If you’re doing an LS swap, chances are you won’t be running a heater core in the platform you’re swapping. Whether you’re doing an LS swap or building your LS-powered racecar, the Mishimoto Silicone GM LS V8 Heater Core Bypass Hose is the easiest and cleanest solution for bypassing your heater co re. Our bypass hose is constructed from heat and pressure resistant 5-layer silicone and tapers from 3/4" to 5/8" to fit the “in" and “out" ports on your water pump. Bypassing the heater core with a bypass hose is the preferred method, as opposed to blocking off the ports. This allows coolant to flow for your thermostat to function properly and avoid overheating. As with all our products, the Mishimoto Silicone GM LS V8 Heater Core Bypass Hose is backed by our signature Mishimoto Lifetime Warranty.