The original OEM B58 heat exchanger is a 1-row unit that is 27mm thick. In comparison, CSF has used its industry-exclusive world's largest 2-row core (68mm) with CSF's B-Tube technology. A unique tank design allows the larger CSF core to still fit into the OEM cooling system housing. Another critical feature of the CSF BMW B58 high-performance heat exchanger is its unique triple-pass flow design. The water traveling through the upgraded heat exchanger flows through the radiator three times before exiting the cooler and flowing back into the manifold charge cooler. This ensures that the outlet water temperature of the heat exchanger is the absolute lowest it can be. The OEM design, as well as more expensive aftermarket designs, all have single-pass flow structures.