Diesel Fuel Supplement +Cetane Boost is a winterizer /anti-gel that is used in the cold winter months to prevent fuel gelling and keep fuel-filters from plugging with ice and wax. When temperatures drop, paraffin (wax) in ULSD fuel will gel stopping fuel from flowing through the engine and water in the fuel can freeze on the facings of fuel-filters, blocking fuel flow. Diesel Fuel Supplement +Cetane Boost is intended for use only during cold winter months when temperatures drop below +30F.