Arnold Rimmer once took two skutters and went on a ramble through the Diesel Decks as part of a 'vacation'. The Diesel Decks were so so large, and filled with so much machinery, that Rimmer's hike took ten days, with Rimmer and the skutters sleeping under the machinery. Although, this also may have been because the anally-retentive Rimmer stopped off to take photographs of every cistern, pipe, gear and valve he came across, noting their manufacturer and model numbers.
After his hike in the Diesel Decks, Rimmer planned to show his slides of the vacation to Dave Lister, who was recovering from space mumps in the Science Room at the time. Rimmer took over a day to load his slides into a projector in the sleeping quarters, and when Kryten told Lister about it, Lister feared it might finish him off.
As the gang traveled to Justice World, Kryten was forced to endure Rimmer's slides in the ops room of Starbug, and was so bored by the banality of it, his intelligence circuits melted. ("Justice", Series IV)
The Diesel Decks are also mentioned in Series X. When Lister said that he was missing the human race and feeling depressed, Rimmer suggested that Lister 'manned up' and go for a 'bracing' walk in the Diesel Decks. Lister was not too responsive to the suggestion. ("Dear Dave", Series X)
The Diesel Decks are seen for the first time (other than in a photo) in the final episode of Series XI. The Diesel Decks appear similar to the cargo bays, albeit with pipes and valves everywhere. There are also gigantic tanks of hydrogen.
After the Cat was seduced by Ankita - a female polymorph in the disguise of a female Felis sapiens - Cat found himself pregnant with eight morphlings. After giving birth to them, the crew planned on flushing them out of an airlock, but parental instinct took over and Cat fled into hiding with the morphlings. Rimmer came up with a plan to narrow down the search, which included turning off all heat inside Red Dwarf except in the Diesel Decks, which would force Cat and the morphlings to go there. The plan initially worked, although it resulted in three Listers, three Krytens, and three Rimmers all pointing guns at each other in the Diesel Decks. The situation was resolved when Cat blasted the morphlings, leaving the real Lister, Kryten and Rimmer safe, albeit covered in green goo. ("Can of Worms", Series XI)
When Kryten manipulated Rimmer into mopping B Deck, Rimmer only realised when Lister pointed it out, explaining that the manipulation was part of Kryten's development course. Angered by this, Rimmer handed the mop to Kryten, and ordered him to mop the Diesel Decks instead - all five miles of them.
Kryten became so absorbed in mopping the Diesel Decks that he barely noticed a flashing yellow alert. When he eventually did not notice it, he ran back up to the Science Room on G Deck to help the others. ("Mechocracy", Series XII)
- Since Red Dwarf was powered by the Front Ramscoop directing hydrogen from space into the main engines (a fusion reactor), the Diesel Decks were certainly not part of the main engines of the ship. It is unclear exactly what purpose the Diesel Decks served, since fossil fuels such as diesel had long since been made obsolete by the time Red Dwarf left Earth. The ship also has solar panels and battery back-ups. It is possible that diesel is still used as grease and lubricant, if not fuel, and thusly the area gained it's name from the smell.
- It is possible the Diesel Decks provide power for other areas of the ship except propulsion, or for mining activities, since Red Dwarf is a mining ship owned by the JMC, and has two small moons embedded in it's underbelly for the purposes of mining.