Moparts

How much pressure is needed in cooling system?

Posted By: ProSport

How much pressure is needed in cooling system? - 09/25/10 02:57 AM

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.
Posted By: MR_P_BODY

Re: How much pressure is needed in cooling system? - 09/25/10 03:18 AM

Quote:

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.



You dont need any pressure UNLESS you have a over heating
issue
Posted By: Bob_Coomer

Re: How much pressure is needed in cooling system? - 09/25/10 03:42 AM

Quote:

Quote:

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.



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



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
Posted By: ProSport

Re: How much pressure is needed in cooling system? - 09/25/10 03:53 AM

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.
Posted By: Quicktree

Re: How much pressure is needed in cooling system? - 09/25/10 04:03 AM

Quote:

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.

I bet pressure had nothing to do with it. something flexing or plugs not installed deep enough.
Posted By: Sport440

Re: How much pressure is needed in cooling system? - 09/25/10 04:13 AM

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
Posted By: Quicktree

Re: How much pressure is needed in cooling system? - 09/25/10 04:15 AM

Quote:

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

I run a 16lb cap
Posted By: HEMIFRED

Re: How much pressure is needed in cooling system? - 09/25/10 04:40 AM

When I run Evans Coolant it doesn't boil until 370 degrees so only zero cap
Posted By: polyspheric

Re: How much pressure is needed in cooling system? - 09/25/10 04:57 AM

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.
Posted By: Chad Bittle

Re: How much pressure is needed in cooling system? - 09/25/10 05:38 AM

I'm glad you asked this question. Lots of stuff I had no idea...
Posted By: ProSport

Re: How much pressure is needed in cooling system? - 09/25/10 05:42 AM

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.
Posted By: jcc

Re: How much pressure is needed in cooling system? - 09/25/10 07:54 AM

Quote:

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.



I agree, pressure has few downsides, but poorly seated freeze plugs do.
Posted By: moparniac

Re: How much pressure is needed in cooling system? - 09/25/10 11:25 AM

Bob I had a freeze plug blow out on me one time also in my challanger leaving a garage hammering on it down the street! I now have screw in freeze plugs though

I have heard of people dying from that going down the track from that happening!

old archived pic!
Posted By: mac56

Re: How much pressure is needed in cooling system? - 09/25/10 12:19 PM

Quote:

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.


If a freeze plug shoots out like a cannon I would have to think there is something else going on. I run a 22 lb. cap for the reason stated early about steam forming around center exhaust ports.
Posted By: tonycpe

Re: How much pressure is needed in cooling system? - 09/25/10 02:01 PM

Do most engine builders stake the freeze plugs?
Posted By: 340B5

Re: How much pressure is needed in cooling system? - 09/25/10 04:25 PM

As said above, no pressure is needed. Every one lb. pressure increase raises the boiling point 2 degrees.

Evans coolant?
Posted By: Womanator

Re: How much pressure is needed in cooling system? - 09/25/10 04:39 PM

We run Evans coolant in are Semis because of it not having any water in it and boiling point is above 380 degrees.

But we just got a bulletin from Evans to start using a 3lb cap.
Posted By: Locomotion

Re: How much pressure is needed in cooling system? - 09/25/10 04:47 PM

Quote:

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.



A blown head gasket can often cause overheating. But even if yours was not, it wouldn't hurt to go through the tests for a blown head gasket including watching for bubbles in a cool or warm, full radiator while running with the cap off.

Get much water in your overflow bottle?
Posted By: Crizila

Re: How much pressure is needed in cooling system? - 09/25/10 10:22 PM

Evans Coolant? Anyone have info on it? Make up, NHRA legal, where to buy? Thanks.
Posted By: polyspheric

Re: How much pressure is needed in cooling system? - 09/25/10 11:25 PM

Evans has an interesting idea (can't boil at any temp found in the water system), but it's only about 65-70% as effective at removing heat from the jacket surfaces.
If you still have local boiling-induced knock at 250°F (15 lb. cap, pure water) Evans will help with the boiling but the engine will operate at higher temperature unless you increase the water transfer rate, radiator size, air volume through the core, etc.
It's also about 10 × as viscous as water, so the pumping load is higher (even with no cap, there's pressure inside the engine).

Summary: if you have a cooling problem Evans won't help since the engine temp will go up. The "tests" showing the Evans is cooler than the water it replaced as it exits the engine is simple: it's absorbing less heat.
If you can't control knock with water and a pressure cap, it will fix that (but the temp will go up).

There's also a cost problem:
Water is free, plus a pressure cap, and you can get more anywhere.
Evans is over $100 to fill (but permanent), you should still run a cap (it smells bad).
Posted By: jamesc

Re: How much pressure is needed in cooling system? - 09/26/10 01:00 AM

Quote:

Run the highest cap pressure your radiator and gaskets will stand.




this is the correct answer to the OPs question
© 2024 Moparts Forums