Oils will list a TBN figure on their spec sheets.
Total base number.
The engine oil gets acidic with use and time. Time is related to the amount of condensation and condensation cycles. Moisture slowly makes the oil acidic.
Mobil 1 oils usually have TBN numbers close to 10.
TBN dropping is not linear. It usually drops to half or so fairly quickly, then levels off.
Blackstone labs will test for TBN if that box is checked. They recommend changing it when it drops to 2 or below.
If you really want to know how long you can go, send off a sample.
My opinion is it can go years. With short trip driving, It it not getting the oil upto 100c or so for at least 25 minutes that causes the TBN to drop because of not enough time to burn off condensation.
Short generator exercise runs might be considered as similar duties to short trip driving.
