OCI and TBN

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miniac007

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Hi all,

When I use UAO to optimize the OCI, I have read I should change oil when:

- TBN < 35% of its initial value

- or when TAN cross over TBN


But, on Blackstone VAO, they seem considere a TBN over 1 is OK.

So I don't understand where is the truth !


Whith a initial TBN of 10, should I change oil at 3.5 or at 1 ? It is very different...
 
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I don't think there is one clear cut answer to this, unfortunately. Every lab will have a different policy on this.

Personally, I would not wait until it goes below 1.
 
You definitely want TAN to be lower than TBN, which I prefer to be above 2. The lowest reading of TBN on my Amsoil Oil Analysis' has been 4 after 10k (over a 16 year period).

For other oils, above 2 will provide a better safety margin.
 
Originally Posted By: 147_Grain
You definitely want TAN to be lower than TBN, which I prefer to be above 2.

Typically, by the time your TBN gets down to 2, your TAN is already way above 2 at that point. Many modern oil chemistries result in fairly high TAN to begin with. Take PU 5w-40 which I'm using in my 530i as an example. VOA showed it had TAN of 2.14. By the time I hit 6K miles on it, TAN was up to 3.8 while TBN was down to 3.6. The lab flagged the oil's condition as 'abnormal'.
 
Thank you for all your answer. If I resume:

- First, we must know the TAN of the VOA. On group I/II/III should be near 2. One IV/V, it can be near 6.

- We only can use TAN/TBN criteria with a low initial TAN.

- So, with oils with low initial TAN, near 2, we cannot let the TBN go under this TAN.

- Then if we have the TAN of the VOA, we use this value to change oil when TBN fall under, and if not, we don't let the TBN fall under 2/2.5

Is that OK ?


So with gasoline oils and a initial TBN near 6, this criteria of 2 match the 35% of TBN. But with HDEO with a initial TBN of 10, this criteria of 2 is far after 35% of the initial TBN.

Then, if we want someting accurate, it seems we have to do a VOA and UOA with TAN+TBN to calibrate the new oil and see exactly when TBN cross TAN, and note at what % of the initial TBN it occurs. When it is calibrated for this specific oil and usage, we can use this % of initial TBN to set OCI without need of TAN each time.

am I right ?
 
I can't answer your question about TAN, however....I use the OXID and NIT vs. the TBN and VISCOSITY LCM method. Meaning, as your OXID and NIT rise, your TBN and VISCOSITY fall. Or your VISCOSITY Climbs....So when you meet the ceiling on OXID and NIT and your TBN and VISCOSITY are LOW or VISCOSITY is Hight.....change the oil and filter.
 
I posted here the UOA of my tractor

The TBN fell down from 10 to 2.3; 2.3 is over 2 but under 3.5 (35%), and the lead seems high that indicate acid corrosion...

So, in that case, 1 or 2 seems to be to low.
 
Finding out the initial VOA TBN is fairly easy (If you can't find it in this forum, it might be in the oil data sheet), so because it's important for a diesel to be kept clean I use the one third of VOA figure. Some labs that quote a min figure are silly, because if you don't have the TAN there is no real way of knowing the exact min figure, so it's best to play safe. One third of VOA will be between 2 (New high tech synthetic using Magnesium?) and 4 (Good HM or HDEO).
 
Originally Posted By: miniac007
Hi all,

When I use UAO to optimize the OCI, I have read I should change oil when:
- TBN < 35% of its initial value
- or when TAN cross over TBN
But, on Blackstone VAO, they seem considere a TBN over 1 is OK.
So I don't understand where is the truth !
Whith a initial TBN of 10, should I change oil at 3.5 or at 1 ? It is very different...

As an example - according to Nissan fleet test limit TBN should be more than 1 mgKOH/g after 20000 km in EU or after 15 000 km outside EU for PCMO.
I think your criteria are for HDMO, where soot content could be reach 4-5% in oil and TBN/TAN balance is very critical to keep soot.
 
Interesting hypothesis. So >1 should match for gasoline cars.

But [censored] does'nt distinguish between cars, truck, gas or diesel, HDOE or not... Always 1 ...
 
Originally Posted By: miniac007
Hi all,

When I use UAO to optimize the OCI, I have read I should change oil when:

- TBN < 35% of its initial value

- or when TAN cross over TBN


But, on Blackstone VAO, they seem considere a TBN over 1 is OK.

So I don't understand where is the truth !


Whith a initial TBN of 10, should I change oil at 3.5 or at 1 ? It is very different...


I used to work for MTU and my understanding is that if you want to keep a big diesel clean the min TBN is one half of the VOA figure, BUT for a car diesel it is one third of the VOA figure. I'm not sure if there is a difference for gas engines, but I can't think why it would be different to the one third figure.

Blackstein's are talking nonsense to quote a figure of one, because if you want to go below the third of VOA figure then you should pay for a TAN check, because it's very difficult to know if the detergents and dispersants are still functioning with low TBN numbers. Once the TAN and TBN cross the oil starts to dump Carbon out of suspension, but that could be anywhere from 0 to 4 in absolute TBN numbers.
 
Last edited:
Thanks for the interesting doc, Miniac.

You find things like that regularly for HD diesel engines, i.e. specific MAx/Min oil condition recommendations from an engine manufacturer, but seldom do you find such things for gas engines. And basically never for passenger car/light truck (though I'll bet most mfrs have something).

Swiss, I think that is where Blackstone (Blackstein ( : < ) which reminds me of the old Mel Brooks, "Franken-schtine vs Franken-schteen") get's their "1". Plus there are other "tells" in a UOA. But Like you, I have never been fully comfortable with seeing a "1" but I think it also may have something to do with their lab equipment and experience. With their setup, the "1" works reliably. Overall, I do not like to compare samples from different labs for this reason.. unless I know absolutely that they are the same page in their labs.
 
Originally Posted By: avss1
Cummins recommendation for TBN of HDDO:
2.5 number minimum or half new oil value or equal to total acid number (TAN)
http://www.kleenoilusa.com/pdf/warranty/Cummins-Oil_ServiceBulletin_May-07.pdf


I think their TBN recommendation is a sound one, BUT the comment about bypass filtration keeping contaminants low enough to prevent wear is nuts.
Bypass filtration is good news, BUT my guess is that the best it will do is to increase the main block life by 20%. The reason is simple, only 10% of the oil is filtered in one pass on average, so if a particle enters the oil stream it has a very high chance of getting stuck between the bearing rollers and cage or rings and piston before the fine filter has a chance to catch it. Bypass filtration is much more effective at keeping the soot level low enough for the OCI to be extended significantly, but it's effect on engine wear is within the tollerance limits for what is normal variance for the life of the bearings.

In other words if you had a normal full flow filter and short OCI's, the main block might only last 20% less than the average figure for a bypass filtered engine, BUT the life expectancy of the main bearings will vary by upto 25% (Depends on the quality control to a minor degree). This means that there is no guarantee an individual engine will last longer, as lady luck will have her say at the end of the day.
 
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