It has a lot more life then the oil with the TBN of 5 and if the TBN was high because it was not doing its job that should show up in the oil report.

 

Not so. TBN is not the only indicator of oil life. Oil has many functions, and neutralizing acid is one of them. High TBN reserve doesn't mean your soot levels are acceptable, that your additive levels are still correct, or that the oil hasn't oxidized heavily.

Moreover, TBN should be decaying quickly if the rate of acid production is quick. If contaminant acid production is low, TBN depletion should be slow.

There are several kinds of weak acids (carboxylate precursors) that are insufficient to be neutralized by most TBN additives. In this case, the higher TBN level indicates it is not doing its job because it would be lower (used up) if it was neutralizing the carboxylate precursor weak acids.

I've seen oil filters nearly plugged with junk caused by acids when the TBN of the oil was well over 5.0.

Your faith in TBN is misplaced. There is no fountain of youth for oil. You cannot filter out ALL the bad stuff, nor can you neutralize ALL the acids. The idea that oil never "wears out" is good marketing, but simply false. You have to change your oil eventually to get the junk out.

JH

 

I see the point you are trying to get across now. In theory a higher TBN should net you greater longevity, but that isn't always the case.

Do you have an explanation for the known issue of copper being leached into the oil because of the oil cooler?

No one should extended the drain interval unless they do an analysis also. I still change my oil around the 25,000 mile mark even though it could be run longer according to analysis. By this time the filter is pretty much used up anyhow.

 

Copper, Zinc and neighboring metals on the Periodic Table are just pretty reactive in hot oil.

My understanding is that the copper leaches out as a copper salt caused by a copper alkaline compound reacting with weak acids.

If I remember right, we had some experience that suggested that above certain piston temps, copper in the oil would cause hard carbonaceous coking to build up underneath the piston (where the PCN blast would hit it). This would reduce the effectiveness of the PCN cooling and eventually fail a piston because of the snowball effect.

I think this resulted in changing to aluminum for oil coolers because the stainless cores had to be brazed (read: copper).

Different ratings and other other engines may use the stainless cooler cores still because the pistons don't operate hot enough to experience this deposit tendency.

My understanding is that the copper doesn't leach into the oil coolers but FROM them.

My experience suggests (imo) that it is preferable to not have copper touching any fuel or oil. That's why brass fittings for fuel or oil are no-nos!

Extended drains tend to aggravate higher copper levels.