automotive Archives - Strategic Reliability Solutions Ltd

The TBN has dropped significantly, can I still use the oil?

The TBN (Total Base Number) is usually seen in diesel engines. Most modern (smaller) diesel engines have TBNs within the range of 9-15 (especially if they are using ULSD).

The TBN gets depleted when the acids in the oil start to increase.

Typically, higher sulphur levels in the fuel produce more acids. As such, as the sulphur level increases, so does the TBN level.

For instance, in power plants that use larger (older) diesel engines that require HSFO (High Sulphur Fuel Oil, 3.5% sulphur), the TBN of the lubricant can be as much as 50. Here are the different types of fuel and their sulphur ratings:

HFSO (High Sulphur Fuel Oil): 3.5%
LSFO (Low Sulphur Fuel Oil): 1.0%
ULSFO (Ultra Low Sulphur Fuel Oil): 0.1%

With IMO 2020, the cap has been placed on sulphur in fuel to 0.5% for marine vessels. While this cap has not yet been translated to land applications, due to the demand for HSFO declining there may be a shift to ULSFO in land based applications in the not so distant future.

Ideally, if your TBN level gets depleted by 50% then there is a cause for concern and the oil should be changed or topped up with new oil (depending on which is more convenient).

If your TBN levels get to 50% in a very short time, you may want to investigate the reasons behind the value dropping so significantly in such a short time (perhaps fuel dilution or thermal cracking?).

Always investigate the reasons behind unexpected results as these will continue to impact your lubricant in the future.

What does the “w” stand for in multigrade oils?

The “w” stands for winter.

Let’s go back a bit. We weren’t always as advanced in lubricant technology as we are today. For instance, if we left an ice tray filled with water on the table, what would happen? It would remain in that state of water. Now, if we placed that in the freezer, the water would turn into ice.

Similarly, before we advanced lubrication technology, there was one oil to be used for the Summer and one for the Winter. During the summer, the temperatures were higher and during the winter the temperatures were lower.

The “w” helps us to understand that this is the measurement related to how an oil flows at a cold temperature (or on start-up). It does not mean that you can only use an oil with a “w” in countries that experience winter!

The lower the number is in front of the “w”, the faster the oil flows on start-up. When we start our cars on a morning, all of the oil is at the bottom of the sump. It will take some time before the oil gets from the bottom to the top of the engine.

However, all of the parts in the engine are moving before they get the oil. Thus, it is critical to get the oil to them in the shortest time possible. The lower the number in front of the “w”, the faster the oil takes to get to the top of the engine (this will reduce the amount of wear that occurs).

Quick Tip: Zero (0) does not mean that there is no protection on start up, it means that it will get to the components faster than all the other grades (like a 0w20).

What about the number after the “w”?

This is the number that represents the viscosity of the oil at operating temperature. When the engine begins operating this is the viscosity that flows through all of the lines and components continuously. As we mentioned in an earlier post, the value has decreased in recent times (some going as low as 0w16!) due to the lines being thinner, which is ideal for lower viscosities.

Tagged: automotive

TBN decrease

That “w”!