Over time, the factory heater core tubes on your 1st and 2nd generation 5.9L Cummins can become corroded and start leaking. Coolant leaks can create engine overheating issues, ultimately leading to engine failure. Stop these leaks in their tracks with the Fleece Performance Heater Core Line Kit. This kit is constructed with upgraded stainless-steel tubes and a high-temperature silicon hose. This kit contains everything you need to replace your heater lines from the block to the firewall and is designed as a direct replacement for all trucks originally equipped with air conditioning.