bdchase73

Hey All:

Heading out to get some parts in a few. Hope someone can answer this before I head out.

Have a Dewitt Radiator and they say any 15pd stock cap will work on it... But, does anyone know if that same cap will fit the expansion tank on a 69 vette?

MelWff

Why would you put two pressurized caps on your system? If you use the pressurized expansion tank you need a dummy cap on the radiator with a sealing ring for the neck.

pws69

..... but YES, it WILL work that way!

bdchase73

Both are under pressure in the 69. The expansion tank runs a line from the pump to the heater core. If that was not pressurized would have issues. Also just got back from the store. Picked up two rad caps and it did fit on the tank.

MelWff

Someone changed something on your car. If the car originally had an expansion tank it would have a radiator with a tube on it and no neck and cap. In addition if you check what was originally used, the expansion tank used a special cap to protect the aluminum from electrolysis.

http://www.ecklerscorvette.com/corve...late-1972.html

Mike Ward

Bubba has visited your car. No Corvette was delivered with two radiator caps. You either have the wrong rad in your car or Bubba added an expansion tank.

rponfick

Yes, and Dewitt's has the correct one in their Perfect Fit series. I just got mine for my '69, and it has the little spout that goes over to the fender mounted expansion tank. Also can be gotten in manual or auto tranny fittings. It sure is purdy.

Ralph

Easy Mike

Yep. If the stock radiator had a cap (copper/brass), the car did not have a surge tank. If the original radiator had no cap (aluminum), the surge tank was required.

bdchase73

Thanks guys... Still a little confused. The car was the 350 350 and had the original rad in it when I got it. I replaced it with a Dewitts. It is basically a BB rad made for the 350 and the housing so it bolts right up. You are correct as well that the car did not have the expansion tank on it when I got it. I added it. Did I screw up by doing this? Also, is it ok just to run the two caps? They were so cheap I got two and put one on the rad and the tank. Both fit just fine.

BTW I am Bubba as I added the tank

noonie

You can use the expansion tank as a overflow or recovery or surge tank. Commonly called a few different names.

Don't know exactly which style expansion tank you have and with how many ports, but the idea is to be able to suck fluid back and not air into the radiator when it cools, so it's easiest to use the bottom port for that. The top port(s) should be left open if the 2nd cap will be tightened.
Otherwise just get a recovery tank.

74modified

You could set it up as a pressurized surge/de-aeration tank as used on late model cars. I have one set up on my LS swap - but it is a Mercedes tank. It is the highest point in the system and continually removes air from the system = better efficiency. Using a higher rated pressure cap on the rad insures that the surge tank will be where any "burping" happens.

noonie

You have the reversed, lower pressure on the rad and preferably whats know as a "blanking cap".
The remote tank becomes a pressurized expansion tank only, but it will require a pressure rated feed hose setup.
Some British and Australian cars were set up this way with the old style bayonet neck rather than the newer screw on plastic.

74modified

Yes it is all pressurized, except for the overflow off of the pressure tank/bottle. I do have the higher rated cap on the rad and as such it is just a plug. If you look, most all new cars are plumbed this way. As the high point of the system, and in the circulation loop, air/steam is taken out continuously.

Mike Ward

You did no harm- it just provides little or no benefit. If you want to be Dubba Bubba, add a coolant recovery tank to catch any possible overflow from the expansion tank.

Easy Mike

Does your replacement DeWitt's radiator have it's own fill cap? If so, the expansion tank should not be needed.

bdchase73

No the rad came with no cap. He said to just get a 15pd cap and call it a day. But then he did not know about the 2nd tank. Will take a few picts and put them up tonight. Thanks for all the responses.

MelWff

I have the same set up. You need a cap on the radiator without the center spring and attachment but with a rubber gasket ring so it seals against the neck, a RC-10 may work if you add the rubber ring. I found one ages ago made by AC for Jaguar but have no idea what the specifics were. The expansion tank takes the standard design cap but should be this number.

http://www.ecklerscorvette.com/corve...late-1972.html

rep69

My 1969 has the 427 with A/C. The long tube style harrison tank currently has aslant cap. I would like to repalce it with an original cap. Would the cap mentioned in the other posts from Ecklers work?

noonie

I'm glad someone understnds this.

They are properly called a "blanking cap" and a lot of mostly British cars used them including Jag, MG, Morris etc.
Available from British parts houses.
Tridon makes them in all available bayonet sizes.
Here is a pic.

MelWff

Thats it! Never knew the technical term, thanks.