centralcalvette

So I finally have my 69 427 running. I had the original radiator rodded out as I damaged the filler neck trying to remove the radiator cap. The filler neck was too close to the support and pushed on the neck and damaged it.
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I had a few reproduction radiator caps and the radiatr would just leak from the cap area. I checked the cap and it released much to low at 6 psi. I got a pair of caps at Oreillys by application and they were 13#. The radiator leaked like mad. I got some 16# caps this morning and after reading up on it, set the coolant level 2-3 inches below the radiator cap.

It still leaks, but now it's just a drip, not a gush. When I turn it off, it leaks more and the expansion tank cap blew out the overflow.

Any ideas? The caps don't really seem to have much resistance when going on, as if maybe they're too short. I can't get mu pressure tester on the expansion tank with out a struggle. I don't dare put it on the radiator as I don't want to damage it again.

Using my infrared thermometer I'm reading 195 at the thermostat for about 30 minutes of idling, then it crept up to 204. The upper hose was 160 lower 130. I'm thinking that maybe the radiator neck is still buggered up.

67:72

Sounds like it's not the caps but the "keyed" rolled under section of the filler neck that is compromised. If the rolled under portion has been squished (effectively shortened), it doesn't give the cap the sealing purchase against the inside surface of the neck. When a cap is installed on the neck, does it have any up and down movement? (It shouldn't.)

MelWff

You are not supposed to have two pressure caps.
Exactly what kind of expansion tank do you have, a picture would be best?

centralcalvette

I can't download the picture, but it's the aluminum expansion tank on the passenger side fender area.

doorgunner

I tthink he has the factory expansion tank and ALSO has a radiator of some sort with a neck for a radiator cap.

CENTRALCALVETTE...... lay a sheet of 100 grit sandpaper on a flat piece of metal that is larger than the neck of the radiator where the cap fits.
Then sand the top of the neck where the cap seals until the sealing area is shiny all around.
The put the13 lb. cap on the radiator and fill the aluminum tank halfway full.
Start the engine and let it idle...watch the temperature gauge as the engine warms up.
Let us know if the RADIATOR CAP leaks.

MelWff

If you actually do have two caps the cap on the radiator has to be turned into a dummy cap. First you need a 1973 cap which has a complete rubber seal under the cap otherwise it will leak. You then have to remove the spring loaded center assembly to make it a non- pressure cap. The cap on the expansion tank has to be a RC26 15 lbs cap.

centralcalvette

Ok, So according to the Stant catalog, the 73 and 69 use the same cap, I have an RC26 and I have two 13 and 16 # caps. I'm thinking about using the RC26 as the shaft that holds the spring shaft is tight and may not leak. On the others I have the spring shaft is loose and it seals down in the "well" so there's no pressure at the top sealing surface. So I'll try it tomorrow and see what happens, wish me luck.

If anyone knows what part number or application a cap with a pressure release is I'd like to know.

MelWff

They do NOT use the same cap.
69 uses RC15
73 uses RC33
RC26 is for the tank.
You can NOT use two pressure caps on the cooling system if you have a tank.

centralcalvette

I agree that two pressure relief caps probably won't work. The RC33 crosses to the regular 16 pound cap that I tired. I found a no relief cap for an old Saab and have it on order. In the mean time I'll try to make one of my caps work. I don't think they'll hold pressure without the spring mounted gasket though.

MelWff

The reason they use an R33 is to prevent galvanic corrosion nothing to do with pressure. Jaquar also has a blank cap which I use on my radiator with the RC33 on the tank. Stant isn't going to make the correct cap.

67:72

This still hasn't been clearly answered: Do you have a radiator filler neck with cap and the aluminum expansion tank with cap?

As has been mentioned, you shouldn't have both. The radiators used with the fender expansion tank did not have a filler neck and the radiators with a filler neck did not use an expansion tank. If your radiator has the neck, then I'd disconnect the line to the expansion tank and just run it as a simple overflow to the ground with the pressure cap there. (Proper fill level would be about 2-3" below the neck.) If you really want to keep the tank, then think about replacing the radiator with the correct one.