Above: overlay corrosion. Contaminated lube oil possibly very low TBN.
Below: Kittiwake's DIGI Cell provides a simple digital test for TBN levels in diesel oil .
Info Centre >> Fuel and Lube Oil Technical Manual >> 7. Lube Oil - Test Results >> 7.2 Diesel Engine Oil >> 7.2.5 Total Base Number (TBN)
TBN levels in diesel oil
The oil is continuously exposed to acidic combustion products and these must be neutralised before they can corrode engine parts. With distillate-fuelled engines, the sulphur levels are typically < 1% and the alkaline reserve of the new oil is seldom higher than 15 TBN. Typically, it is between 8 and 10 TBN. Engines operating on heavier residual fuels are exposed to a more corrosive combustion regime, as fuel sulphur levels are typically 2 to 4%.
Here the TBN levels are typically between 20 and 40 dependent on fuel sulphur level. In engines where oil consumption is low, TBN may be as high as 50 or 55 in order to limit TBN depletion rates.
As with cylinder lubricants, the overbasing impacts both alkaline reserve and detergency and is of particular importance in the piston ring packs where detergency will provide cleaning and prevent varnish formation on metal surfaces.