# TBN Depletion and Retention in Engine Oil



## XtremeRevolution (Jan 19, 2012)

Moved out of Gearhead section and into Powertrain.


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## jblackburn (Apr 14, 2012)

So what's considered "too low" by most? 2? 3?


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## XtremeRevolution (Jan 19, 2012)

jblackburn said:


> So what's considered "too low" by most? 2? 3?


Oil Analyzers and Blackstone both view anything below 1.0 as being too low. At that point, there is almost no detergent left to neutralize acidity and acidity is about to start rising rapidly.


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## jblackburn (Apr 14, 2012)

XtremeRevolution said:


> Oil Analyzers and Blackstone both view anything below 1.0 as being too low. At that point, there is almost no detergent left to neutralize acidity and acidity is about to start rising rapidly.


Right, that's a critical level - so what do most people recommend actually changing the oil at before it becomes acidic at that point? I see they flagged it there at 3; would it get a more severe flag at or under 2 to suggest changing it?


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## XtremeRevolution (Jan 19, 2012)

jblackburn said:


> Right, that's a critical level - so what do most people recommend actually changing the oil at before it becomes acidic at that point? I see they flagged it there at 3; would it get a more severe flag at or under 2 to suggest changing it?


My research has shown that oil does not become critically acidic until there is too little TBN left. That critical point is less than 1.0. At 1.0, the oil is not considered critically acidic and the detergent package is still neutralizing acidity. Oil analysis reports will usually try to give you some kind of information regarding when you can get another sample so they will flag it once it drops below about 1/3 or 1/4 the starting value. However, a flagged value in oil analysis that isn't critical is generally considered to be a trend that should be observed, not a reason to change it. Keep in mind analysis companies, for liability reasons, will always err on the side of caution because they don't know your conditions or the rate of TBN decay in your specific oil. Once TBN drops below 3.0, most companies will just recommend that you change it as they have no idea how much longer it will last as every oil is formulated differently and will have a different rate of TBN decay. 

Oil Analyzers inc specifically told me the oil isn't flagged as critical till it drops below 1.0. I personally would change it once it gets below 2.0.


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## Jim Frye (Mar 16, 2011)

Excellent information! I think I'll stick with following the OLM of my car and change the full synthetic oil when it gets down below 15% (around 6,500 miles so far) as recommended by the manufacturer. I've run my prior cars on 10K OCIs with no problems, but with E0 so non-existent on the street around here, I'll just play it safe.


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