1940-5019 8cyl lasalle? 4lb.rad cap.

[symplesymonsezzz]

Hi. I need to replace my rad cap because it was making a noise. The cap on the car is a 4 lb. also has rc on the cap. Is this cap suitable/original for this car, the engine is a 322 ci. The rad was down about 1 gallon which may have caused the noise, but I will change the cap. Autosource said use a 7lb cap, I think they somtimes say things just to make a sale. Once again I turn to this forum as I have in the past. Many thanks.

[Jim Stamper]

     Important to make sure the replacement is long enough to make a proper seal. Slightly longer necks on these radiators, needing a slightly longer cap. This was gone into very recently here, a quick search here might give you more.  Jim Stamper, CLC#13470

[symplesymonsezzz]

Mr. Stamper, thanks for your input. I did a search and found an article by Bill Ingler feb 1 2015 which he talks about 41 to 48 7lb rc caps and the sealing rubber sticking and caps with long necks. The cap on my 1940 lasalle is a 4 lb. rc and may have been changed. I am asking what poundage cap should be used 4,5,6,7or8lbs. Quick search showed only Bill Inglers message and as he say's I will loosen the cap when storing the car. I have trouble finding things on the computer/internet for me it is not user friendly, more of a challenge. Thanks Jim.

[Bill Ingler #7799]

Jim: The correct cap for that year is a cap made by A/C and is a RC-3 and shown below as a 7 lb cap. You can sometimes find one listed on ebay. If you buy another brand cap, remember that the cap height should always be longer than the depth of the neck of the radiator so when you push down against the cap spring to lock the cap, the cap then will seal against the bottom of the radiator neck.  If you are going to store your car for any length of time, loosen the cap as the rubber seal on the bottom of the cap will sometimes stick to the bottom ridge in the radiator neck and tears the rubber seal when you go to open the radiator cap.    Bill

[symplesymonsezzz]

Mr Ingler, many thanks for your input. I will look into finding a 3lb cap. Thanks again.

[TMoore - NTCLC]

Just to clarify, and RC-3 is NOT a 3 pound cap, but a 7 pound cap.  Putting a 3 pound cap on your system will likely lead to boil-out since it will not keep the pressure high enough to prevent boiling.

[symplesymonsezzz]

Many thanks for making it clear and I will look for a 7Ib cap. I like this site becuase people are willing to share and assist where they can. Thanks to everyone for the help.

[Bill Ingler #7799]

Mr. Rice: Several RC-3 CAPS ON EBAY. Once you can get on ebay, type in A/C Radiator Cap. Then click search and it will give you about 10 pages of A/C caps. I think there were three RC 3-caps posted. $30-40 plus postage is about the range. Here is one of the 3 listed on ebay. The one below is original production and you will see later production caps which are the correct RC-3 caps for your car but produced probably in the 60s with a different top to the cap. These are slightly cheaper if originality is not mandatory on you part.  Good luck    Bill

http://www.ebay.com/itm/1949-1950-1952-Ford-Mercury-NOS-New-AC-RC3-Radiator-Cap-/370874877567?hash=item5659dd867f&vxp=mtr

[symplesymonsezzz]

Mr. Ingler. I did the ebay search 3 pages. Found about 4 that said 7lb caps, but didn't say rc-3. Under compatible vehicles, my year was not listed so I will keep looking. I did the "save search" On ebay and will get email alerts when somthing new comes to the listings.Thanks to you I now know what to look for. Thanks again.

[Steve Passmore]

This is a 7lb RC3 and lists it for all Cadillacs 39 to 40.

http://www.ebay.com/itm/NOS-AC-Radiator-Pressure-Cap-RC-3-850797-100-132-SH-/351542459717?hash=item51d9903d45&vxp=mtr

Heres another.

http://www.ebay.com/itm/1939-40-CADILLAC-RADIATOR-CAP-IN-BOX-NOS-GM-AC-RC3-/331600132905?hash=item4d34e87b29&vxp=mtr

[symplesymonsezzz]

Steve Passmore. Just want to say thanks for the link's. Sorry it's taken so long. Thank's again.