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Coolant System Tanks and the Proper Caps?

Hi Gang,

One of the many items I'm inspecting this winter is the cooling system on my car.  I already found a non-stock thermostat and restrictor plate, and the caps on the system tanks may be another possible deviation from stock...

But first and foremost, how can I tell if the filler necks on my tanks are US spec or European spec?  There must be a measurement I can make, no?

Meanwhile, here's a photo of my leaky main tank:


It has a older Stant 13 PSI cap on it now, it's obviously not sealing well.  Before I try a new 16 PSI cap, I'd like to be sure I've got the US filler neck installed.  I do believe these are aftermarket tanks in my car, as they are not in the OEM locations, and the main tank does not have a temperature sending unit bung.

Regardless of the pressure rating I end up choosing, should the cap on the smaller tank be 'vented', or 'non-vented'?

Looking at the larger tank in the background, I noticed that it also has a pressure rated cap.  It's got a 14 PSI lever vent cap installed now, but from what I've read, this should be a non-pressure rated cap from NAPA or equivalent.  That will allow the large tank to function as a recovery tank, correct?


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