Oil Tech: Acids & Bases

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Apr2012 24



Let me preface this first installment of our Oil Tech series by saying I am definitely the engineer type, and the years I’ve spent in the automotive industry have led me to ask a lot of questions about how things work and why things happen. So, how does the oil in your engine work? As i learn more about lubricants and their properties, I’ve become almost overwhelmed by the complexity of the duties the oil in your engine performs. Each new post will discuss another important factor in your oil’s performance, longevity, potential issues, or just things I find cool about lubricants.

Why does oil wear out? A good question that has crossed the mind, at some point, of almost every automobile owner on the road. As I mentioned, there are several things that affect your oil’s ability to perform. Today we will address a property known as stability.

Oil stability is, just as it sounds, the ability of the oil to remain stable. What does that mean? The combustion process is a complex mix of chemistry and thermodynamics. The combination of the byproducts of combustion, namely heat and gasses, work together to create a very harsh environment for your engine oil. This can have many negative effects on the oil, but today we will be focusing on oxidation and acidity.

When oil oxidizes it creates carboxylic acid. In some engines, the presence of sulfur (more common in diesels) can also combine with combustion gasses to create sulfuric acid. Either way, the presence of acids in the oil is not good, as acids are corrosive and can react with the metals in your engine.

This is addressed by adding a base to the oil to neutralize the acid. Typically the added base would be an alkali metal or alkaline earth metal, and the measurement of base in the oil may be referred to as alkalinity. This would be part of the additive package in the oil, and calcium is a popular antioxidant/anti-corrosive additive in lubricants.

The best way to test how much life is left on an oil is to have an oil analysis done where the TBN, or Total Base Number, is measured. Just as it sounds, this is a measure of the reserve alkalinity, or how much acid-neutralizing capacity the oil still has.

There are also several oil additives that have increase the TBN, one being BG MOA which contains calcium, among other lubricating and detergent additives.

Stay tuned for the next installment, where I will be discussing viscosity and oil sludge.

For the complete series of Oil Tech posts, check out this link

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