Built_Well, I think TomNJ, Molakule, Dyson, and RL_RS4 may be the only guys out there that can tell you "how high is too high" re: TAN in ester-based oils.
I know I have been researching this for quite a while and have been annoying Molakule and TomNJ with Q's about how TBN and TAN in ester-based oils work.
We know that oils such as Redline and Biosyn can simultaneously have both high TBN and TAN. I know for me one of my redline runs (90% city, all approx. 1-2 mile trips with no time for engine to warm up) my tan was I think 5.7 and that felt on the high side to me. Comments from the experts for that run felt that it was not "corrosive" with a TAN that high, but that 5.7 was on "the high side".
Also please look at TomNJ's entire post, not just that one line, such as:
"
Indeed some of these fatty acids act as corrosion inhibitors! The acids liberated from the degradation of hydrocarbon base oils, however, are much stronger and corrosive. Hence I would expect a different set of rules for ester based oils to allow more TAN than with hydrocarbon based oils."
"while I have seen recommendations from some manufacturers allowing as high as 5 to 8 TAN before changing for ester oils."
"Without field data to the contrary, I would tend to ignore TANs in high ester based motor oils so long as other UOA data is normal."
The main point here I guess is that ester-based oils have a different set of rules when it comes to TAN and TBN. And interpreting those rules accurately is for the moment beyond the level of knowledge of most of us. A 2nd and 3rd run would make it much easier to tell what is going on with Pb levels, IMO.
I guess all the above is leading up to exactly what Rl_RS4 said, if you want to know if high TAN is related to your Pb levels, and if that should be of concern, have Dyson (or some other expert) look at it. I do very much appreciate the discussion though, as I really want to understand this stuff!