I do believe every one is entitled to their opinion and without that, this would be a boring world, I will stick to my beliefs and of course you can stick with yours, as any subject is open to debate, never will you get a decisive answer as there are too many variables with large and small engines, as I said I would rather 1/2 the service intervals which isn't going to hurt your pocket, where a blown engine certainly would. Heavy engines use an oil spinner to increase the oil life, believe me you should see what these little gems catch. I believe that Land Rover also introduced a Spinner on their TD5 engine when first introduced, funnily enough to extend the oil change.

I will also introduce the argument if you should use a flushing oil or a flushing oil additive mix before changing the oil, please don't, as some of this mix will remain behind in the sump and hydraulic lifters, thus de grading the fresh new oil.

 

I used ELF NF900 5/40 the last 300000km change every 20000km together with diesel filter. Drive patteren was 200km every day. Now it's only 25km a day and I change it every 6. month. I dosen't used a drop between oil change and has now don 485000km .
My motto stick to the same oil brand or you can get big time problems.

 

This is true for older vehicles like the voyager. But not true for vehicles with diesel particulate filters (DPF) fitted. When the filters block up,the vehicle does a regeneration. It usually does this by injecting fuel on an exhaust stroke and burning all the soot out. However,some of the fuel washes down the cylinders and dilutes the oil. Eventually this degrades the oil as diesel does not flash off that same as petrol. Bering in mind the oil has to cool and lubricate the turbo,I would suggest a maximum of 10K mls maximum oil change frequency.

 

The myth, and it is a myth - a country specific issue engineered by people who sell oil. It does not happen in all countries or even most countries. Clean oil is always better than dirty oil but what constitutes dirty oil. We used to have crude oil that worked in crude engines and severe conditions on roads, we have sophisticated engines and similarly matching sophisticated oils and filtration for them and tarmac roads stretching across the globe. Technology has changed much in only 30 let alone 50 years but the 3,000 change-mantra still exists.

How your drive is, for example dustbowl, typical urban, motorway counts as does drive duty such as travel to work or taxi & deliveries duties. For most people the vehicle manufacturers figures are proven by science and million of dollars in research and good enough for 99% of owners. Lifestyle is also a consideration. Retired I only manage 2.5k miles a year and change my oil every 3 years in line with the vehicle manufacturers figures of 12km, along with good filtration [most of the 'sheds' sell garbage filters] - you can add a substantial 'half-life' to any oid change interval by changing just the filters every half oil change interval. When I was working it was fully synthed every January when any convenient day had a 'Y' in it.

 

This was new for me and I did some research on this oil dillution thing.
It seems only certain car brands (like VW) with newer dieselengines suffer from that and only the diesels using the "post-injection method" to clean DPF.
And only when using a diesel mixture with high percentage bio diesel.
I stumbled oversome tests by MB in which they concluded that with a functional DPF the current (long) OCI advice stays in place, I guess the dont use the post injection method hehe.

Personally I would rip out the DPF to be sure

 

I read oil not only degrades by use but also with age. So changing every 3 years, no matter the mileage seems wise to me.

Me, I do like 750 miles a week lately so I stick with long OCI because otherwise my mechaninc gets far too rich

 

Unfortunately an MOT fail.
As you say VW and MB have the add blue (Bluetec) that adds a fluid as you drive (bit like 2 stroke bike I have ) and in theory gives a cleaner burn.