MolaKule
Staff member
Can you have too high an alkaline reserve? I.E. can you use too high a TBN oil?
From, the "Tribodetective Case Files"quote:
The Case of the Overbased Engine Oil:
A maintenance superintendent of a landfill gas burning power plant contacted us some time ago and asked about engine oil base numbers. He figured you can never have enough protection.
Q: Use of a higher base number (BN) oil if you can afford it. Is this a good way to maintain your engines?
A: No. You can actually destroy an engine solely by using a higher than needed base number engine lubricating oil. Total base number (TBN or BN) is a measure of the reserve alkalinity additive present in the oil. It is designed to neutralize harmful acids produced as the byproducts of engine blowby. What many engine owners don’t often realize is that the strength of this alkaline reserve package is tailored to the sulfur content in the fuel. It is not uncommon to see high levels of sulfur in large marine, landfill, or power generation applications, and as such high TBN oils must be used to combat the highly corrosive blowby gases entering the crankcase. Whereas most users understand and use the higher TBN oils for these sour fuels, if your sulfur content decreases, you must decrease your TBN number also. The following example illustrates the danger of not doing so.
Several years ago, a large reciprocating engine plant serving several Boston hospitals ran into this problem 1. The situation occurred when they were changing lubricants, and the suggestion at the time was to use a high detergency 24 TBN oil, even though their No. 6 fuel oil sulfur content remained at or below 0.5%. The cleaner blowby gases resulted in more alkaline reserve additives remaining in the oil. In the presence of water, these excess carbonates recrystallize to form larger particles, which in turn are carried to cylinder walls. A reaction with combustion gases occurs here, producing calcium sulfates. These products cling tenaciously to the cylinder walls, and look like a slate/stone like deposit (known as slating or furring). These deposits are very abrasive, and promote bore polishing, eventually leading to piston seizure.
The current efforts to use cleaner, low sulfur fuels nowadays means that engine owners need to consult their lube supplier when the fuel properties change substantially, so as to recommend the right matching lubricant. Make sure to analyze your engine oil properly on a frequent basis.
-DPW
1: Seifert, W., Westcott, V. Santoro, S., “Systemic Evaluation- An Integrated Approach to Machine Condition Monitoring”, P/PM technology, Vol 5, Issue 1 pp 17.