Sidney, nicknamed Sid, is a bit of a forgetful Diesel engine. He starts his day at one location and ends up at another, not remembering how he got there. When it was his turn for repairs at the Dieselworks, he was hoisted up and had his undercarriage removed. Being patient, Sidney was happy to wait... and wait... and wait. He sat there happy to pass the time with any engine that happened to be visiting. Percy helped him get a new set of wheels and now he is back on track.
- Sidney is best friends with Lightning Dust.