Dont know if the Victa oil your adding is full "low SAPS" certified or not,
but being at least 'low ash' helps.
The correct and only engine oils to use with DPF fitted engines are formulated specifically for these engines and are of "Low SAPS"...that is low in Sulphated Ash, Phosphorus and Sulphur, but obviously not completely absent.
Also of interest could be if there was the addition of any other additives / potions or concoctions to the fuel of these engines.
Aswell I'd be interested to know what oils were being used by the one's with the complaints.
The 2-stroke I was adding is specifically formulated for 2-stroke motorcycles, and there are 3 grades of that oil: normal, low-ash and high performance (which is also low ash).
The normal oil isn't JASO FC rated, so I didn't bother. The low ash JASO FC-rated Castrol Activ 2T one apparently allows a 2-stroke motorcycle to run without blowing any smoke which is why it's a good choice for adding to diesel engines. The high performance one is used in track racing and I failed to see the point of spending $30 a litre for my purposes when I only needed to have the FC rated oil (at $12 a litre).
As for other additives, I'd be interested in them as well. The 2-stroke apparently raises the combustion temperature by a small amount, but that is enough to more completely combust the fuel during the combustion stroke itself, so there are less particles making it to the DPF in the first place.
The higher temperature would result in the DPF being a few degrees hotter at all times, which means anything caught on the DPF would burn off faster as well. I'm not sure what the temperature difference is doing to the CAT, but since the CAT is removing oxides of nitrogen from the exhaust I'm assuming that the slightly higher temperature is better.
We're not talking a large difference. 300ml over 80 litres is about 0.4% (4ml per litre). That small amount seems to make a decent difference, both in noise levels and in performance. Without extensive figures and only a couple of tankfuls to look at, I'm seeing about 2L per hundred km improvement. Some of that may be environmental.
The quantity of engine oil consumed during the combustion process is going to be less than that, since after 5,000km of driving, there's still most of the oil in the crankcase. The manual shows something interesting in the oil specification:
Diesel engine
API grade CF-4*1, *2
JAS0 DH-1*1
Check that JASO rating - it's ultra low ash content. So Nissan are recommending low ash engine oils. Interesting stuff about the DH-1 oil is in the
reference manual, but it's a heavy read so get your engineering hats on. Basically they describe how DH-1 oils are low ash, low sulphur, high quality yadda yadda yadda.
I bet you're absolutely on the money - the issue with DPF failures may indeed be related to the incorrect engine oil being used. It would be marvellous if one of the guys with DPF problems could give us the exact brand and type of oil used in their crankcase. We might be on to something here!
