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"If we use an engine oil with a high base number, can a commercial engine cleaner help remove sulfated ash from the valve seat?"
The base number of an engine oil is directly linked to the oil’s reserve alkalinity and in particular the overbased detergent additives. These additives help neutralize acids produced with reactions of the fuel in blow-by gases as well as acids that naturally occur with the breakdown of the oil’s hydrocarbon structure. Detergents also serve another purpose by cleaning deposits that are built up in engine components.
Calcium sulfonate is a common detergent additive found in most engine oils. When these additives are burned, an ashy residue can be left behind. Under normal conditions, this ash is not enough to cause concern, as it can be removed in the next oil change. This becomes a problem when oil changes are routinely ignored or the oil drain intervals are overextended.
All engine oils start with an initial base number that is proportional to the amount of detergent additives blended into the oil. A high initial base number means that more of these detergent additives are present in the oil. As the oil ages and acids are produced, the base number declines. This drop in base number becomes a concern when it decreases to nearly 50 percent of the original value. This is the optimum time to perform an oil change. If the oil is left in the engine, it can begin to turn more acidic and lead to corrosive damage as well as ash buildup.
Most newer engine oils are formulated with a lower ash content to meet the latest environmental emission standards. This lower ash content coupled with the lower sulfur content in fuels has greatly reduced the tendency for ash to build up. However, if the oil is allowed to remain in service beyond its usable service life, ash buildup is still possible.
The problem with commercial engine cleaners is that they are chemically aggressive and can strip additive films off components, leading to increased engine wear and damage. These additive films are important to maintain to ensure the engine is protected on startup when lubrication relies solely on the additive film.
Engine cleaners may also have adverse effects on the oil, such as lowering the viscosity and neutralizing additives. A better strategy would be to clean up the ash by mechanical means and then perform a series of short oil changes to allow the detergents in the oil to clean the engine over time.