Lower PSI rad cap??

[triple_green]

68 Charger 383 HP 22" auto

My original part number radiators has failed again after only about 3.5 years. It was totally redone about 8 years ago.

The radiator guys wants me to run a lower PSI cap 7-8, I was using an OE style 13 PSI cap.

Can anyone explain the physics/reasoning behind this?

Thanks!
Mark
,

[birdsandbees]

How did it fail, the core itself or his soldering work?

[flyinlow]

Increasing the pressure on the cooling system increases the boiling point about 2 degrees F. per PSI  for straight water. Not sure if it is the same number for water/antifreeze mix but still probably helps.

I run an eight PSI cap on aftermarket aluminum radiators . Less stress on the radiator and hoses. Never have problems. They do have higher cooling capacity than stock radiators however.

If you have localized hot spots in the engine the factory pressure might help prevent localized boiling.

[triple_green]

failed: tank seams and blow the outlet.

[birdsandbees]

Find a new rad guy! The old guy that just did my Bee rad (as his son brought him in out of retirement to do so) also did the incorrect rad I had  in the car back in 1988 . It is still totally serviceable and looks like it was recored a few months ago, not 30 years ago. I only removed it as I was able to find the correct 053 rad for my car.

[flyinlow]

I assume your engine runs well? No leaking head gasket or overheating issues producing large amounts of steam over loading the caps ability to release pressure. This could cause the radiator to fail.

  x 2,find a better radiator shop.

[c00nhunterjoe]

Poor rebuild. Find a new shop. Modern cars running plastic/alum crimps are in the mid to upper 20s now. 

[375instroke]

Where did you go?  One of my original 053 radiators is at Seattle Radiator Works right now fixing the seam I keep resoldering, and the damage from the fan clutch explosion.

http://www.dodgecharger.com/forum/index.php/topic,129049.msg1606298.html#msg1606298

[triple_green]

Peter all the radiator shops in the south end seem to be gone,

I had the guy a NW Radiator Works  in Tacoma make me a completely new one in 2011 or so. This is the second time back. in that time. This is the shop I am dealing with.

Any suggestions would be welcome. I am trying to stay with the old 045 top for the look of originality as this is how the rest of my engine compartment has been maintained.

Mark

[metallicareload99]

Increasing the pressure on the cooling system increases the boiling point about 2 degrees F. per PSI  for straight water. Not sure if it is the same number for water/antifreeze mix but still probably helps.

I run an eight PSI cap on aftermarket aluminum radiators . Less stress on the radiator and hoses. Never have problems. They do have higher cooling capacity than stock radiators however.

If you have localized hot spots in the engine the factory pressure might help prevent localized boiling.

  How often does a radiator cap pop tho?  You have a good point about preventing localized boiling with pressure, but assuming (which, based on the threads around here is a big assumption to make) the cooling system is functioning properly the radiator cap should never open?  Wouldn't a few psi work just as well as a few hundred psi?

I've been using a 7007 cap for the reasons mentioned above.  Murray brand part number 7007 is a 7 lb cap that should work, although it might not look factory correct 

[flyinlow]

If you have a good running engine and a healthy vintage cooling system with some air space in the top of the radiator, there should not be any coolant venting. Does it vent air when the cap hits its rating? I assume it does.

I use a reservoir return set up like modern cars so the radiator is full and as the system warms up some coolant goes into the reservoir ,causing its level to rise, then returns to the radiator on cool down.

50/50 coolant mix boils at 234* F according to the antifreeze bottle if you drove around with the radiator cap off or loose. A 13 lb. cap adds 26* F  for a 260* F boiling point with the cooling system fully pressurized.

It would be interesting to talk to a Chrysler Engineer from the 1960's  and find out why they used pressure caps and why 13-15 psi?

[alfaitalia]

Probably for the reasons you say....to raise the boiling point. Always better to have a bigger safety margin if you are building a car for a wide range of climates.....might of stopped a few warranty claims as well. Wont matter where I live.....but might if you are driving across the desert in Arizona or similar.

[375instroke]

Peter all the radiator shops in the south end seem to be gone,

I had the guy a NW Radiator Works  in Tacoma make me a completely new one in 2011 or so. This is the second time back. in that time. This is the shop I am dealing with.

Any suggestions would be welcome. I am trying to stay with the old 045 top for the look of originality as this is how the rest of my engine compartment has been maintained.

Mark

Got the radiator back from Seattle Radiator Works.  It's together.  It doesn't leak.  They put a 7psi cap on it, too.  The last radiator shop I went to did that, also.  I've never had overheating issues with the stock 053, 22" radiator with stock 440/727.