Re: [Chrysler300] Radiator cap pressure 300C

["Ray Melton rfmelton@xxxxxxx [Chrysler300]" <Chrysler300-noreply@xxxxxxxxxxxxxxx>]

Hello Henry -

I sure agree with Ron about adhering to the factory spec on radiator cap relief pressure - to my (admittedly somewhat limited) knowledge since the mid-sixties, essentially all foreign and domestic radiator cap relief pressures have been in the realm of 12 to 18 psig for at least the last 60 years or so,  which is why you will have a hard time finding a new cap with a 7-psig relief rating  because it will obviously lead to boiling at a lower temperature, with all the attendant problems that brings!   Indeed, my 1957 Factory Service Manual specifies a 14 psig cap (which I had a hard time finding in the absolute correct concours shape), so I went with a 16 psi cap, which has been no problem since the initial outing, where the cooling system decided to "burp" at least a pint of coolant onto the tarmac after a 30-mile trip the first time out of the shop after nearly five years of restoration!  Very bad manners!   Gauge didn't show overheat, and I was subsequently advised by other members that this is normal in a system with NO recovery bottle -- the system just dumps coolant overboard onto the pavement until the level gets to where "the system" says it should be!  It appears to be a self-regulating system, as the "burping" has not occurred since the first outing!  Temperature stays normal (although slow to rise - take ten minutes on road to show true temp!), and no "burping" any more.

Good luck with resolving your concern!

Ray Melton  Las Cruces, NM  1957 Chrysler 300C cvt  White/Gauguin  s/n 3N572517

(Side note:  My "Big Red" recently garnered "Best of Show", a  really nice  3-ft trophy and bottle of champagne at the big (112 entries) annual Lions Club car show in historic La Mesilla, New Mexico this last weekend - Oct 14 -- it's only the car's second showing after a nearly five-year restoration effort!)

On 10/17/2017 7:57 PM, 'Ron Waters' ronbo97@xxxxxxxxxxx<mailto:ronbo97@xxxxxxxxxxx> [Chrysler300] wrote:


As I understand it, putting a lower pressure cap on the system would increase your chance of boilover, since you are reducing the boiling point of the coolant. I would stay with factory. If the seams of your rad are letting go, I would blame the workmanship.

Ron

________________________________
From: Chrysler300@xxxxxxxxxxxxxxx<mailto:Chrysler300@xxxxxxxxxxxxxxx> [mailto:Chrysler300@xxxxxxxxxxxxxxx] On Behalf Of 'Henry Schleimer' henry.schleimer@xxxxxxxxxxxxxxx<mailto:henry.schleimer@xxxxxxxxxxxxxxx> [Chrysler300]
Sent: Tuesday, October 17, 2017 7:47 PM
To: Chrysler300@xxxxxxxxxxxxxxx<mailto:Chrysler300@xxxxxxxxxxxxxxx>
Subject: [Chrysler300] Radiator cap pressure 300C

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






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