Flashpoint Testing

Engine Oil Analysis – Detecting diesel engine fuel through Flash-point analysis?

When you see a flame, what you are seeing is a burning mixture of Fuel & Oxygen. The Flash-Point of a material is the lowest temperature in which the vapours coming from the material will ignite as a fuel, given an ignition source (for example; a spark.) This is not to be confused with an Auto-Ignition Point, the point where a material self ignites without a source of ignition; or a Fire Point, the temperature where the material will keep burning once ignited.

Flash point analysis can be extremely useful in determining if a volatile/flammable material has contaminated a known material, or whether the oil is degrading and producing these contaminants. The reason is that as more of the flammable material contaminates the sample, more of the fuels vapour will be present when the oil is heated, which in turn depresses the Flash point of the material. 

If a material has a flash point far lower than it’s specification, there would be strong evidence to believe that either the oil is no longer working as intended; Or contaminated by an undesired fuel/volatile material such as Petrol or diesel.

Engine Oil Contaminated By Diesel Fuel

The oil in your diesel engine can be badly affected by fuel contamination. Diesel & Petrol fuels act as a thinner to your engine oil, causing the viscosity to drop dramatically. As we point out in the viscosity section, an oil’s viscosity is one of the single most important defences against abnormal wear and/or equipment failure.

Should the flash point indicate the presence of diesel or petrol fuel, then it may suggest that fuel is entering the crankcase by way of the combustion chamber. This is called blow-by. Another cause of fuel dilution is by raw fuel entering the crankcase due to dripping faulty injectors.

The flash point test works hand-in-hand with the viscosity test, and together they can help us tell the difference between an oil thinning due to oil transfer/degradation and an oil thinning due to the presence of diesel fuel/petrol.

OCLS uses three Setaflash Series 3 closed cup flash testers, renown for their accuracy and durability.