Diesel Stationary Engines: Pre-War Versus Post-War Fuel Consumption

For collectors, restorers and rural operators across Australia, fuel use remains one of the most telling indicators of an engine's condition. A diesel stationary plant that burns two litres more per hour than the manufacturer's logbook figure is usually telling you something — worn injectors, dirty air filter, tired pump, or simply an outdated combustion chamber design. The Peter and Rita Forbes archive at stationary-engine.net holds decades of logged figures from British makers like Lister, Ruston, Petter and Crossley, and many of those readings were taken in conditions not far removed from the dusty yards of the Riverina or the wheat belts of Western Australia.

What follows is a working comparison of fuel consumption between pre-war and post-war diesel stationary engines, drawing on the kinds of measurements a restorer might record during a weekend rally or a station owner might keep in the back of a notebook beside the bore pump. The focus is on litres per hour at common loads, the practical effect of fuel quality, and what Australian conditions — from the chilly mornings at Injune to the heat shimmer over a Pilbara shed roof — actually do to the numbers.

Defining the Two Eras and Their Engine Designs

The pre-war diesel stationary engine is generally considered anything built before 1939, with many survivors dating from the mid-1920s onwards. These were predominantly slow-revving horizontal units, often started by cartridge, decompressor or compressed air, and many relied on indirect injection or air-blast injection systems. Combustion chamber design was conservative, compression ratios modest by later standards, and the engines were built with considerable mechanical tolerance. A Ruston of 1934 or a Lister of 1932 was expected to run on whatever fuel came out of a drum at a mine site or a railway siding.

Post-war designs, from roughly 1946 onwards, took advantage of lessons learned in marine and tank propulsion. Direct injection replaced air-blast systems in most small and medium stationary sets, compression ratios rose, and combustion chambers became more efficient. Makers like Perkins, Lister-Petter and English Electric produced compact verticals that ran faster, smoother and noticeably more economically. The Australian National Maritime Museum in Sydney holds representative examples of both eras, and so does the working collection at the Australian National Heritage-listed Coal Mine Historic Site in Tasmania, where Ruston and Hornsby horizontals still turn over for visitors on demonstration days.

Measuring Fuel Use: Methods Then and Now

In the pre-war and immediate post-war decades, fuel consumption was usually measured with a tin can and a clock. An engine would be run on a calibrated drum for a timed hour at a known load, and the fall in the fuel level recorded by hand. The result, often in imperial gallons per hour, was then compared to the maker's published figure. That method is still used at heritage rallies from Ballarat to Bundaberg, where restorers set up their machines on a test bed and trade figures over a cuppa at the club shed.

Modern measurement is more refined. Turbine flow meters, hour meters with trip functions and even ultrasonic inline sensors now let a station owner log litres per hour continuously. Electronic logging is particularly helpful for operators on remote holdings in places like the Kimberley or western Queensland, where a diesel plant may run twenty hours a day on a solar-diesel hybrid scheme. Whatever the method, the principle is the same — you cannot manage what you have not measured, and the figures from the old logbooks are still the benchmark against which a restored machine is judged.

Cold Starting, Warm-Up and Idle Consumption

Cold-start behaviour is one area where the gap between the two generations is most visible. A pre-war horizontal often needed ten or fifteen minutes of hand-cranking, decompressor work and patient warming before it would accept much load, and during that interval it was burning fuel at a disproportionate rate relative to the work it was producing. Decompression losses, partial combustion and rich starting mixtures all inflated the early-hour figures.

Post-war engines arrived with improvements that addressed this directly. Glow plugs and heater plugs shortened the cranking period, injector nozzles sprayed fuel more finely, and combustion chambers tolerated cold starts far better. On a frosty morning at an antique rally in Mudgee, the difference between a 1930s horizontal and a 1950s vertical at start-up can be measured in minutes and in litres. For outback operators running bore pumps through winter at places like Cunnamulla or Hay, those savings matter at the end of the financial year.

Specific Fuel Consumption at Common Loads

Specific fuel consumption, expressed as litres per kilowatt-hour or grams per kilowatt-hour, is the cleanest way to compare engines of different sizes and ages. Pre-war diesels typically sat between 0.45 and 0.55 litres per kilowatt-hour at rated load, with figures considerably worse at low load where the combustion chamber design struggled to burn the fuel efficiently. A 7 kWh Ruston might burn somewhere between 3 and 3.8 litres per hour when properly loaded.

Post-war engines closed the gap. By the mid-1960s, a well-set Lister-Petter or Perkins stationary diesel would return figures in the region of 0.32 to 0.40 litres per kilowatt-hour at rated load, and the spread between full-load and half-load economy narrowed noticeably. A 10 kWh post-war unit might comfortably sit at 3.5 litres per hour at continuous rating, where its pre-war equivalent would be working hard to stay below 5 litres. The published figures vary, but the general relationship holds: post-war designs are roughly 20 to 30 percent more frugal at the same shaft output, with the gap widening sharply at part load.

Fuel Quality, Cetane Rating and Local Conditions

Fuel itself has changed almost as much as the engines. Pre-war diesel was often a heavier fraction with higher sulphur content, modest cetane ratings and greater lubricity. It smelled different, stained hands faster, and left more residue in injectors and on cylinder heads. Post-war engines were designed for cleaner fuel, and modern Australian pump diesel has gone further still — Australia moved to ultra-low sulphur diesel as the standard grade in 2009, with most regional bowsers now delivering less than 10 parts per million of sulphur.

That change has consequences for older plant. ULSD is kinder to emissions but harsher on certain elastomer seals, and bush mechanics from the Atherton Tablelands to the Esperance sandplain have learned to keep a wary eye on fuel filter seals and injector return lines on restored engines running supermarket diesel. Cetane ratings are typically higher than they were in the 1930s, which actually helps ignition in older chambers, but the lower density can throw out fuel-rate calculations by a couple of percent. The figures in the old logbooks, almost always in gallons per hour, must be converted using local density if you want to compare them honestly with what the meter reads today.

Maintenance Practices and How They Affect Burn Rate

An engine's fuel appetite is rarely fixed by its year of manufacture. Injector condition alone can swing consumption by 10 to 15 percent, and a clogged air filter or a tired fuel lift pump can push figures higher still. Pre-war engines tend to be more tolerant of neglect — wider tolerances, heavier castings, fewer precision parts — which is why so many survived in remote service long after they would have been pensioned off in a workshop. The trade-off is that worn examples often never recover their original figures, even after a full restoration.

Post-war engines reward careful maintenance. Clean fuel, fresh injector tips, correct valve clearances and a properly set governor can bring a 1962 Petter back very close to its maker's figure. Australian restorers in regional centres such as Toowoomba, Wagga Wagga and Hamilton have built a strong tradition of methodical rebuilds, and at club days the conversation often turns to whose engine returned to its logbook figure and whose did not. The answer usually lies in the precision of the injector work rather than the age of the iron.

Restoring or Running a Vintage Diesel Today

For anyone taking on a stationary diesel, the practical path is simple. Start by logging what the engine actually burns at no load, half load and full load, using a calibrated container and a stopwatch if no meter is fitted. Compare those figures with the maker's original data, which is widely available in the older literature and increasingly on archival sites such as stationary-engine.net. Then look at the small things first — air intake, fuel lift pressure, injector spray pattern, governor response — before assuming the engine itself is the issue.

For detailed help on identifying a particular model or sourcing historical data, the contact page maintained by Peter and Rita Forbes is a useful starting point, and many Australian restorers have used it to chase down workshop manuals that never made it into general circulation.

Practical Recommendations for Tracking and Reducing Fuel Use

If you are running a vintage diesel in the Australian bush — whether it is turning a generator on a cattle station, driving a pump on a market garden in the Lockyer Valley, or simply turning over at a rally in Tassie — taking the time to measure and log fuel use pays for itself in the first tank. The data you collect becomes part of the engine's history, and it adds to the wider record that makes sites like this one possible. Get in touch with Peter and Rita if you have figures worth sharing, or if you need help chasing down the original logbook data for a particular make and model.