Diesel 911 is a winter emergency use product. This Winter Rescue Formula reliquefies gelled fuel and de-ices frozen fuel-filters to restore the flow of diesel fuel to an engine. Diesel 911 does not prevent fuel gelling – use Diesel Fuel Supplement +Cetane Boost (in the white bottle) as a preventive measure to keep fuel from gelling. Diesel 911 and Diesel Fuel Supplement +Cetane Boost are compatible in diesel fuel and may be used at the same time.