Extension of Oil Change Intervals
Extending oil drains without considering the consequences can cost a lot in engine life. Here we can see two examples of trash trucks where they decided to change the oil every 600 hours of work, regardless of the oil quality.
The first example is a bolivian oil, straight from the drum before use. We can see that the additives do not come close to what they should. It has about 20% of the detergent/dispersant required and 30% of the anti-wear additives. The viscosity does not match what is on the label (15W-40).
The detergent started 80% lower than it should, and is now only 3% of what the engine needs.
The anti-wear additives have decrease to 5% of normal.
The TBN (reserve against acids and corrosion) has dropped to less than 0.5. This does not protect anything. This problems passes on to the next oil, as the sludge accumulated in the engine has to be cleaned up by future oil.
Bolivian oil with 611 hours of use
In reality the oil is not supposed to have to clean up all the mess made by the last oil, but it did eliminate 62 ppm of iron along with the other sludge it took off the walls of the engine.
A good North American oil with 611 hours
Another new Bolivian oil
A new top of the line Argentine oil
At the time, this was the highest grade oil offered in the Bolivian market by this Argentine brand.