Extending oil drain interval (ODI) by definition is saving, if it is double, saves 100% on lubricant cost, if tripled even more!! But why not many organisation do it??
A leading multinational, lubricant supplier had conducted a trial reported by SAE in 1998. 59 diesel engines, run with several cycles of forced extended ODI, till it clocked 500,000 miles, when finally the engines were inspected.
The key objective was to see the performance difference between “fighting grade (FG) mineral based CG-4” vs “premium grade (PG) fully synthetic CG-4” oils, when both are extended.
For OA, the key parameters are KV @ 100oC, TBN, Soot, Water In Oil, Flash Point, Wear Metals (Fe), and Additives depletion, with sample interval every 10K miles.
- Viscosity: FG can last till 50K, PG is stopped at just before 80K.
- TBN: FG drop close to 50% after 40K, PG is stopped before 80K.
- Fe: Linear increase mostly, though FG start to have higher rate of wear after 20K. (More prominent on Pb.)
- Engine Inspection, where deposits, sludge and visual wear are rated, even for FG, with ODI at 50K are rated very good after more than 10 cycles.
Extended ODI in most cases are not a problem. PG can be extended longer then FG, but not indefinitely.
However, there are exceptional cases which need careful consideration and extending ODI without careful monitoring is risky.