Your engine oil change intervals are affected by a waning motor oil base number.

It’s important to understand how engine oil change intervals are affected by a waning motor oil base number: with increasing oil and filter prices, and the cost of repairs, ignoring this can be very expensive.

How are engine oil change intervals affected by a waning motor oil base number?

Base number testing, which measures the reserve alkalinity of the lubricant, is primarily applied to engine oil applications. It is the ability to neutralize acids created during the normal combustion process of an internal combustion engine. As the contaminants build up engine oil change intervals will be affected by a waning motor oil base number.

The base number, which was formerly known as the Total Base Number, can be defined as the quantity of acid, expressed in terms of potassium hydroxide, that is required to neutralize all basic constituents present in a 1 gram sample.

Once the base number reaches 50 percent of the starting value for that lubricant (specifically that batch of lubricant vs. manufacturer spec sheets), the engine oil change interval is affected by the waning motor oil base number. As the base number decreases over time, you can expect the rate of change to increase. This change gives you time to prepare for that increased rate of degradation.

If the base number (BN) falls to about 50 percent of the value of new oil, it’s a good indication that the engine oil change interval is being affected by a waning motor oil base number.

Is there any way of improving the Base Number and reduce the effect of a waning motor oil base number on engine oil change intervals.

Engine oil change intervals affected by a waning motor oil base number can be positively improved by adding about 25% fresh oil to a typical 5lt system, but this can only be confirmed with oil analysis (Note: This depends on several factors, with the severity of the lubricant being the primary factor; and by way of example, 500ml is unlikely to make a significant difference).

This is because you are basically diluting the acids in the sump, with fresh oil. Other parameters on the oil analysis should also be taken into consideration before determining this to be the best route on extending an engine oil change.


Of course, using synthetic oil has the advantage that engine oil change intervals affected by a waning motor oil base number are radically improved. Using a quality full synthetic engine oil, such as that supplied by Habot Oil can safely more than double intervals, under favourable conditions. If you’d like to find out more about Habot Oil, please contact us for professional advice.