Re: [Chrysler300] Radiator cap pressure 300C
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Re: [Chrysler300] Radiator cap pressure 300C





Another aspect of this hot spot theory might interest those in this discussion . 
When I was involved with high power metal anode radio transmitting tubes as in 100 kW ( Machlett labs) , they used steam cooling  at essentially atmospheric pressure on the real big ones . It was something like 3 x (?guess from memory) more capable than water because the boiling process is factually carrying away heat faster than direct water immersion , in terms of btu removed at the interface . The power rating increased over water. It was called vapor cooling  This is due to added  heat needed to change water to steam .the steam went to a higher up steam radiator .  No pumps . This has the beneficial aspect Of removing  heat the most from the hottest places , so the max temp is known . If boiling happens at 241 , due to pressure , no surface is hotter than that, or else pressure would rise higher and open the cap . It re condenses to water ,yes , locally, in a car and that can be sudden and cause cavitation shock events and very unhappy implosion noises . ( steam radiator bang!) But need distilled water and even then  deposits were the problem 
As far  as reading 241,   I am suspect of radiator condition or ability ? Too hot . 
I once had a 57 D500 dodge with a blown head gasket. I had no $ , drove it 6 months in college with no 
Radiator cap . It never boiled driving around town and it was relatively new. (3 years old)so radiator very good. I did this with only water to avoid anti freeze in the oil due to cap pressure (embossed  steel shim  gaskets they used oem on hemi were junk.. they rusted at water holes to cylinder ) . It survived . 
Another PE ( EE)--  who defers to the brother 
 ME (!) , on boiling, but something like this goes on .
By the way in my experience the most stress comes in the 5 minutes after you shut off, if after a high load run . That is when cap opens . Probably due to local boiling as Rich describes and no new cooler water . I'd rather lose a pint once a year than run 14 psi. But that never happens if a good radiator . On our cars what does blow is the ranco heat  valve rubber . Soaks your passenger side interior in steam and antifreeze , and yes my upper tanks cracked too . good subject ! New radiator is big bucks but way to go.. I do not think rodding  or cleaning out gets you there.  
John G 

Sent from my iPhone

On Oct 18, 2017, at 2:25 AM, Rich Barber <c300@xxxxxxx> wrote:

Keep in mind that most boiling, if any, will occur in hot spots in the heads or block.  Even though the coolant in the radiator and hoses may not be boiling, it very well may be boiling at the hot spots around the exhaust valves.  The higher pressure radiator cap will enable the temperature to rise during heavy load/high ambient without the entire coolant load boiling.  The higher pressure will suppress boiling at hot spots.

 

BTW, from a heat exchange standpoint, those liquid to air heat exchangers behind the grilles of our 300’s (and other lesser vehicles) are more convectors than radiators. That’s why those HEX work so well when the car is moving and airflow across and through them is high.  My 300’s do not like a parade.  Added electric fans = more air flow at low speed over terrain.

 

The point made that restricting the differential pressure between inside the radiator to the atmospheric pressure will reduce thermal and mechanical stress on all elements of the system is valid.  The radiator portion of the system is designed to hold this pressure with a significant safety pressure unless it is damaged by corrosion or impacts.  If your trips don’t expose your car’s cooling system to heavy loads and/or high ambient temperatures and/or slow traffic speeds you might extend the service life of the radiator by using a lower pressure cap.

 

Finally, an internal combustion engine will be more efficient when operating at higher temperatures.  Newer engines are designed to run lean and hot all the time in order to maximize efficiency and reduce “pollutants”.

 

Lecture concluded.  Take out yellow paper and number 1-10. Prepare for a pop quiz.

 

Rich Barber, Professional Engineer Emeritus, BSME

Don’t think about how that is abbreviated.

Thankful that the fire fighters are getting control over the fires and that the loss of lives won’t be in the hundreds—even as another fire broke out south and west of us in the Santa Cruz mountains, way south and west of Brentwood and near Sausalito—at the north end of the Golden Gate.  A little rain may come tomorrow night and it will be welcomed.

 

From: Chrysler300@xxxxxxxxxxxxxxx [mailto:Chrysler300@xxxxxxxxxxxxxxx] On Behalf Of 'John L. Chesnutt' chesnutt@xxxxxxxxxxxx [Chrysler300]
Sent: Tuesday, October 17, 2017 7:52 PM
To: 'Henry Schleimer' <henry.schleimer@xxxxxxxxxxxxxxx>; 'Larry Jett' <LarryWJett@xxxxxxxxx>; 'John Grady' <jkg@xxxxxxxxxxxxxxxxx>
Cc: 'chrysler300@xxxxxxxxxxxxxxx' <Chrysler300@xxxxxxxxxxxxxxx>
Subject: RE: [Chrysler300] Radiator cap pressure 300C

 

 

Hi,
I have always used a 14# cap and have had no problem for the last 59 years we have had our 1957 300C. Several years ago I finally put a new core in the radiator as the tubes looked like they were leaking. The replacement was a four tube vs the original three tube. The shop that I use said he could not get a three tube from his suppler. A 7# cap is ok, but I would rather not lose any water when driving at high speed on hot days. The four tube took about a half gallon more water than the original.

John

-----Original Message-----
From: Chrysler300@xxxxxxxxxxxxxxx [mailto:Chrysler300@xxxxxxxxxxxxxxx] On Behalf Of 'Henry Schleimer' henry.schleimer@xxxxxxxxxxxxxxx [Chrysler300]
Sent: Tuesday, October 17, 2017 7:06 PM
To: 'Larry Jett'; 'John Grady'
Cc: 'chrysler300@xxxxxxxxxxxxxxx'
Subject: RE: [Chrysler300] Radiator cap pressure 300C

241 degrees is about 6 psi with the 50% coolant mix that I use. The radiator guy also said there are 10 and 13 psi caps available.

Cheers Henry

From: Chrysler300@xxxxxxxxxxxxxxx [mailto:Chrysler300@xxxxxxxxxxxxxxx] On Behalf Of Larry Jett LarryWJett@xxxxxxxxx [Chrysler300]
Sent: Wednesday, 18 October 2017 11:15 AM
To: John Grady
Cc: Henry Schleimer; chrysler300@xxxxxxxxxxxxxxx
Subject: Re: [Chrysler300] Radiator cap pressure 300C

Can't speak to the 57 radiators, but on the way to the New Mexico meet, our 63 300 sport indicated 241 degrees on my Dakota Digital heat gage and nothing blew on the way up the Grapevine in 105 ambient. Using the 14 pound cap.

Eat, Drink, and be Larry........

On Tue, Oct 17, 2017 at 5:41 PM, John Grady jkg@xxxxxxxxxxxxxxxxx [Chrysler300] <Chrysler300-noreply@xxxxxxxxxxxxxxx> wrote:

I agree with that 100% . Smart guy

Sent from my iPhone

On Oct 17, 2017, at 7:47 PM, 'Henry Schleimer' henry.schleimer@optusnet.comau [Chrysler300] <Chrysler300-noreply@xxxxxxxxxxxxxxx> wrote:

Poked a small hole in my radiator and took it a radiator shop yesterday to get soldered. While there I asked for a new 14 lb radiator cap. The owner said I didn’t want one that high and recommended a 7lb cap. After I said that 14 was the factory spec he said he was aware of that BUT for the old style large tank radiators the pressure is too high making them crack along the top seam. The difference in temp is not that great but the stress in the solder is much reduced. He said if you get over 100 C your have problems with your system anyway.

I then remembered my parents’ 67 Valiant which had the same top tank design and recalled we must have had the top tank resoldered about 4 times in its life. I said I had never heard a radiator guy recommend a lower cap pressure. He said it was funny that! He also said if I fitted a 7 lb cap he wouldn’t see me for the next 20 years!

To reinforce the issue of the big top tank having a flex problem, he pointed out the bottom smaller tank usually never cracks. It all started to make sense.

I know this may generate many opinions but I’m willing to give it a try. I thought I might pass this on to people who have the same problem with tanks cracking in an otherwise ok cooling system.

If I don’t have any cooling problems at the lower pressure, there is no need to put extra stress on the system. Better the cap lets go rather than the radiator, hose, block plug etc. If it keeps losing too much water, I can always go up in pressure.

Cheers

Henry

[Non-text portions of this message have been removed]

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Posted by: "Henry Schleimer" <henry.schleimer@xxxxxxxxxxxxxxx>
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Posted by: John Grady <jkg@xxxxxxxxxxxxxxxxx>


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