You cannot mix Synthetic oil and mineral oil – or, can you?

Are "old" and new technologies compatible?

Many people will have you believe that the consequences of mixing synthetic and mineral oils are catastrophic.

But the truth is, the effect or consequence, depends on the types of synthetic bases that are mixed with the mineral bases. Polyalphaolefin and diester synthetic bases can quite happily be mixed with mineral oil bases. This is actually how “blended” products are created.

When should synthetic oil and mineral oil not be mixed?

Polyalkylene glycol (PAG) bases should not
be mixed with any of the others unless specialized barrier fluids are used to minimize the incompatibility. When PAGs are mixed into other lubricants, you’ll often get strong negative reactions (producing sludge and tacky residue) that require additional processing to flush, clean and correct.

Even if the base oils are compatible when mixing synthetic and mineral oils, there is a possibility that the additives used to produce the required performance properties could conflict, resulting in a loss of lubricant effectiveness.

It is advisable to perform filterability, oxidation stability, air release and demulsibility testing prior to mixing lubricant intentionally.

Remember, modern lubricants are sophisticated products, formulated to meet the demanding lubrication requirements of modern equipment. The old saying, “oil is oil” no longer applies.

Mixing lubricants is fraught with danger — to your equipment, to your business and to your wallet. When in doubt, don’t mix different lubricants. If it occurs accidentally, address the problem immediately.

In its mildest form, mixing synthetic and mineral oils could lead to a loss of lubricant performance.

What happens if I inadvertently mix synthetic oil and mineral oil in my car engine?

Mixing the same API grades of synthetic passenger car motor oil and mineral oil-based engine oil won’t damage the engine, but you will lose the performance features you expect from the synthetic.

Is there a test I can conduct to determine if I’ll have a problem mixing synthetic and mineral oils?

You can conduct some simple tests to confirm an oil mixing problem even without access to a formal lubricant laboratory:

• Heat the synthetic and mineral oil mixture or the two oils you want to test for compatibility, and examine for clarity. 
• If the mixture is cloudy, the oils are not compatible. 
• To check further, add a small amount of water, mix thoroughly and continue heating. 
• Allow the mixture to sit at room temperature for several hours. 
• If a solid forms in the oil, they are incompatible.

Your response to a situation where synthetic and mineral oils are mixed will depend on the products in the mixture, the end-use application, the relative concentrations of products and the total volume involved.

When dealing with mixing synthetic and mineral oils, don’t be afraid to bring in an expert, whether it is the lubricant manufacturer, such as Habot Synthetic Lubricants, the additive supplier; or, if needed, an independent consultant.