The top heater hose in your 6.7L Cummins has a quick disconnect fitting at the engine that is prone to leaking. This leak can not only cause a mess in your engine bay and garage floor but also lead to engine overheating and more serious engine issues. Mishimoto has the fix for this issue. The Mishimoto Top Heater Hose Upgrade. This upgrade eliminates the o-ring seal and reaplaces it with a -10AN connection for improved reliability and a leak free seal. Thread sealant is pre-installed on the threaded adapter for a quick and simple installation.