I'm not sure I understand your question.

I don't know how the actual plumbing inside them is routed, maybe the air in the unused part acts as an insulator?

The 2-cooler one I switched out was almost new, put in by the PO.

The car used to hover around the second line unless it was moving, when it would hover around the first. Now, it hovers around the first line all the time. It actually gets hotter a bit as the speed increases.

 

The coolers are just a flat plate thing.kind of sitting in the end tank, with nothing going through them I really can not see how it could degrade the cooling much at all.
But it seems to have worked for you, so who knows.

 

Yeah, dunno. I changed out the thermo stitch at the same time, but that wouldn't have made any difference. Maybe the old one didn't have that flow baffle thing? Assuming my present one does.

 

I can also offer $50-$100 for your core.
$50 for no cooler
$75 1 cooler
$100 2 cooler