Diesel vs. Gas Engines... The Reality

Most diesel engines in small and large trucks generally operate at mostly a constant speed and higher load factors than gasoline engines do. Therefore internal combustion conditions are more optimum, and water condensation and fuel dilution is not as serious as a problem as in a gasoline application.

Fuel Dilution Worries -
Where excessive fuel dilution occurs, it is usually the result of a mechanical problem, such as a faulty injector or other fuel related problem. Diesel fuel is not as readily evaporated from the engine oil lubricants, as is gasoline; therefore, if a problem exists, the concentration of diesel fuel will tend to increase at a more consistent level. This can lead to deposits and reduction of the oil viscosity to a sufficient level that mechanical and abrasive wear occurs.

Diesel Sulfur Concerns -
One of the major problems and concerns with diesel engines is the sulfur in the diesel fuel. Sulfur is present in diesel fuels at a higher concentration than in gasoline products. When diesel burns, it forms sulfur dioxide, part of which may be further oxidized to sulfur trioxide.

A Word about Deposits -
In combination with water, these sulfur oxides form strong acids that are not only corrosive in themselves but also have a strong chemical effect on the engine oil degradation. Since cylinder temperatures are also higher, this may result in heavy deposits of carbon, soot and varnish on the pistons, valves and in the ring grooves. Under heavy operating conditions, deposits may build up in the ring grooves to the point where the rings cannot function properly, and high wear, blow-by, and loss of power may be noticed from the output of the engine and its operational mode.

Soot Increases Drain Intervals -
Manufacturers of diesel engine passenger cars are particularly concerned about soot deposits and recommend more frequent oil drains than in larger diesel applications (recommendation every 2000 miles for longer engine life) more than twice those required for gasoline fueled car engines.

The Corrosion Equation -
Many large diesel engines in marine and industrial service are operated on residual type fuels, such as low sulfur fuels with sulfur content in the 2 to 4 percent range, and in some cases natural gas which can reduce build up of soot and carbons up to 75% less then of diesel fuel. But always remember the acid levels of the higher sulfur fuels that are formed from regular combustion, can be extremely corrosive to rings, liners, pistons and valves in all applications and sizes of engines.

The Big Switch -
One last thing is to watch is the time of year that gas stations and diesel fuel suppliers switch from number 2 diesel to number 1 diesel. This is mostly for you subscribers that live in cold climate areas. You may loose mileage and performance of what you were getting from number 2 diesel. It takes about 18,300 BTU (British Thermal Units) to burn 1 lb of fuel. The most optimal burn comes when you reach 19,400 BTU's per pound and this may require a fuel additive or fuel catalyst to achieve proper performance from your diesel fuel.

We would like to say thanks to George Wills, for the input of this week's LubeTalk.

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