Coolant Overflow Bottle Question

New to site so you can understand if this question is too dumb.

I have a 1974 Dart Sport 318. Radiator was previously changed out from 19" to 22". Coolant overflow hoses were removed.

I know the molded in tube from the bottom of the bottle connects to the radiator and one of the fittings on the green cap is for the overflow, but what is the other cap fitting for? (One small and one larger)

As they say, any help would be greatly appreciated! :cheers:

Thanks, Another Mike
Author: admin