R 707, which due to various defects had still not been put into service by 1954, was selected for modification for precipitated brown coal (PBC) operation in conjunction with trials of this fuel being undertaken with X class 'Mikado' X 32.
Dynamometer car tests with R 707 showed the locomotive was able to develop approximately 1,590  drawbar horsepower (1,186 kW) at 37.5 mph (60.4 km/h), roughly equivalent to the 1,605 drawbar horsepower (1,197 kW) generated by a conventional R class locomotive burning second grade Lithgow black coal.
However, comparative tests also demonstrated that R 707 also achieved considerably higher efficiency, capable of consuming 1.5 tons less coal on the 200-mile (320 km) Melbourne to Bendigo round trip hauling a 350-ton trailing load, despite the lower calorific value of brown coal than the Lithgow coal.
While the PBC locomotives performed well, the expense of installing storage and handling facilities became increasingly uneconomic with falling prices for fuel oil and the success of diesel-electric traction.
The conversion had also reduced the water capacity of R 707's tender such that there was insufficient margin for delays or bad weather running on many routes, confining the locomotive to the shorter Melbourne to Geelong and Seymour lines.
The experiments were discontinued and R 707 was converted back to black coal operation in 1957.

R 719 and 748 were converted to oil-firing during the mid-1950s using oil tanks and burner equipment salvaged from the four scrapped S class steam locomotives.
They performed very well and were  favourites among crews for their clean, cinder-free running.
The reduced maintenance associated with their oil-fired operation meant they also had the highest availability of any of the R class and as such recorded the highest mileages of any of the class.
 However, rising fuel oil costs and the ongoing dieselisation program on the VR precluded any further locomotives from being converted.
R 743 was in the process of conversion to oil firing as part of a major overhaul in February 1957 when instructions were issued to halt the conversion program and was returned to service as a coal fired locomotive.
R 707, which due to various defects had still not been put into service by 1954, was selected for modification for precipitated brown coal (PBC) operation in conjunction with trials of this fuel being undertaken with X class 'Mikado' X 32. Dynamometer car tests with R 707 showed the locomotive was able to develop approximately 1,590  drawbar horsepower (1,186 kW) at 37.5 mph (60.4 km/h), roughly equivalent to the 1,605 drawbar horsepower (1,197 kW) generated by a conventional R class locomotive burning second grade Lithgow black coal. However, comparative tests also demonstrated that R 707 also achieved considerably higher efficiency, capable of consuming 1.5 tons less coal on the 200-mile (320 km) Melbourne to Bendigo round trip hauling a 350-ton trailing load, despite the lower calorific value of brown coal than the Lithgow coal. While the PBC locomotives performed well, the expense of installing storage and handling facilities became increasingly uneconomic with falling prices for fuel oil and the success of diesel-electric traction. The conversion had also reduced the water capacity of R 707's tender such that there was insufficient margin for delays or bad weather running on many routes, confining the locomotive to the shorter Melbourne to Geelong and Seymour lines. The experiments were discontinued and R 707 was converted back to black coal operation in 1957.
R 719 and 748 were converted to oil-firing during the mid-1950s using oil tanks and burner equipment salvaged from the four scrapped S class steam locomotives. They performed very well and were  favourites among crews for their clean, cinder-free running. The reduced maintenance associated with their oil-fired operation meant they also had the highest availability of any of the R class and as such recorded the highest mileages of any of the class.  However, rising fuel oil costs and the ongoing dieselisation program on the VR precluded any further locomotives from being converted. R 743 was in the process of conversion to oil firing as part of a major overhaul in February 1957 when instructions were issued to halt the conversion program and was returned to service as a coal fired locomotive.
Victorian Railways R class