The "Märklin Engine" was an off-the-shelf gauge 1 model used to haul rolling stock in the background of the first series for creating the illusion of business. It is a German Federal Railways 80 class 0-6-0 tank engine first produced by the German model railway maker Märklin in 1971.
The Märklin Engine was first acknowledged in the crew member's dedication page on the Sodor Island Fansite. The page featured a behind the scenes photograph of the Märklin engine from the episode Tenders and Turntables. It then appeared on screen in The Flying Kipper in the background shunting and preparing the Flying Kipper for Henry to take away. The Märklin engine also appeared in Off the Rails and was used as one of the tarped workshop engines in Trouble in the Shed. It can also be seen in a still from Thomas' Train pulling a small goods train next to Henry at Knapford.
When the second series started production, the Märklin engine was no longer needed and other engines were used to haul rolling stock in the background. Because of this, the model was cut up and used as set dressing. A scrap smokebox of the Märklin engine later appeared at Crocks Scrap Yard in Edward, Trevor and the Really Useful Party, the numbering and lettering was still visible on the model's smokebox door. A Märklin BR 80 chassis was later used to push trucks along and is seen in Put Upon Percy and Busy Going Backwards.
A scrap model of the Märklin engine was later included in Blue Mountain Mystery in a scene at Vicarstown Dieselworks by Greg Tiernan as a nod to the scrap engines seen in the background of series past.