Running Amsoil S2k 0w-30. How low should I let TBN go. Also how far out of viscosity should I go?
TBN - When to change
- Thread starter archryhntng
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Any oil should be changed when TBN drops 50% or so. TBN number alone doesn't indicate that the oil provides enough protection. An oil with TBN=5 can be corrosive if the initian TBN figure was above 10. As a rule of thumb 40% still works fine but not much lower.
Ded's answer is incorrect. TBN is an absolute number that is a determination of the amount of residual acid neutralizing capacity remaining in the oil. Oil with a TBN of 1 is no more corrosive than oil with a TBN of 12. The problem is that when TBN reaches 0, things go down hill very fast with rapid accumulation of oxidation products (sludge) and accelerated surface corrosion when the engine sits idle.
Blackstone and apparently a few other companies make a systematic error in TBN measurement. A Blackstone TBN of 1.0 is safe but makes a good endpoint. A TBN of 2.0 would be a concern for UOAs from other companies such as OA. But the oil usually would be condemned for other reasons before the TBN gets that low unless you are running very high sulfur fuel. With an oil that starts out with a TBN of 10, you can think that the oil still has approximately 20% of the original acid buffering capacity remaining when the TBN reaches 2.0. It's not quite that simple, but the statement illustrates the principle.
Blackstone and apparently a few other companies make a systematic error in TBN measurement. A Blackstone TBN of 1.0 is safe but makes a good endpoint. A TBN of 2.0 would be a concern for UOAs from other companies such as OA. But the oil usually would be condemned for other reasons before the TBN gets that low unless you are running very high sulfur fuel. With an oil that starts out with a TBN of 10, you can think that the oil still has approximately 20% of the original acid buffering capacity remaining when the TBN reaches 2.0. It's not quite that simple, but the statement illustrates the principle.
I appreciate your remarks but the only thing I agree with is that TBN is an absolute number. Unfortunately TAN is also an absolute number. As soon as TAN exceeds TBN an oil is junk no matter what your feelings are.
What are we seeing if the starting TAN is 2.08 and the TBN is 5.1 .... new oil ?
I concur with Buster and Ded. I think both mentioned that there are other factors to consider also. Depending on which lab you use, you will get different data and maybe different recommendations.
If you are using OAI, I like Buster's response and keep your eye on oxd and nit. If the TBN is 5 or below, vis is high 40, and Oxd and Nit are over 20% it is time to change.
Blackstone does have a startlingly low TBN reading and I don't think the tell you Oxd and Nit. They do however provide a lot more commentary.
Good Luck and let us knwo what the numbers are.
Don
TBN was 2.7 with 22000 miles on oil. Was going to try and run for 35,000 but looking like I might have to change it. UOA is listed on UOA section of site. Concern was potassium. I listed it as 58. This was a typo. It is actually 6.
They are all wrong and part right.
I am not a language expert and don't have the patience to get into it with the
LITTLE that I do know...
BUT
THERE are ERROR factors with TBN as well...
Now take the fact that if you were wise you'd have some buffer level in there..
Then take into account that not all oils drop or start out with the same TBN
And not all TBNs are the same...
You may get a TBN that shows virgin at 10 but in fact that is the BOTTLE ### and if placed into the car it is a real 9 or 8
And some drop very fast and some are steady drops
others the TBN will hold then DROP more than in the beginning
And yet others have somponents that help keep the falling TBN boosted up longer over time so here it could go from a 10 to a 9 to an 8 to an 8.5 to an 8 to an 8.4 to an 7.9 to a 8.2 to an 7.0 back up to an 8.0 to a 7.5 to a 6.9 to a 6.2 to a 6.9
as an example...
SO unless you know how YOUR oil responds and what it looks like in your engine at "X" miles
then it's just a yardstick.
a Rule of thumb or whatever you call it.
Me.. I have posted about this before... but give yourself some legroom... that's my opinion.
Oil is a CHEAP insurance policy, use it and when in doubt... throw it away
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