Dirty Fuel

Dirty fuel makes its presence felt in a very marked way, usually involving rough running and often stoppage of the engine. Severe contamination will not only stop an engine, but keep it stopped until it has been dismantled and cleaned out. There are two main types of contaminants—foreign matter, such as water, rust and dirt, and fuel-derived contaminants formed by the interaction, under abnormal conditions, of elements contained in the gasoline.

Occasionally a mysterious temporary fuel blockage will occur through the formation of ice-crys-stals in water held in suspension in the fuel, but this usually clears itself as heat soaks back from the engine.

Since customer reaction to dirty gasoline is usually fairly strong, suppliers run constant checks on cleanliness from refinery stages right up to the point where it is pumped into cars on service station driveways. Even small amounts of contamination can reduce a high quality gasoline to one of comparatively low standard.

Even in the good old days, volatility was taken as one of the most important basic requirements of a satisfactory gasoline. They even had a disarmingly simple test for this property. You took a can of petrol up to the second storey and poured it through the window. If enough of it reached the ground to make a splash, then the petrol wasn't good enough. Needless to say, somewhat more refined techniques have been adopted.

The subject of volatility is one that is fraught with hazards. For instance, it would be natural to assume that the greater the volatility, the better the petrol. It would also be wrong. During winter periods, a high degree of volatility would certainly help cold starting, because the temperature at which the petrol vapourises is low enough to combat the atmospheric conditions.

But in summer, this high volatility would mean that the fuel vaporised too readily, causing vapour locks in the feed lines, and a consequent blockage of fuel from the carburettor.