Quote:
Originally Posted by fshagan
All diesels can run on bio-diesel ...
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Note: my reply below is part speculation, part observing tdiclub posts and reading between the lines. Once we get through another summer here in N.A. I think we'll know the biodiesel limitations of the 2009 tdis much more clearly.
While the fuel system in the 2009 TDIs can certainly handle biodiesel, and it will burn in the cylinder exactly as regular diesel, it still appears unwise to run pure bio in these VWs. The issue lies with the ECU controlled diesel particulate filter regeneration (DPF) period. When running regular diesel, soot will accumulate slowly in the DPF. After so many hours or miles of engine operation, the ECU triggers a special fueling strategy that basically dumps unburned fuel into the exhaust. The fuel collects in the DPF and raises the temperature high enough to burn off all accumulated soot. Basically a well controlled high temperature incineration of the soot, quite clean burning.
Unfortunately, with pure biodiesel, the DPF temperature during this regeneration period does not get hot enough to satisfy the value the ECU expects to see from the thermocouple mounted in the DPF. Apparently, anyway. This is not actually a problem whatsoever, but it triggers a fault code in the ECU. Biodiesel actually burns much cleaner with far less particulates than regular diesel, so potentially it will never clog up the DPF anyway. One other concern with bio is that when it dilutes the engine oil, it is far more detrimental to engine lubrication than regular diesel is. Supposedly. The fueling during DPF regeneration comes a post injection event (well after main injection) and thus washes the cylinder bores and ends up diluting the oil somewhat. However I havent seen any proof of danger from biodiesel here.
For what its worth, VW only approved B5 in ALL the earlier model TDIs also. My 2003 ALH TDI runs like its made for pure bio... I hate using reg. in the winter. I have my fingers crossed that the 09s can at least run a B50 mix safely.