How to distinguish mineral oil from synthetic


I bought a used car and I don’t know what kind of oil: mineral or synthetic oil is poured, for example, in a gearbox. Is there a certain way to distinguish mineral oil from synthetic without sending samples to the lab? What happens if these oils are mixed or topped up with the "wrong" oil? "

Usually dye affects the color of engine oil. There are no standards for determining the color of motor or transmission oils, and manufacturers can produce a product of any color. Unfortunately, there is also no reliable way to differentiate between mineral and synthetic oils "by eye".

However, synthetic base oils are clear. Mineral base oils have a darker natural color due to aromatics, sulfur and other impurities. This can be a distinctive factor.

It should be noted that despite the transparent color of the base synthetic oil , additives in it may add color, such as darkening. And the finished synthetic oil will also have a dark color.

In the laboratory, it is easy enough to distinguish synthetics from mineral oil. Learn the combination of the following physical properties, such as:
- viscosity index
- flash point,
- pour point.

Laboratory tests can also draw conclusions based on differences in the chemical additives of the tested oils.

Most likely, synthetic gear oil will be based on polyalphaolefins (PAO). They are very similar chemically to mineral oils, and mixing with mineral water should not cause compatibility problems, especially if both oils are the same by API classification.

Problems may arise when the mineral oil is inadequately filled in, where only synthetic oil is required, for example, to operate the engine at a cold ambient temperature. Using mineral oil by mistake, you can expect problems with the morning engine start.

Important! Some synthetic gear oils are based on polyglycol ether (PAG) base oils that are chemically incompatible with both PAO synthetics and mineral oils. In this case, mixing will lead to serious problems.

What happens if these oils are mixed or topped up with the "wrong" oil?