No it doesnt cool the engine your right. But if its stopped up its limited the flow of coolant and slowing the flow down in other words coolant is going in but not coming out. Therefore it's not pumping thru the block as efficiently. By bypassing it your removing the amount of area the coolant flows. Your absolutely correct you dont need it that's why I said bypass it. It may not be the problem but it is a free test that couldnt hurt to try.
