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After my scare last friday with the freeze plug blowing out we removed the radiator cap that was 16 or more pounds and installed a 7 pound cap. I noticed Summit sells zero and 4 pound caps.

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You dont need any pressure UNLESS you have a over heating
issue

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After my scare last friday with the freeze plug blowing out we removed the radiator cap that was 16 or more pounds and installed a 7 pound cap. I noticed Summit sells zero and 4 pound caps.

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You dont need any pressure UNLESS you have a over heating
issue

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Exactly
The cap Lbs rating is simply keeping the water from boiling. Example a 13lb cap @ 252 degree boiling point, and 18 lb @ 270 degree. 16# would be fine @ 258 degrees.
As temp goes up so does pressure, giving in the same volume via cooling system. It will keep the water from boiling, but the added pressure can cause engines to leak in area's like head gaskets or any other weak area's that cant hold the pressure. That's why most race only cars run 8-10# caps. And you will see modern cars with much higher caps cause they run such near the actual boiling point of water now, newer cars and trucks run 210 deg + now. Water boils at sea level 212 deg. People at high alt around the world have actual trouble cooking some things like we normally do and use pressure cookers for normal things we cook in a open pot. Only time we use a pressure cooker is when we can veggies etc.
Bla
Bla Bla

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Thanks, I think I'll try the 4 pound cap. The car doesn't run hot, and I'm not sure why that freeze plug blew out, but I'm thinking less pressure in there won't hurt.

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I bet pressure had nothing to do with it. something flexing or plugs not installed deep enough.

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Bob, I feel its a good idea to use a higher psi cap to help prevent the water from boiling.

Once it boils, the pressure can sky rocket.

If your having heating issues that are causing the pressures to rise enough to blow out a freeze plug, lowering the cap pressure will allow your current system to boil over sooner. Witch will disperse that excess presure into your overflow reseveware, if it can handle all of it.


IMO, stick with the higher pressure cap and fix any over heating or loose freeze plug issues. mike

Reducing radiator cap pressure is just asking for boil over problems on our hot running race/street cars.

Extra cap pressure rating is a good thing IMO. mike

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I run a 16lb cap

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Run the highest cap pressure your radiator and gaskets will stand.
The first place water boils is inside the head, at the exhaust seat and spark plug - even if your gauge still shows 180°. When this happens, the steam formed at the metal surface prevents water from touching the metal, and it just gets hotter. The steam can't transfer any heat - it's not dense enough. Result: the engine knocks.
Increasing the pressure raises the local boiling point a lot.
How is this different from just running 50/50 anti-freeze to raise the boiling point? 50% antifreeze only transfers heat at 1/2 the rate of water.

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Interesting stuff, my car doesn't run hot. When the freeze plug blew out it was only at 170 degrees or less. I just figured that whatever happened may be prevented by a lower pressure cap. That freeze plug shot out like a cannon, made a loud BANG that I heard over the engine at full song. By the looks of the plug, it was more than likely installed wrong.

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Interesting stuff, my car doesn't run hot. When the freeze plug blew out it was only at 170 degrees or less. I just figured that whatever happened may be prevented by a lower pressure cap. That freeze plug shot out like a cannon, made a loud BANG that I heard over the engine at full song. By the looks of the plug, it was more than likely installed wrong.

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