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"Could you suggest if and how I can reduce the viscosity of a mineral oil? For example, I have an oil with a viscosity grade of 68 and want to change it to a viscosity grade of 32. I know one way is to mix it with the same grade of oil from the same producer of a lower viscosity. Some have suggested mixing it with fuel."
When it comes to lubrication, an oil's viscosity is considered the most important parameter. The main function of a lubricating oil is to create and maintain a lubrication film between two moving metal surfaces, and this function is dependent on the oil's viscosity. Always ensure that the viscosity of the oil in use meets the original equipment manufacturer's recommendations.
When mixing oils, it is important to consider the desired viscosity as well as the lubricant's compatibility with the diluting product. Not only is there a risk of incompatibility but also of losing the protective film the oil is providing at a viscosity grade of 68.
Mixing fuel with oil is not recommended, as the fuel would not have the same formula as the lubricant. In addition, the flash point of fuel is very low compared to that of a lubricant, which could create a fire risk.
Today's high-performance lubricants are formulated with a carefully selected balance of performance additives and base stocks to match the lubrication requirements of the equipment in which they are used. When lubricants are mixed with fuel or different lubricant types, this balance is often upset. Mechanical problems leading to shorter equipment life can occur.
If you have checked the equipment manufacturer recommendations and lowering the viscosity of the oil is an option, the best recommendation would be to use a lubricant of the same brand and product line with a lower viscosity. In this case, it should be an oil with a viscosity grade lower than 32.
You can find charts on the internet to help identify the correct blending proportions. For instance, if you mix an oil with a viscosity grade of 68 and an oil with a viscosity grade of 22, the proportions needed to attain a viscosity grade of 32 are 35 percent of the oil with a viscosity grade of 68 and 65 percent of the oil with a viscosity grade of 22.
However, there are several concerns to keep in mind when blending different oil viscosities. These would include calculating the right proportions in terms of volume instead of weight, mixing the oils properly to get a uniform mixture, and utilizing clean containers and a clean environment so as not to contaminate the lubricant with airborne particles or moisture.
After completing the mixture, measure the viscosity of the blend to ensure you have achieved your target. You may also wish to test the viscosity again after several hours in operation.