Several sources show either ¾" or 1" deep caps (Mike's Radiator, View Products 541- 660- 7618). 1" still isn't deep enough based upon your measurements. So here is the part that Dennis Carpenter recommends Radiator Cap Original | Dennis Carpenter Ford Restoration Parts. You might call them and ask how deep it is.

 

I don't think there's a problem with the NAPA cap. The spring of the cap gets compressed a small amount when installed. On a 4 psi cap, there won't be much compression. If pressure goes above 4 psi, it will lift the rubber by compressing the spring further, and blow out the overflow tube. I'd guess on mine the spring is compressed no more than 1/4" when installed. The spring is never completely compressed.

No part # 8067 listed, I can only guess it is a "stilling tube", it would seat on the bottom of the neck and the cap would seat against it. Gives you a datum for initial fill, but I've never seen one on any of our trucks.

 

I agree with Ross on 8067.

The problem with the cap that Wayne has is that it is not seating against the bottom of the radiator neck so the radiator through the overflow is open to the atmosphere so it cannot build up pressure. Am I right Wayne?

But, IMHO this still does not explain why he is "burping" out so much fluid. I still think something is locking air in there.

 

As I understood his measurements, the neck is 1.09" deep, and his cap is at least 1.4" tall uncompressed.

 

Yes but then in post #27 he says that the new cap is only .844" deep which leaves him short. I agree with you that the old cap should work (see post #25). I still don't think that his radiator cap is the problem rather air trapped in the system.

 

I agree, Pete.

I used to own a car that was notorioous for air-locking at the heater. The trick recommended there was to drill a 1/8" hole on top of the upper heater connection, near the end of the stub. When filling you would pull the hose almost all the way off, exposing the hole, to let air escape. Once water started coming out of the hole, slide the hose over it and clamp.

 

No the cap is 1 1/4" from the TOP of the cap. That's just how they show it in the pic and that's what mine measures with a caliper. But, from the underside of the cap where it seats on the top of the radiator neck to the bottom of the rubber gasket that is supposed to seal is just under .9". Called Dennis Carpenter and talked at length with them. He grabbed the cap for my truck which Pete linked above and that cap measured 5/8" from the underside to sealing surface. What he and I both think is this.....when I put the cap on it should be like all caps I've ever put on. You press the cap down with your hand just a little bit and turn it. This would be like Ross said....his only compresses 1/4". Problem is mine doesn't compress at all. The spring (or bottom of cap to radiator) never compresses before turning so its not touching the lip on the inside of the radiator neck. He suggested I make a small rubber washer kinda like in a garden hose to take up the slack. This might would work but seems silly to be doing this. I ordered the correct cap and referenced multiple caps online and on the phone and none measure right.

 

Heck I don't know. Me and Vince from DC agreed that with the cap not sealing enough when you put it on and the slightest bit of pressure increases it will instantly start running out the overflow....which is exactly what is happening. I have to get this figured out. Seems like a different cap is out of the question since none measure longer than the one i have.

 

Go to a radiator shop, they will recognize the filler neck and know which series of caps works. But it could be there is no 4 psi cap with the correct dimensions.

Or they can sweat on the correct neck, very quickly and easily.

 

That would work well!

 

It only take 4 lbs to overcome the pressure. The real question is why is it expanding cap or no cap. Liquid does not expand but air does so you must have air in there. Assuming that you have a heater Ross's trick is worth a try. But I would put the gallon jug on the overflow first (put the tube all the way to the bottom) to see if cycling cold to hot and back again reduces the amount of fluid burped out each time which means the air is working itself out of the system naturally. If the tube is in the bottom of the jug as the engine cools it should suck the fluid back into the cooling system.

 

Just got off the phone with Stant's engineering dept. They are emailing me a group of tables that will allow me to see if a different neck has been put on at some point. They told me to measure the radiator and call them back...very nice folks. Also told me that the brass part I was measuring to didn't in fact touch the neck. On a flathead radiator I needed to measure to the very underside of the cap. So that throws my measurements off some. Waiting on tables now.

 

Here's what I got from Stant. It's a pdf file. I put it on my website so y'all can download or view it if you want.

http://www.waynewaldrep.com/picturehosting/SAEJ164.pdf

Just for reference I've converted dimension "J" and "L" to inches.
J= .215-.225
L= .514-.524

I have to stop back by NAPA and borrow calipers but I can tell you if my "L" number is actually around .8-.9 then...ummmmm. I'll double check the measurement and get back. Thanks for all the discussion you guys!!

 

My "L" came out to .827"....needless to say after lots of measuring and info my cap isn't even close to sealing.

 

I still think you might want to get one of those radiator pressure tester tools.
hook the thing up and see if pressure builds when starting the engine.
You said as soon as you put the cap on, it starts flowing out the overflow tube.
Where is this pressure coming from when it's cold? Even if your cap was defective or the wrong cap, it is creating pressure immediately and pushing fluid out the overflow tube. Classic case of head gasket leak...
Anybody???