This is a 4 part song. Only the 4th part has a melody.
This song represents the old steam merry-go-round, which, after the engine started, gradually built up speed and noise until the tinny melody was heard above the tud, steam and squeaks of the engine. Music over, the engine slowed down, noise dying away until it stopped completely. Strong leadership is required to bring in the four parts, and increase and decrease the speed. The leader beats 3/4 time, slowly for part one but gradually increasing tempo as each additional part enters.
Part 1: oom-pah-pah. [Engine warms up] Four times on own, but continues throughout.
Part 2: oom-sss-sss. [Steam building up] Four times, then add:
Part 3: oom-twiddly-dee-dee. [Very high squeak] Four times, then add:
Part 4: the melody starts as full speed is reached. This part of the group sings da-da-da with suitable "tinny" sound (eg. hold noses!)
When the music is finished, the merry-go-round slows down, gradually losing its squeak (part 3), then the steam (part 2) until the engine (part 1) finally stops.
Source: Jubilee Songbook published by Girl Guides of Canada.
Original source unknown. Probably public domain. May be reproduced.