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Can you Guys help me with a question i was asked, on a 1939, 8 cyl packard 120 four door.
what radiator cap should i buy? is the system on a 1939 packard pressurised or not? do i buy the cap with 7 lbs pressure or the flat cap type which fits on unpressurised system - any info on this, i need help, Bill

Bill,

System is unpressurised. We recently replaced the cap on a '39 120, see this post. I can mail you a NORS cap if you'd like? Just PM me your address.

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Bill, I believe the 39s use a pressurized coolant system. The '35-'37s used an un-pressurized cooling system. The change to a pressurized system started with the '38. All the previous refers to the Junior cars, like yours. I believe it is low pressure and uses a 3-5 lbs cap. 7 lbs cap is too high a rating. Easy enough to check. Is there a sealing surface below the top surface in the radiator filler neck? If so, it is a pressurized system. Measure this distance to get the correct cap. It is easy to get too shallow of a pressure cap and therefore end up with a non-pressurized situation. To verify, check the manuals section on this site.

(o{}o)

Quote:John,

Is that right? I was under the impression that pressurised systems started in '41. But then again, I've been wrong before!

I was under the impression the pressurized radiator caps came the year they introduced optional A/C. The parts book lists 5 different caps between 1935 and 1941, though it doesn't specify which are pressure caps, though we know 1941 models carried a pressure cap, whether with A/C or not. They were 7 psi as I recall.

I did qualify my posting, but there is a '38 Eight here in Austin (stock as far as I know) with a pressure cap. My '37 115C is unpressurized. Don't believe everything you read on parts lists and manuals. I have a Motors manual that says 1955 Packards were negative ground. I'll still stick to my story.

(o{}o)

FWIW, Max Merritt sells their radiator cap for 1935-1939, 110, 120 models as no pressure (showing equivalent Packard part no. 300593).

I did find this from the Packard Technical Service Data Manual dated 1940,
"Pressure caps are fitted to the super-8's and weather conditioned one-tens and one-twenties. These cars have special radiators to operate under pressure. The radiators on our other cars are not intended to operate under pressure. Do not attempt to fit pressure caps to cars not originally so equipped."

See also the article titled "Pressure Radiator Caps", in SL Vol. 14, No.14, which I found whilst transcribing topics for a forthcoming installment to the site's Service Index. This may be where the 'Packard Technical Service Data Manual' got its info.

Only other reference I could recall was in an article titled 'Alcohol as an Anti-Freeze', in SL Vol. 17, No. 22, advising that 19th-20th Series cars have sealed cooling systems and a pressure cap.

Though I've worked my way through these newsletters back to 1936, our coverage is not complete for 1937, and we've nothing for 1935.

"Believe nothing of what you hear because of lies and nothing of what you read because of errors" Stupidicus 433 BC