How high is too high for TAN?

[thor2010]

Hi,

I have a Honda Civic with a CVT transmission. I plan on figuring out what is a good transmission fluid OCI using UOAs.
When interpreting these UOAs what TAN level is considered the borderline which if crossed it is time to change the oil?

Thanks.

 

[MolaKule]

I would say three times the starting or VOA TAN.

If you start off with a TAN of 1, then 3 or 3.5 would be my condemnation limit but you say you're going to do UOA's so let the analysis company monitor your limits.

Since there is no combustion to deal with the only reason TAN should rise is you oxidize the oil or somehow get too much moisture in it.

Remember, the important thing here is Trending with at least three samples using the same oil and brand. You cannot get any reasonable results with a one sample snapshot.

 

[thor2010]

Thanks for the help MolaKule.

I posted an UOA for my transmission oil and I would appreciate it if you looked at it.

Thanks again.

 

[btanchors]

This is interesting info...I had been initially concerned about what I thought were high TAN levels in the Front and Rear differentials and transfer case of my 2006 Toyota Tundra, as they were coming in at over 5. But I had a VOA performed on the oil I was using (Amsoil Severe Gear 75W-90) and it came out at 4.3!

MolaKule - isn't that a rather high starting point for a Gear Lube? According to your rule of thumb, that would mean a condemnation limit of 12.9. I don't think I have ever seen a TAN half that amount.

 

[MolaKule]

Quote:
This is interesting info...I had been initially concerned about what I thought were high TAN levels in the Front and Rear differentials and transfer case of my 2006 Toyota Tundra, as they were coming in at over 5. But I had a VOA performed on the oil I was using (Amsoil Severe Gear 75W-90) and it came out at 4.3!

MolaKule - isn't that a rather high starting point for a Gear Lube? According to your rule of thumb, that would mean a condemnation limit of 12.9. I don't think I have ever seen a TAN half that amount.


The simple answer is: No, we are talking about two different types of lubricants,; you're comparing apples and oranges.

Those Amsoil gear lubes have rather low TAN numbers.

ATF and CVT lubricants contain an Anti-Wear additives with low sulfur and phosphorous components.

Differential lubes contain Extreme pressure additives with high levels of S-P chemistry which contribute to high TAN's.

Here are some references you might find interesting:

https://bobistheoilguy.com/forums/threads/synchromesh-manual-transmission-lubricants.93561/

https://bobistheoilguy.com/forums/threads/gear-tribology-and-lubrication-part-ii.57858/