Molybdenum in oil analysis can come from various sources, which include the following:
1. Molybdenum Grease Contamination: This would likely cause increased wear and might also result in higher particle visibility during analysis.
2. Ring Wear: Some engines have molybdenum-coated top rings designed to handle high temperatures. Checking with the engine manufacturer can confirm if this is the case for a specific engine.
3. Molybdenum as an Additive: Molybdenum disulphide is used as a solid lubricant in some oils, similar to how graphite functions. It works synergistically with other anti-wear additives. While only a couple of oil manufacturers used this additive in the past, its use is growing, making it less reliable as an indicator of ring wear.
4. Natural Occurrence in Crude Oil: Molybdenum can naturally occur in crude oil, but its levels are typically reduced significantly during the refining of Group I mineral oils so usually to have anything significant you would have to have issues in the cleanup process.
5. Coolant Leaks: Molybdenum may also appear in used oil due to coolant leakage, as molybdates are used in some coolant formulation, but usually the earliest indicator would be sodium or potassium as the major corrosion inhibitor additive
The best way to assess molybdenum levels is by comparing the used oil to the new oil. Some variation may occur due to oil oxidation and volatilisation of the lighter fractions of the base oil. If there is a significant difference, it is worth investigating whether the oil manufacturer has recently changed the formulation, or whether the oil is a blend of multiple lubricants due to top-ups rather than complete oil changes.