TBN level and oil age vs mileage

[CATERHAM]

The TBN level of motor oil in service drops predictable with mileage. But does it also drop with age in infrequently used vehicles?
I'm not talking about short trips where the oil doesn't get up to temperature and is contaminated by water, fuel etc. I'm referring to special interest vehicles of one sort or another that are driven infrequently but when they are driven the oil is brought fully up to temperature before the engine is shut down. Annual mileage may not exceed 250 to 3000 miles per year.
Does the TBN level start to decline regardless.
I've seen UOA of high mileage OCI's safely exceeding two years, but what about 3, 4 or 5 years?

 

[pitzel]

Changes in TBN are exclusively the result of SOx and NOx combustion byproducts reacting with combustion moisture, and becoming part of the motor oil.

As long as you don't run the engine, TBN will not deteriorate.

3-5 year oil changes shouldn't be a problem in your engines, if they are infrequently used, and could otherwise tolerate 10-15k mile OCI's.

 

[CATERHAM]

pitzel, that's good to hear.
But, playing devil's advocate; time, a year typically, in addition to mileage is always given as the max' OCI by various sources including oil companies? I've always thought there must be something I'm missing hear?

 

[pitzel]

The 1-year is a generic 'catch-all', for someone who might do a ton of 2-mile trips.

 

[CATERHAM]

And that's "a ton of 2-mile trips" in a Saskatchewan winter, right?

Thanks pitzel.

 

[pitzel]

Well, then you might be into fuel dilution, or even water ingress. Depending on design, the method of fuel induction, etc.