Oil mixology

John Baxter | July 01, 2010

Because additives decompose, the only way to replenish them is with a fresh oil change. No matter how effective oil filtration is, it does not replenish depleted additives, Alexander says. “Nor does fine filtration remove contaminants from combustion by-products, fuel dilution, acids, etc.,” he says. “And, extending drains beyond the OEM recommendation could invalidate your equipment warranty.”

As key components of engine oil get depleted or altered, the need for an oil change increases, Dias says. For example, acids produced in the combustion process deplete the oil’s TBN (total base number) or increase its TAN (total acid number). “Under extremely severe conditions, one might see a slow depletion of zinc and phosphorus,” he says. “In such cases, if the analysis indicates that oil has reached condemning limits, it is advisable to change the oil even though the standard drain has not been reached.”

Oil analysis says little directly about additives’ effectiveness. The additive list in an oil analysis report lacks sufficient detail for you to be able to evaluate the additive package, though it has some relevant information.

Alexander says a good report “should have pertinent parameters measured – that is, wear metals, TBN, TAN (total acid number), soot, viscosity, fuel dilution, water/glycol, etc. – and include condemning limits to alert the user of impending problems.” If the report suggests problems, the oil should be changed soon. If the problem persists, the situation should be investigated until resolved.

The key piece of information is the presence of wear metals. “Wear metals will tell you if oil additives are working,” Arcy says. “Also, the report will list contaminants like sodium and potassium that should not be there.”

Using over-the-counter additives is risky. “We discourage people from using oil additives,” Arcy says. “They can disrupt that balance we’ve put into our products.”

This Caterpillar C15 run on Shell Rotella T4 for nearly 670,000 miles shows negligible sludge on the top surface of the cylinder head – a surface that’s very hard to keep free of deposits. Quality oil includes detergent additives that keep combustion byproducts dissolved so they cannot attach themselves to engine parts.

By going with a quality engine oil that has been thoroughly tested, and changing it based on lab analysis or manufacturer guidelines, your engine will be more likely to last a million miles without a breakdown or major repair. And, you can rely on the additives even though you may not fully understand how they work. n

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