
Guinness 3BG is a 0-4-0ST and was built by Hudswell Clarke & Co., Leeds, in 1919. The locomotive was used for shunting Ireland's largest privately owned broad gauge industrial system. The famous Dublin brewery operated an extensive 1'10" gauge system within the complex from 1874 to 1965 with broad gauge locos being used to transfer traffic from there to Kingsbridge (now Heuston) Station for onward transshipment.
When the Railway Preservation Society of Ireland formed in 1965, this locomotive became the first preserved locomotive in their collection. Originally the engine carried side sheets covering the motion, but these were removed by the RPSI for maintenance reasons.
No. 3BG spent a number of years at the RPSI's Whitehead Railway Museum as base of operations before being leased to the Downpatrick & Ardglass Railway for the commencement of their steam operations in 1989. The locomotive was used at Downpatrick between then and 1996, when she was stopped for overhaul. She was returned to Whitehead in 2001 and she soon entered the works for overhaul to running order.
The Guinness engine, when in working order, is primarily used for shunting and the training of new crew members. The locomotive's 90th birthday was celebrated with a cake at one of the "Summer Steam" events in August 2009.

In 2016 the locomotive was steam tested and found to work very well. In 2019 the locomotive reached the ripe old age of 100.