Posted by Triaged
If you have an old brass heater core then do not put a 20+# cap on it because you will blow out the heater core.
Excellent input all you guys. Thanks,

It is not the core construction, it is the condition. New manufactured brass heater cores accept 16 psi.

Any old partially corroded component could blow out. Old or cheapo hoses, corroded intake manifold gasket surfaces, etc.
As solidaxel said,,,, the weakest link..... poof.

I personally don't run more than 16 psi caps. And the only reason I run that much is to prevent heat soak after shut off from filling the puke tank to readily.

Oh ya, and test those new caps on a cap tester. MOST new caps will NOT hold their pressure.. usually 2-3 pounds less. I've tested a bunch of them. Maybe 1/10 is close. (So if you got a puker after shut off with your 14 cap, maybe it is only a 10)

Expensive race caps hold OK, they have been individually tested.
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