Let's Talk About Radiator Caps!
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Senior User
Joined: Aug 2012
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From: Ft. Worth
Let's Talk About Radiator Caps!
Hello All, For our IDI engines...What would be the correct radiator cap...a 7 lb, a 13lb, a 16lb, or ?
Seems to me...the higher the poundage the more pressure our cooling systems have to work at, thereby leading to more leaks if you have some weak spots...such as maybe head gaskets, old radiator, old hoses, weak clamps, etc...
I know the higher the poundage, the higher the temp the coolant has to reach before boiling...Wouldn't it be better to use a lower poundage cap and let the system utilize the overflow tank more as the fan kicks in to cool things back down and suck the coolant back into the radiator...and again...might this alleviate a lot of "where is all my coolant going" and "I can't find any leaks"...
Just thinking this out logically...Maybe I'm totally wrong...so what info or ideas do you guys have?
I am thinking og going to a 7 lb cap...
Seems to me...the higher the poundage the more pressure our cooling systems have to work at, thereby leading to more leaks if you have some weak spots...such as maybe head gaskets, old radiator, old hoses, weak clamps, etc...
I know the higher the poundage, the higher the temp the coolant has to reach before boiling...Wouldn't it be better to use a lower poundage cap and let the system utilize the overflow tank more as the fan kicks in to cool things back down and suck the coolant back into the radiator...and again...might this alleviate a lot of "where is all my coolant going" and "I can't find any leaks"...
Just thinking this out logically...Maybe I'm totally wrong...so what info or ideas do you guys have?
I am thinking og going to a 7 lb cap...
Mountain Pass
Joined: Aug 2012
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Factory correct is 13 psi, that's whats on my truck. Lowering pressure lowers boiling point and that's not good if you do any towing. You could convert to Evans waterless and run a 0 psi system. Expensive but worth it.
Fleet Owner
Joined: Jul 2006
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From: Mi'kma'ki
13 lb caps for the idi like stated.
id just swap it out if i where you.why risk blowing a head gasket for such a cheap and easy part to replace right? may not have issues...yet.but post back if you blow a gasket in the future,or something else comes up for everyone.people running ELC coolant i doubt are posting about their failed water pumps either.
Posting Guru
Joined: Jan 2001
Posts: 1,101
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From: Poway, CA
13psi is factory, per the original cap on my truck I just replaced with a new OEM piece that says the exact same thing.
Running a cap lower than stock would be tempting fate IMHO, unless you're running some kind of coolant that has a much higher boiling point like the Evans.
Here's a spreadsheet that I keep running into every time I research anything coolant-related. I can't validate its accuracy, but it at least gives you a rough idea of the effect your cap pressure and your coolant mixture has on the boiling point:
http://www.heat-transfer-fluid.com/p...ling-point.pdf
FWIW, the Old Wive's tale I always heard about higher pressure caps is that they're hell on older copper/brass radiators but aluminum cores are more stout and can take the pressure.
Mike
Running a cap lower than stock would be tempting fate IMHO, unless you're running some kind of coolant that has a much higher boiling point like the Evans.
Here's a spreadsheet that I keep running into every time I research anything coolant-related. I can't validate its accuracy, but it at least gives you a rough idea of the effect your cap pressure and your coolant mixture has on the boiling point:
http://www.heat-transfer-fluid.com/p...ling-point.pdf
FWIW, the Old Wive's tale I always heard about higher pressure caps is that they're hell on older copper/brass radiators but aluminum cores are more stout and can take the pressure.
Mike
Fleet Mechanic
Joined: Jun 2009
Posts: 1,320
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From: CT
both are incorrect though.
13 lb caps for the idi like stated.
id just swap it out if i where you.why risk blowing a head gasket for such a cheap and easy part to replace right? may not have issues...yet.but post back if you blow a gasket in the future,or something else comes up for everyone.people running ELC coolant i doubt are posting about their failed water pumps either.
13 lb caps for the idi like stated.
id just swap it out if i where you.why risk blowing a head gasket for such a cheap and easy part to replace right? may not have issues...yet.but post back if you blow a gasket in the future,or something else comes up for everyone.people running ELC coolant i doubt are posting about their failed water pumps either.
The radiator cap increases the boiling points. It's like sticking water / antifreeze at a higher elevation. I remember seeing a chart somewhere but, the pressure makes a big difference.
Elder User
Joined: Mar 2008
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From: Marianna, Florida USA
You need 2 things to prevent cavitation:
1. Proper SCA levels.
2. Proper pressure on the coolant.
1. Proper SCA levels.
2. Proper pressure on the coolant.
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Senior User
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From: Long Island, NY
FWIW I have a leaking head gasket I'll eventually replace it but for know it is external leak only and I go through very little water so I live with it. I went to a 7lb cap last month figuring I would slow my leak or stop it cause of the lower pressure. That lasted me about an hour. Truck was empty and I was driving easy she warmed up quicker and got much hotter. I pulled over once I hit 215 and let it idle for a few min while I checked for leaks. Got back in and I was at 220 shut it down replaced the 7lb cap with the 13lb one. For the rest of the day she never broke 190. Learned my lesson quick, book calls for 13 it gets 13. Sorry for the long post hope I can save someone from making my mistake. With out the aftermarket gauge I prob would have finished off my head gasket.
Fleet Mechanic
Joined: Jun 2009
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From: CT
ahh. I'm not too up to par with my boiling physics.
Postmaster
Joined: Feb 2011
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marianna beat me to it. pressure is critical to prevent cavitation. there's some uncertainty in this thread if its supposed to be 13 or 16 pounds, but i wouldn't touch anything less. now on a gasser, it doesn't matter much, as cavitation isn't an issue.
Posting Guru
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From: Poway, CA
Mike
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you mean for us or for a gasser? on a gasser, IF the temp never reaches its natural boiling point, you'll never be aware of a cap that doesn't seal. its only noticed when you exceed that temp and start steaming out.
Posting Guru
Joined: Jan 2001
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From: Poway, CA
In the end, I guess all I'm saying is that I don't think running lower pressure caps is a great idea, especially if all you're trying to accomplish is to mask potential problems that could otherwise be dealt with by proper maintenance.
Mike
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