66.............a double and or triple pass radiator has dividers inside the radiator. The coolant goes thru the top half of the rad then it drops down and flows over the spacer to a hole where it starts again the flow. The problem is the time it takes. I guess I didn't quite explain it as well as I should.
It all comes down to flow and you want the flow not interrupted in a cooling system. A double or triple pass has interruptions in them.
Double and triple pass radiators work well in an all out race car. And yes, I have seen and talked to some guys who do run them on the street. But I have always heard them complain on how much hotter there motor runs as well.