Abstract: A thermally insulating fuel filter cover provides thermal insulation of the fuel filter of a diesel engine such as is used in the trucking industry. The cover is a flexible cylindrical body of thermal insulating material such as expandable urethane foam which has a closed end, an open end, and a hollow interior portion for receiving the fuel filter. The cover is slidable over the fuel filter and is flexible so as to form a friction fit. The cover encloses the exposed surfaces of the fuel filter and provides thermal insulation to help prevent waxing and freeze-up of the fuel in the fuel filter in cold weather.