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My take on cetane
It matters very much the older the engine gets. You notice when you have poor quality fuel in a 20 year old diesel, it misfires on start up cold, it makes more noise when starting out. I can always accuse my wife (correctly) when she filled up our 400k mile Jetta at a different station then I like to use (up in Canada Petro Canada has the highest cetane fuel at 45-48). It also shows up in miles per tank, I have 20 years of receipts don't forget which is a pretty strong case. Lower quality fuel we loose 30-50 miles per tank. We run scangauges in all our cars and use a set throttle position to accelerate, about a third. Strictly highway.
With common rail engines it becomes even more critical, injectors do not cost a hundred but closer to five hundred or more each, plus more expensive pumps. On a recent 5000 mile trip when I used known 50 cetane fuel (Southern States gold diesel) we saw a 5-10% increase in fuel economy. I run fuel conditioners and lots of it to try and reduce deposits and increase cetane, but seeing that much increase with just a fuel supply clearly shows it matters. This trip was a Mercedes R320 cdi, common rail. Biodiesel does not offer the same energy content as regular diesel and there is a drop in fuel economy, however usually an increase in lubricity and cetane. Bio does NOT STORE well, so the content of the biodiesel at the pump can swing wildly one tank to the next and it can separate in as little as 6 months and have layers in the fuel.
I try to run a mix of conditioners, ones that offer Xylene, cetane (2-ethylhexyl nitrate), petrollium distillates, others that are not on my mind right now but each company lists a few different blends and I mixem up to get the best of each. I am generally going double dose every tank to try and get the cetane up around 50. All euro diesel require 50 cetane, and benefits are found up to 60 or so and then it tappers off.
What I can offer in my life of driving diesels by using conditioners, injector deposits are much less when servicing injectors (versus clients who do not), I have never had to reseal an injection pump on my vehicles, I have never had fuel related failures or pump failures yet. I only drive diesels. I research who sells what fuel and try to get the best fuel I can, I do not shop on price I do shop quality. I do not believe in using truck stops, they tend to have volume but low quality.
The better a diesel runs on cold start up, the less blowby, the lower particulate matter getting recycled into the egr and intake and lower carbon build up. There is a lot of misinformation on labels and such. VW TDIs with regenerations are set up to regenerate at X miles, the actual build up in the particulate filter does not matter unless there is an issue (it is monitored) but the regens are based on a set profile not build up. Drive X miles, it regens. Running perfect fuel would not change the number of regens, but IT WILL extend the life of the filter and all components involved.
Never shut down during a regen, the heat build up is an issue long term (life cycles) and it wastes more fuel doing the regen all over again later. Try to run a gauge showing EGT (easily done from OBD info) and run around the block again or leave it idling to finish and let it cool down to 300-400F before shutting off.
I have noticed the VW common rails develop a lot more engine noise at 70-100k miles with most owners, I am guessing it is injector wear. They get really sick sounding beyond that and it is a slow change so most do not notice. It is crazy how quiet a brand new one is versus what they become.
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