Shown graph contains a complete DPF active regeneration process – the rising section (750 seconds duration = 12.5 minutes).
Basically, oil dilution is driven by:
- post-injections during active DPF regeneration
- estimated diesel fuel evaporation
According to internal algorithm and logged data, normal operation does not increase dilution. Oil dilution slowly decreases as the ECU estimates fuel evaporation out of engine oil. (On Euro 4 at least, this algorithm is also running if ignition is on, engine not running but coolant temperature warm enough).
Active regeneration however uses one or more post-injections (small additional late injections – during exhaust stroke) in order to heat up the DPF, raising oil dilution amount, at much higher rate therefore winning over evaporation.
Notice these short intermittent steps during regeneration – these are caused by coasting – ECU suspending all injections, including post-injections.
Wouldn’t coasting cool down the DPF then by pushing rather cold air through the system? To mitigate this, the software fully opens EGR valve (70 deg). As soon as injections resume, EGR valve is being closed again. Normally, during active regeneneration it is in fully closed position (0 deg) helping to increase exhaust temperature (more oxygen).
If you look carefully, you can spot more evaporation going on after regeneration had finished compared to before it started. This is mainly due to higher engine temperature, having reached normal operating conditions of around 90 °C. For evaporation to get going it needs temperatures beyond 30 °C, the higher the better.
Also take a look at post “Estimated Distance to Oil Change” for additional information.