Those built from 1938 onwards, commencing with N°858, had small steam domes, sedan cabs with welded tenders and also larger diameter (9+1⁄2 in or 241 mm) piston valves.

A number of modifications were carried out over their life including the fitting of large mushroom air snifting valves.

Several had additional sandboxes and/or rear headlights fitted at various times for working lines where no turning facilities were available.

[1][3] On 5 May 1947, C17 class locomotive 824 left the rails near Camp Mountain on the Dayboro line claiming the lives of 16 people and 38 injured.

The Commonwealth Department of Trade & Customs Recreation and Social Club had chartered the train for a picnic at Closeburn.