Packard Forum Index » Post-War (1946-54)

Tim (TL) entered this post in the Chat Room:

"My Packard is a 1951 300. The 7 lb. radiator cap is fairly new but seems to be slightly leaking so I ordered an AC Delco RC6 which is shown as a replacement upping the pressure to 13 lbs. The dimensions were to be "Product Dimensions 2.5 x 2.4 x 1.5 inches" but the height is just over an inch. Any suggestions for a different one?"

Reproduced here for a wider audience and will advise Tim.

I wouldn't use a higher pressure cap. In fact I wish I could find a lower pressure for my modern car because the system is getting old.

I found a 7 psi cap that fit the Packard radiator at one of the Ford V-8 vendors. I don't have the box anymore so I can't tell you where it came from.

Good Evening Tim...The Packard Radiator Neck is longer than normal. That is most likely why it is dribbling/leaking. You can obtain the correct one from Max or Kantor or perhaps someone will give you the number for the cap at NAPA. I used to have the number, but can't find it tonight. Ernie

Looking in the Packard Parts Cross-Reference here on PackardInfo, seems there are a number of options.

There is controversy surrounding the correct pressure cap for 24th through 54th series (1951-54) radiators due, I believe, to a typo in the 22nd-54th series parts list. Both a 7# and a 13# cap are listed for "all" 24th-54th series cars. That's quite a difference in pressure, could they be used interchangeably? I believe the 7# cap is for 22nd-23rd, the 13# for the 24th-54th.

At time of purchase, my '54 Convertible had a 7# cap with the correct filler neck length. It dribbled coolant out the overflow tube at the drop of a hat, even when the cooling system was nowhere near overheating. If you let that go long enough, the system will overheat due to a low coolant level. Installing a low temp. thermostat and an electric cooling fan made no difference in the dribbling. So I thought I'd try a 13# cap. Had a heard time finding one, finally Max Merritt located a 14# cap so I bought that. The new cap took care of the problem. No more excessive dribbling, no overheating and the coolant stays at the correct level in the radiator. Based on my experience, I recommend that Tim proceeds with the 13# cap and lets us know if that works for him.

I have installed dozens of Napa 703-1411 caps (7psi) over the years with great results.

I think I'll change my opinion then if the cars were being delivered with the higher pressure cap. The radiators on the 24th and later series were smaller so higher pressures might be needed. I never saw an original high pressure cap so maybe Packard was making that dual specification for extreme climates.

As well those motors run hotter with age so I might consider installing an overflow bottle rather than risk blowing a hole in the heater core or radiator. Given there is no expansion tank the correct level of coolant is that which covers the cooling fins. The top tank is the expansion area. Using that level I never had a problem unless there was another issue with the cooling system.

If you want correct radiator caps that match the OEM caps in appearance, then this is a source. They are produced under license from GM (AC). Scroll down for their Packard application chart.

oldcarstuff.com/radcap.html

There may be a couple of misprints -- or changes with the cap pressure.. Originally 51 - 52 were 7 psi but in SC Vol27#2 they introduced a 12 psi pressure cap for the 26th series senior models. Said it was also available as a service part for 24 and 25 series cars and they didn't appear to restrict it to any particular models. The specs for 53 seniors and all 54 except 1 chassis says 12psi. Parts book doesn't mention that 12psi cap but has another part # listed as a 13 psi for all 51-4.

I replaced a 13 lbs radiator cap with a 7 lbs. cap on my 55 V-8 Clipper and never had any problems with it venting or the system running hot. Radiator had been service and I replaced the stock 4-blade fan with an after market 6-blade flex fan.

(o[]o)