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#2276038 - 06/01/11 05:14 AM How important is TBN in Choosing an oil ?
vxcalais Offline


Registered: 07/14/07
Posts: 770
Loc: Melbourne, Australia
How much emphasis should be placed on a higher TBN oil for a 10,000 mile drain interval ? I traditionally go for tbn's of around 9 and above etc when choosing an oil. Some oils that have the same oil ratings may only have a tbn of 7 etc. Does this mean less additives or different additives ? For example, most SL/SM CI4 are 9 and above, yet some only have 7 and so on.
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#2276051 - 06/01/11 05:55 AM Re: How important is TBN in Choosing an oil ? [Re: vxcalais]
Colt45ws Offline


Registered: 08/15/06
Posts: 7354
Loc: Central Washington
It depends on the chemistry. Some seem to last longer for a given number than others. I wouldnt base much of anything on the starting TBN.
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2004 Ford Crown Vic LX, 76k "Tank" Back in Service
2002 Ford Crown Vic PI, 160k "Highwayman" (Ex-Kootenai County, ID Unit #42)

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#2276073 - 06/01/11 06:43 AM Re: How important is TBN in Choosing an oil ? [Re: vxcalais]
NateDN10 Offline


Registered: 01/10/10
Posts: 1372
Loc: Rochester, NY
In general, an higher starting TBN is better. However, some are better at TBN retention.

This is one place API SN oils should be better than their SM predecessors, for example.

What I typically try to do is to find UOAs with high mileage (7500+) on the oil to see TBN at that point. That's usually more telling than the starting TBN.
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#2276083 - 06/01/11 06:50 AM Re: How important is TBN in Choosing an oil ? [Re: vxcalais]
Jim Allen Offline


Registered: 08/12/05
Posts: 4477
Loc: NW Ohio
The best way to judge is by comparing starting and ending TBNs, with both the TBN tests done by the same lab. There are several methods for determining TBN and they read a little differently. You want to compare apples to apples with he same test methodology. That means a VOA with the oil you plan to use. A super-high TBN, around 10+, which you would find more common in the HDEO diesel rated oils, are not necessarily a good thing in a gas engine because they may leave more deposits and poison the cat faster (in a nutshell...much more to that). "High" starting TBN in a gas engine is 7-8. But like was said above, some TBNs start a little lower and hold longer and that counts for more than a high number that may drop precipitously.
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#2276084 - 06/01/11 06:54 AM Re: How important is TBN in Choosing an oil ? [Re: vxcalais]
vxcalais Offline


Registered: 07/14/07
Posts: 770
Loc: Melbourne, Australia
Thanks guys, some good advice for me to ponder. Tricky when you see oils with same ratings, claim high additives etc, but TBN's are clearly different.
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#2276130 - 06/01/11 08:37 AM Re: How important is TBN in Choosing an oil ? [Re: vxcalais]
INDYMAC Offline


Registered: 07/15/06
Posts: 2324
Loc: Magnolia, TX
I think the best way to look at this number is by how effective whatever TBN additives are used in the formula, relative to how well it is keeping TAN in check. A high starting TBN, or even reserve alkalinity at the end of an OCI means nothing if the chemistry of the oil allowed acids to build up unsafely. So, in short, don't pick the oil you want to use based on a higher starting or ending TBN alone. How effective the TBN is in use is more important.
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#2276151 - 06/01/11 09:06 AM Re: How important is TBN in Choosing an oil ? [Re: INDYMAC]
daves87rs Offline


Registered: 02/23/09
Posts: 13257
Loc: Michigan
Originally Posted By: INDYMAC
I think the best way to look at this number is by how effective whatever TBN additives are used in the formula, relative to how well it is keeping TAN in check. A high starting TBN, or even reserve alkalinity at the end of an OCI means nothing if the chemistry of the oil allowed acids to build up unsafely. So, in short, don't pick the oil you want to use based on a higher starting or ending TBN alone. How effective the TBN is in use is more important.


Good food for thought.
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#2276241 - 06/01/11 11:08 AM Re: How important is TBN in Choosing an oil ? [Re: NateDN10]
Hokiefyd Offline


Registered: 06/24/04
Posts: 10729
Loc: North Carolina
Originally Posted By: NateDN10
This is one place API SN oils should be better than their SM predecessors, for example.


I'm not challenging your statement, but asking for confirmation. I don't recall anything in the API SN description that would indicate a better TBN retention, but I'll be the first to concede that I could have missed it.
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#2276246 - 06/01/11 11:15 AM Re: How important is TBN in Choosing an oil ? [Re: vxcalais]
NateDN10 Offline


Registered: 01/10/10
Posts: 1372
Loc: Rochester, NY
Oops, my bad. API SN calls for better ZDP retention, and I assumed that would help TBN as well. After a brief search around the internet, it appears that this is not the case.
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2005 Chevrolet Cobalt - 85,000 mi.
2012 Mazda5 - 63,000 mi.

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#2276377 - 06/01/11 02:14 PM Re: How important is TBN in Choosing an oil ? [Re: vxcalais]
dparm Online   content


Registered: 04/19/10
Posts: 12330
Loc: Chicago, IL
It's only one aspect of an oil's performance. I wouldn't let it be the deciding factor.
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der stärkste buchstabe der welt
Castrol Edge Professional TWS 10w60 + Mahle OX 254D3

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#2276423 - 06/01/11 03:41 PM Re: How important is TBN in Choosing an oil ? [Re: Hokiefyd]
addyguy Offline


Registered: 09/08/05
Posts: 13425
Loc: Canada
Originally Posted By: Hokiefyd
Originally Posted By: NateDN10
This is one place API SN oils should be better than their SM predecessors, for example.


I'm not challenging your statement, but asking for confirmation. I don't recall anything in the API SN description that would indicate a better TBN retention, but I'll be the first to concede that I could have missed it.


API SN protocol DOES call for oils to be able to handle E-85 fuels better. Higher alcohol levels, AFAIK, lead to higher contamination of the oils. Oils would have to retain TBN better to be able to handle E-85 fuel, so this first statement is correct.
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2003 Mazda Tribute LX V-6, 164k miles.
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