A fuel system includes a fuel passage for conveying a hydrocarbon fuel. The hydrocarbon fuel is reactive with oxygen to form carbonaceous deposit. A device is disposed in the fuel passage such as to be exposed to the hydrocarbon fuel. The device includes first and second surfaces that are spaced from each other by a clearance gap into which the hydrocarbon fuel can infiltrate. The first and second surfaces are in sliding motion with respect to each other when the device is in operation. A frangible fluoropolymer coating is disposed on at least one of the first or second surfaces along the clearance gap. The coating is subject to the carbonaceous deposit adhering thereon. The coating is configured to allow portions to release by shearing off with the carbonaceous deposit under stress from the sliding motion to uncover a newly exposed face of the coating.