Is oil just oil or can different lubricants be mixed?

Users sometimes wonder if two different engine oils may be mixed. An article from Machinery Lubrication gives a good explanation on this topic.

In general, all lubricants are formulated to meet international specification, such as ACEA, API, etc. So mixing them should not present a real problem, but may lead to loss of performance. Why is that?

If in the past the statement ‘oil is just oil’ could have worked well, recent lubricants represent fine-tuned mixtures of tenths of components, adapted to sophisticated equipment. There are many different ways of formulating the oil in order to obtain a specific level of performance.

If we just look at the base oils used in a lubricant, it could be that we find polyalphaolefins (PAO) and esters there, which are compatible with mineral oils. But other base oils, like polyalkylene glycols (PAG), are not. Mixing a PAG-based oil with a mineral one will give sludge and residue.

Even if the synthetic base oil used in a car engine is compatible with the mineral product, some amount of the superior performance of the synthetic will be lost. There is also the potential danger of a conflict between different additive chemistry used in the different oils. Additive manufacturers spend years to obtain a balanced, highly performing and stable additive package.

And at the other side of the spectrum, mixing oils which were intended for different applications may lead to wear and plugging and cause serious damage.

In conclusion: avoid mixing different oils. Make use of the Wolf lubricant finder on our homepage and select the right oil for your application.

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