Two passes are better than one, Allstar dual pass radiators get twice the cooling efficiency With these radiators, water is circulated across the top half and then back across the bottom half, allowing twice the heat dissipation. Dual pass radiators offer two rows of 1 in. tubes, furnace-brazed tanks, a machined billet filler neck with overflow, and a standard 1 3/4 in. outlet. for your vehicle with quality-built Allstar dual pass radiators.