D199, nicknamed "Old Reliable" and "Spamcan", is a rude Diesel engine.

He visited Sodor on a trial with D7101 (later known as "Bear", see below), and talked about taking over the railway. He and Bear argued, and the other engines took an instant dislike to D199. One afternoon Henry the Green Engine found D199 moaning near a signal box because he had engine trouble, and the signalman called him "Spamcan". Henry rescued both the engine and his train, and D199 was soon sent away in disgrace by the Fat Controller.

Although he does not appear in the television series, D199 appears in the magazine story Diesel Day! published on 16 May 2001.

D199 is a 1Co-Co1 diesel locomotive based on the British Rail Class 46. The number D199 is fictional but would be correct for a Class 46 if another six had been built: they were numbered from D138 through to D193.