In the Seventies, the question came up on the DR of how to operate more rationally on the narrow gauge lines in the Harz region. The originally planned replacement of the steam locomotives by new diesel locomotives failed for one thing because there were no suitable diesel locomotives in the East Block, for the other thing because foreign currency was lacking to import from the West. Steam operation was thus kept out of necessity. However, in order to reach a certain modernization of the locomotive roster, the decision was made to convert the class 99.23-24 steam locomotives to oil firing. In 1976, road number 99 244 was converted as the first unit. The coalbunker was replaced by an oil bunker with a capacity of 2.8 cubic meters / 740 gallons. The boiler was equipped with a lining of fireproof brickwork in the area of the firebox. After correcting various teething problems, the locomotive turned out so well that by 1981 all the locomotives of this class were converted accordingly. Yet, several months after the conversion the USSR reduced deliveries of oil to the GDR drastically and at the same time the price was increased substantially. This caused the DR to convert the locomotives back to coal firing as soon as 1982. This conversion was ended in the spring of 1984 and oil firing on these locomotives became history.