Mineral oil-based Group I base oils are the least changed during their production process, which is solvent refining. As pure base oils, they are usually only used for applications with relatively low technical requirements, such as recirculating, insulating or heat transfer oils.
Mineral oil-based Group II base oils are usually produced using an elaborate hydrocracking process that removes impurities from the oil. Not only do they have a clearer colour, they also contain more than 90% saturated hydrocarbons. In addition, they contain less than 0.03% sulphur and mostly have a viscosity index of over 90. As a result, they have a significantly higher performance than Group I oils. They are chiefly distinguished by their better antioxidant properties and hence optimised ageing. This also means that less oxidation inhibitors or VI improvers need to be added to Group II-based oils.
New lubricating oil refineries usually only produce Group II oils, because although production is more expensive than that of Group I, manufacturers of finished products can offset the additional costs by saving additives. With the current oversupply of Group II oils, cheaper purchase prices can be achieved. The use of Group II oils is predominantly price-neutral for the user and does not entail any technical disadvantages.
Lubricant manufacturers are also not obliged to inform users of a base oil change by changing the product name or putting a note in the sales documents or data sheet. At OELCHECK, however, such changes stand out immediately due to a direct fresh oil comparison of the oil with the same name a few years ago and today. The additive changes caused by base oil are also evident in trend observations of machines in which only refills are carried out.
If these permissible deviations do not result in any loss of quality, they will not be commented on in particular. Improved ageing stability can usually only be seen anyway by our tribologists in a direct fresh oil comparison with the help of the IR spectrum. The situation is different with defoamer additives containing silicon, which lead to lower silicon values at a lower additive concentration and thus give the impression that less silicon-containing dust is in the oil.
If the elements, the content of the additives or the IR spectrum suddenly no longer match fresh oil or previous trend, this is obviously immediately apparent to the tribologist. However, this is only commented on where there is certainty that this indicates mixing with another type of oil, which could lead to damage if used again.