Quote:
Originally Posted by Zebster
But why would diesel be left in the cylinder to run down into the sump? The fuel injection would cease immediately when the vehicle 'ignition' was switched off, even though the engine would then still undertake a few revolutions due to momentum that would clear the cylinders. In any case, even if the last spurt from an injector was left in one cylinder then it'd only be a fraction of a CC, so it seems unlikely that this tiny amount could cause the sump volume to increase by 0.5L (e.g. the alarm level) even after time.
Surely such a significant amount of diesel being accumulated in the sump is far likely to be caused by one (or more) leaking injectors, potentially allowing the entire pressurised volume in the rail to be discharged?
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It's not just the small amount of fuel left in a cylinder when the engine is switched off. It is a continuous process that happens during regeneration cycles.
https://www.jstor.org/stable/26273272
I'm no expert, but the issue affects many more vehicles than Volvo. It seems that vehicles which have the DPF situated further from the engine are prone to greater problems, partly because it is more difficult for the engine post-injection cycles to achieve suitable DPF temperatures to complete the regeneration cycles.
My Volvo is a petrol car, but I know that many diesel vehicles including my van can suffer from oil dilution. My van has a built in software algorithm that monitors a variety of sensors and external conditions, from which it "calculates" (guestimates) the likely conditon/dilution of the oil due to the number and type of regeneration cycles, and displays a warning when or if it considers that the oil should be changed before the normal service interval. If the warning is ignored, the vehicle enters limp mode a short time thereafter, and if further ignored, refuses to start until the system has been reset - hopefully following an oil change, but some owners are just resetting the warning system without changing the oil by following YouTube type instructions and because they don't understand the logic!
Modern DPF compatible oils are engineered for use with up to something like 9% oil dilution by fuel, from memory, by which time however they are often barely capable of meeting the grade criteria from what I have read.