Foothills Antique
Tractor and Engine Club

These cheaper fuels included "distillate" and kerosene, and they were obtained from a heavier fraction of the crude than gasoline during the refining process.  The boiling points of distillate and kerosene are higher than gasoline, and the energy content per gallon is also slightly higher.  However, the octane ratings were lower, thus a lower compression ratio is necessary with a carbureted engine to prevent damaging pre-ignition (knock or ping).  It is the lower compression ratio that causes the distillate, kerosene and all-fuel engines to have lower fuel efficiencies than gasoline engines.

Since distillate and kerosene do not vaporize as readily as gasoline, and starting on these fuels is difficult or impossible when the engine is cold.  The remedy was to add a second, smaller gasoline tank and a selector valve so the operator could start the engine on gasoline and warm the engine to operating temperature, then switch to the low cost fuel.

Proper warm-up is essential when operating on lower grade fuels.  First, the engine, especially the manifold, must be warm enough to vaporize the fuel for a good fuel-air mixture that ignites and burns efficiently.  But, a warm engine is also necessary to prevent condensation of the fuel on the cylinder walls.  Fuel condensation on the cylinder walls will dilute the lubricating oil and result in accelerated engine wear.  Recommended operating temperature is 190F for all-fuel and kerosene engines.  In fact, 190F is the recommended operating temperature for most modern engines, and the parts are designed to have the proper dimensions and clearances at 190F coolant temperature.  A hotter engine can also be more fuel efficient because more of the energy delivered by burning the fuel is converted to useful work.  To operate an engine at 160F wastes a lot more energy as waste heat than operating at 190F.

Why are all-fuel engines no longer made?  As the cost of gasoline approached that of distillate, all-fuel engines were discontinued in favor of gasolines that have higher compression, and are therefore more powerful for a given displacement and also more fuel efficient.  Occasionally, you'll see LP fueled tractors, and these were high compression, powerful tractors in comparison to all-fuel tractors.  Eventually diesel engines became the preferred power plant, and you cannot buy new gasoline powered agricultural tractors today.  Modern diesels are more fuel efficient, require less maintenance and have a longer operating life than gasoline engines.