coolant recovery radiator caps: THEORY?

[chevyconvert]

I got tired of waiting for my '70 radiator overflow to stop piddling ever time I pulled her in the garage after a drive (never did).
As discussed in an earlier thread I decided to swap out my original electric windshield washer reservoir
with a reproduction manual washer reservoir and use it for coolant recovery.
Routed a new 6' 3-ribbed hose from the overflow, down under the radiator and into the bottom of the new reservoir. Just finished up today and have not started her up yet but the install is slick if it works.

My question is about the radiator cap. I bought a new one from THEMOPARSHOP.com that's supposed to be correct for fluid recovery :(AMK-ARC-70SM) 1970-1974 CHRYSLER CAP.

The only difference I can see between this new cap and the old cap that was on my car is it lacks the larger upper rubber gasket. Won't it leak at the neck without it?

How do these caps work differently to suck the coolant back into the radiator?

[Chryco Psycho]

it should have the larger gasket for th eneck , the newer caps have a spring loaded center plug in the middle of the smaller seal for the inner neck this will pull down as the fluid contracts allowing coolant back into the rad

[chevyconvert]

well I tried to find the camera...couldn't 

So it doesn't sound like this one is right. I can't see how it can seal with no large top gasket and just a thin brass plate.

Without that gasket it couldn't build a suction to pull the fluid back in..right?

edit; wife found camera...one on the left is the new recovery one...can that work with just a metal disc?
the one on the right is my old one

[Chryco Psycho]

I would use the old one , it seems to have the rocovery plug in it

[chevyconvert]

 

Went for a drive yesterday, pulled her in the garage and coolant was in the reservoir.
came home from work today and it was gone, sucked back into the radiator with the old cap.
Small victories are still victories !

So I guess i should have a small amount of coolant in the reservoir when cold to keep air out right?

Thanks again CP 

[Chryco Psycho]

I would put a small amout of coolant in the overflow to eliminate any air in the system