Author Topic: Biodiesel  (Read 3295 times)


  • 5 O'Clock Shadow
  • *
  • Posts: 90
« on: February 07, 2014, 02:12:59 PM »
I have a 2010 Jetta TDI. I was considering using biodiesel and think I found a gas station fairly convenient for me that sells it. Since I know very little about vehicles in general especially specifics about diesels I wanted opinions. Is there anything I should know about using biodiesel? If I start using it do I need to keep using it regularly? Does it affect fuel mileage?


  • Pencil Stache
  • ****
  • Posts: 538
Re: Biodiesel
« Reply #1 on: February 07, 2014, 09:12:25 PM »
Research well before you make a decision:

I think most of those horror stories come from the home-cooked variety but even the dealerships warn you away from most everything but the commerical B5.


  • Handlebar Stache
  • *****
  • Posts: 1117
Re: Biodiesel
« Reply #2 on: February 07, 2014, 09:35:36 PM »
From what I understand, the problem with homecooked biodiesel is generally the inability to totally filter particulate matter, and completely remove water.   I'm not sure about the commercial stuff.

Be careful with a tdi, parts are ridiculously expensive when they break.   How much is that high pressure fuel pump going for these days?


  • Magnum Stache
  • ******
  • Posts: 4725
  • Location: Atlanta, GA
Re: Biodiesel
« Reply #3 on: February 07, 2014, 11:03:22 PM »
Note: I own a 1998 TDI, and am active on

First of all, do not trust anything anyone at a VW dealer says. The TDIClub forums (and I'm sure the forums too) are full of horror stories about dealers screwing up people's TDIs. even has a sticky in the TDI 101 section titled "Newbies: do not take your car to the dealer!" or something like that.

Second, biodiesel is great, but you really do want commercially-produced biodiesel that has been tested to comply with the ASTM D6751 standard. If you have an old Merc or old pickup truck homebrew all you want; they'll run on anything. VW TDIs, on the other hand, are pickier. If you are very, very sure about your technique -- you know that you've properly removed all the glycerin and all the water -- then you might have success with homebrew, but it's more of a risk.

Third, your car is too new and should not use biodiesel (more than 5%) for three reasons:
  • The high pressures in the common-rail injection system might cause the biodiesel to gum up in it and/or make it wear out more quickly. This includes the high pressure fuel pump (HPFP), which has been known to break and spread metal particles throughout the injection system and engine and require complete replacement, which is $10,000 (dealer prices).
  • The reason it's a "clean diesel" is that it has a diesel particulate filter (DPF), and the engine goes through "regeneration cycles" periodically to burn off the accumulated soot. This involves injecting extra fuel at the end of the combustion event, which increases exhaust gas temperature (EGT). Because biodiesel fails to burn in this case the cycle doesn't work correctly, and the DPF plugs up and fails.
  • Also because the post-injected diesel fails to burn, it washes down the cylinder walls, past the piston rings, and contaminates the engine oil leading to accelerated engine wear.

Now, all three of these issues might be able to be mitigated:
  • It might be the case that Bosch was overly-conservative in their estimate of how well biodiesel could work in the injection system. The HPFP failures might have been the result of manufacturing or design defects, and not actually be more likely when using biodiesel.
  • If there weren't a DPF, then there'd be no concern about it failing. Unfortunately, as part of the emissions system, it's illegal to remove. Ironically, if the engine were tuned to use biodiesel instead of dino-diesel then it would run clean enough not to need the DPF in the first place!
  • The oil-contamination issue happens over time; there are those who believe it can be mitigated by simply using a shorter oil change interval.

My recommendation would be to sell your 2010 and replace it with a 2002-2003, which has the same "ALH" motor as my 1998 and runs B100 without any problems. Get one with a manual transmission; the automatics fail often. (Or, if a 2003 is too old for you -- and it shouldn't be -- then a 2004-2006 with a "BEW" motor is almost as good. If you go that route, beware cam wear.) As a bonus, your fuel economy should go up about 10 mpg compared to your 2010. Also, get a tune (and, if ALH, larger injector nozzles) and you'll be just as fast as your 2010, while keeping the better fuel economy.

If you insist on running high-percentage blends of biodiesel in your 2010, I recommend you cut your oil change interval to 5000 miles (but still use oil that meets VW's 507.00 specification!!!), talk to a tuner about getting a biodiesel-specific ECU mapping, and live in a state that doesn't do emissions testing on diesels.


  • 5 O'Clock Shadow
  • *
  • Posts: 90
Re: Biodiesel
« Reply #4 on: February 08, 2014, 10:36:08 AM »
Thanks for the info. After looking further I don't think I can even get biodiesel near me anymore anyway (maybe could have 6 years ago...). I've heard about and really need to check it out...I've only had it since July so I haven't had anything besides very basic maintenance done to it so far

As for my particular car, I love my TDI and it fits all my needs. I can't really go with an older one since they always have a ton of miles on them already and I (unfortunately) am a car clown for another couple of years and put ~25k miles on my car a year (non-negotiable for now since I will not move my 13 year old Great Dane again). As for the fuel mileage on it; I get much better than it's rated. Even now with it being low due to subzero temperatures I'm averaging 38mpg. In the summer it was mid-to-upper 40's and could even get 50mpg if I really babied it.