Radiator cap pressure

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By DryLakesRacer - 2 Months Ago
For the last 9 years I’ve been using a 7 psi cap and leaving the coolant down an 1” in the tank.
This week I built a coolant recovery system that can hold about 22 oz of coolant when full so I can fill the radiator full to the top.

My question is: should I change my radiator cap to 14 or ever higher.
By Tedster - 2 Months Ago
Is the radiator itself of modern construction or materials designed to support those higher pressures? That's the question.

I have a modern radiator in my truck but - I also wonder about the near 60 year old heater core, which are made of unobtanium and/or a pita to replace.. I've ran a 7 lb cap and a 195° T-stat for years with no overheating or vapor lock or anything like that. It doesn't get quite as hot here as Southern Cal, but we're definitely no slouch in that department
By 57RancheroJim - 2 Months Ago
Why would you want to change to a 14# cap? I've run all three of my old cars with 7# caps in SoCal 100 degree temps for years with no issues.
By DryLakesRacer - 2 Months Ago
Jim, it’s because of modernization of all the components and the possibility that the 20oz or so would not be enough. Right after I purchased our 56 I filled the radiator and of course it pucked out some coolant. I remembered why and have been running low in the tank for the last 9 years. Living within 5 miles of the ocean I rarely real hot days. I just wondered what others did with their cars of this era as they modernize.
By Town Vicky - 2 Months Ago
I have run overflow system for 40 years and no problem original rad. I did get a 7lbs overflow cap they make them.
By DANIEL TINDER - 2 Months Ago
If you changed to a much higher temp. thermostat (to increase efficiency), a higher cap pressure might be needed to raise the coolant boiling point.  The advantage of a recovery tank is avoiding the deterioration of traditional antifreeze & the system corrosion caused by exposure to air, plus the need to constantly top off the coolant water component  that evaporates. If nothing else has changed, and ‘boil-over’ was never a problem previously, the additional coolant volume that is now possible should make a higher pressure (and the danger of resultant component failure/leaks) even less necessary (?).
By 57RancheroJim - 2 Months Ago
I always left the coolant an inch or so low in the radiator for expansion back in the old days. After installing recovery tanks I found that wasn't needed. After a run if there is any expansion in ends up in the recovery tank. Mine tank usually goes up 1-2" and as the car cools down that amount is sucked back into the radiator. I seldom remove the radiator cap but when I have it's full to the top.

By DryLakesRacer - 2 Months Ago
Thanks for all the responses; probably overthinking how much coolant will be coming into the over flow. The photo shows the aluminum water bottles I received from AAA a gift I guess which I decided to make the tank. The radiator is full and I have put 2” of coolant in the tank. There is a breather in the cap. If it lets some out showing it’s not big enough I’ll make another or try the 14 psi cap.. thanks everyone.
By 57RancheroJim - 2 Months Ago
That looks good. AAA never sent me one or anything else. I just have the cheap auto parts store plastic ones, I like your better..
By Tedster - 2 Months Ago
DANIEL TINDER (2/16/2021)
If you changed to a much higher temp. thermostat (to increase efficiency), a higher cap pressure might be needed to raise the coolant boiling point.  Wink.

Why would that be? It sort of begs the question - the shop manual says thermostat in '64 startS to open at 185 to 192 F and fully open at 210 F. It looks to me this wasn't for reasons of efficiency or emissions but but the desire by Ford for longer oil change intervals, less sludge and condensation. This was about the time of the new Rotunda filter and the 5,000 mile oil change?