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According to Wikipedia,

Total Base Number (TBN) is a measurement of basicity that is expressed in terms of klk number of milligrams of potassium hydroxide per gram of oil sample (mg KOH/g). TBN is an important measurement in petroleum products, and the value varies depending on its application. TBN generally ranges from 6–8 mg KOH/g in modern lubricants, 7–10 mg KOH/g for general internal combustion engine use and 10–15 mg KOH/g for diesel engine operations. TBN is typically higher for marine grade lubricants, approximately 15-80 mg KOH/g, as the higher TBN values are designed to increase the operating period under harsh operating conditions, before the lubricant requires replacement.

But, can be there be a too high TBN?

For example, what could happen if a 10-15 TBN oil was used to lubricate a regular non-diesel car/motorcycle engine, instead of the standard 7-10 tbn one?

ManRow
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1 Answers1

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You might want to read the article here:

TBN Discussion

But the key point on too high a TBN number is:

So should we all use a High TBN oil? There are advantages, but there are also disadvantages of using a High based TBN oil (known as High Overbased Sulphonates) it's not just because the price is much higher. High TBN oils can produce high ash content that can impair engine efficiency and cause loss of power, this will lead to excessive deposit build-up on pistons and valves. High ash is caused by non-combustible residue of an oils detergent additives, these additives contain derivatives such as barium, calcium and magnesium. These deposits can lead to the following devastating results:

> Ash deposit build-up on pistons and valves 
> Loss of oil stability
> Polishing of cylinder line bores 
> Valve Guttering 
> Loss of power
> Increased oil consumption 
> Increased fuel consumption

So the point is, I believe, use the proper oil specified by the engine's manufacturer. If the TBN is a little high, as in your hypothetical case, it's not too much of a concern. If it's WAY high, then you may have problems.

jwh20
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