The Lionel 6-18018 is a 2-8-2 Southern Mikado locomotive. I would consider replacing the traction tires. I believe the 242-206 woudl work fine and is available from most parts suppliers, including form sponsors @S AND W and @Harry Henning respectively:
http://www.sandwparts.com/Parts%20List/6-XXXX-XXX.pdf
https://hennings-trains.shopli...ires-for-lionel.html
Getting a little more involved would be to take a gander at the service manual for the locomotive and tender:
https://www.lionelsupport.com/...231-8018Complete.pdf
https://www.lionelsupport.com/...8018-T01Complete.pdf