Lube Notes: Petroleum Oil vs Synthetic Oil - Lubrication Wear Protection

Volume 2 Issue 1 - Lubrication

Article Index
Lube Notes: Petroleum Oil vs Synthetic Oil
Oxidation Stability
Lubrication/Wear Protection
Petroleum Oil vs Synthetic Oil: Cost
All Pages

Lubrication/Wear Protection

How well does the oil lubricate and, in turn, prevent wear? Lubrication is a result of both base oil and additive combinations performing in various lubrication regimes in order to prevent metal-to-metal contact and the wear that results. Where fluid film is retained, the base oil will be the dominant factor in lubrication. Where oil film is not always able to separate the moving metal parts, additives become the dominant factor. The uniform molecular structure of synthetics results in a superior lubricating film. Additionally, the thermal stability of synthetic oils maintains an oil film in much more severe conditions – at higher temperatures, for instance – than petroleum. Additives are relatively equal in performance regardless of the base oil – synthetic or petroleum – with which they are combined. Instead, the anti-wear protection they provide – or fail to provide – is more dependent on their own quality and concentration. For normal temperatures, properly additized petroleum oils and synthetic oils will show similar lubricating qualities. Synthetic oils have higher film strengths and require a lower quantity of additives in order to achieve the same level of protection. In standard anti-wear testing such as the Shell four-ball wear test, some synthetics achieve up to four times the wear protection when compared to petroleum oils. When higher temperatures and pressures are used in such tests, the results significantly favor synthetic oils.

>Normal Operational Conditions Advantage: Slightly Synthetics
>Severe Operational Conditions Advantage: Very Strongly Synthetics


Oil Life / Endurance

How long can the oil provide proper lubrication and perform all required functions? Oil life is a function of time and severity of service and can vary from vehicle to vehicle. Oil is said to be condemned, that is, not fit for continued service, when one or more of the following conditions exist:

  • Viscosity has decreased by one grade or increased by more than one grade
  • Fuel contamination is greater than three percent
  • Soot level exceeds four percent
  • Total dissolved solids are greater than four percent
  • Total Base Number is less than two
  • Critical additives are depleted
  • Oxidation number greater than 50 (30 for petroleum)
  • Nitration number greater than 50 (30 for Petroleum)

As explained above, synthetic oils are less likely to thicken as the result of vaporization or oxidation and they stay in proper viscosity grade for significantly longer periods of service. Several of the other factors for condemnation are the same for either synthetic or petroleum oils and are more dependent on the quality and concentration of chemical additives required to continue to provide service. Soot and total dissolved solids are products of engine combustion and are proportional to fuel air management; turbo charged engines tend to burn cleaner than naturally aspirated engines. Filtration, especially bypass filtration, will have direct effects on soot and dissolved particles and can be effective at increasing oil life. Since lubricating oils are products of base oils mixed with chemical additives it becomes painfully obvious that either the failure of the base oil or the depletion of additives will result in condemnation of the oil. Simply put, oils are unique when compared to each other; even if two synthetics are compared, the choice of synthetic base oil and the quality and amount of the additives can produce widely varying finished products.

Oil life is best determined utilizing used oil analysis and then evaluating the remaining oil life based upon the results of a given analysis. Some oil companies, like Mobil and Amsoil have amassed significant data through oil analysis that enables them to make categorical recommendations for longer drain intervals. It is improper to assume that, because you are using synthetic oil, it automatically has an extended drain interval. Some major oil companies – Valvoline is one – are on record as saying their synthetic oil has the same additive package as their petroleum; so, the additives in their synthetic oils deplete just as quickly as their petroleum oils.

> Oil Life / Endurance Advantage: Synthetics (varies between synthetic manufacturer)


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