To understand why some mixed lubricants work and others don't, you need to understand the base oil and additive chemistry of the lubricant and how they are formulated. Most lubricants consist of:
Base oil as the lubricity portion
- Common mineral oils with impurities
- Synthetic oils like PAOs, esters and glycols
Additive packages as the lubricant performance enhancers
- Acidic additives
- Basic additives
Lubricants made with synthetic base oils should not be mixed with products made with mineral oils, even if they are designed for the same application. The exceptions are some PAO and ester based products. Additives impart special performance features to the finished lubricant. The choice of additives and the balance among them differentiates an antiwear oil from a turbine oil.
Lubricant incompatibility is a chemistry problem and has nothing to do with the manufacturer of the lubricant. Some lubricants are incompatible because of differences in additive chemistry that lead to undesirable reactions:
- Acidic component + basic component
- Salt (Soap) + Water
- Salt (Soap) + Oil
- Grease-like Suspension
If these oils are mixed, insoluble materials may form and deposit onto sensitive machine surfaces. For a hydraulic fluid this could lead to clogged filters, lubrication starvation, valve failures or increased wear. In another form, incompatible lubricants may attack synthetic rubber seals. Too much seal swell, seal shrinkage or chemical deterioration may occur with some combinations of lubricants.
Before mixing different lubricants, the general rule is:
If in doubt - don't mix!
If mixing of different lubricants occurs accidentally, bring in an expert, whether it is the lubricant manufacturer, the additive supplier or an independent consultant to address the problem immediately.