Why TBN increased in Used engine oil?

BN measures detergent alkalinity (reserve) in crankcase oil. The crankcase oil will suffer a loss of alkalinity due to acid generation in the crankcase causing a drop in BN. Thermal degradation and fuel/water dilution will also cause a drop in BN.
Typical rule-of-thumb caution levels for BN is 50% of the new oil BN. So if the new oil BN is 10, the caution limit should be set at 5 and a critical BN level of 2. For trending of used oil use ASTM D974, D4739 or D5984-96.

Kelly,

One cummon reason to a BN increase in used oils is the tup ups. Every time you add new oil to complete to the right level, you are also adding new additives. Ask to you maintenance people to keep you updated with the top up date and volume.

TBN increase can be attributed to three reasons.

1. Top up by higher TBN oil
2. Fuel dilution
3. Water dilution

Engines with large sumps like in Diesel Generator sets/Marine engines (auxilary) and using poor fuels have the TBN boosted by topping up with higher TBN oils.

In the Marine engines of MANN, Wartsila etc., TBN is monitered regularly. If due to fuel dilution or water ingress the TBN drops, then the oil is not thrown away. In such cases "sweetening" is done, some quantity of used oils removed and top up is done by higher TBN oils.

Hussam Adeni

When not attributed to an addition of a higher TBN oil, look for evidence of a coolant leak. The Reserve Alkalinity of many coolants and supplemental additives will increase the TBN measurements.

If the BN in used engine oil has increased, please check the following:

1. Is the correct sampling procedure observed? We need to ensure that the sample is truly representative of the bulk oil being sampled. Also, the sample should be taken before any make up oil is added.

2. Please check if the instrument use to test the TBN is working properly. Likewise, check if the person doing the test is properly trained.

Thank you all very much, so long no come here. sorry for so later reply. Your inputting are very useful. Say thanks again. Kelly

quote:

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Originally posted by Kelly:
i havn't been working on used oil analysis for a long time. now, there's a trouble that sometime i found TBN increased surprisingly in Used engine oil. I don't know why?
Hope somebody can help me and tell me why? and how it happend?
Your kindly answer would be appreciated! Thanks a lot!!

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In addition to all possible answeres posted here, there is a another possible occasion that can happen, that is when engine is running extremly hot and if engine oil is a multigrade one, some portion of lighter end base oils can evaporate and thus additive concentation increases. If this happens, TBN and additive metal percentage will increase. This kind of situation would occur very rarely. kumartr@petrominoils.com Kumar

Temperature is definitely a large factor. Either way you look at it.

Used Engine

Depending on the sump capacity I would highly suspect that top up oil could be the cause of your TBN increase. I would speak with the lube tech's and see how much they are adding in between oil samples.