Welcome to the forum!

Biodiesel has high solvent properties. That is, it dissolves petrodiesel deposits. It also has a solvent effect on fuel lines made of natural rubber.

This does two things:

1) It cleans out the tank and fuel lines of deposits from petrodiesel.
2) It causes natural rubber fuel lines to become soft and to weep.

It also tends to clean out injectors and injector pumps, so in many ways it is a good thing there.

In order to run biodiesel long-term, you need to take into account that over time the natural rubber components that come in contact with the biodiesel will need to be replaced.

Also, as the biodiesel dissolves the deposits from the tank and the lines these deposits will tend to be caught in the fuel filters. You need to stay with a fairly low percentage of biodiesel to avoid the solvent effect from being too great and just plugging things too quickly (B20 is a good starting point in my opinion). Monitor your filters, and carry spares (plus tools).

As you go through tankfuls of biodiesel/petrodiesel blended fuel, you can slowly start ramping up the percentage. I started with B20, then went B50, B75, and now finally B100 over 4 tankfuls. I did have to swap filters once. It appears that my lines and tank were pretty clean, some people need to change out filters 3-4 times as they ramp up.

On the fuel lines, if your lines are new or newer (i.e. in good shape, not mushy or soft) then you will be OK for several months. It's not like biodiesel simply dissolves the lines. It simply makes them mushy over time - if you have new rubber lines, it can take months or more than a year. For most W123s, there are 3 lines in the engine bay to be swapped out, and three lines back above the rear axle coming to/from the fuel tank. On the W123, the only tricky one is the main fuel line coming from the tank. This one has a proprietary screw-in connector that needs to be replaced. The factory part has a natural rubber line crimped to a screw-in connector that goes to the tank. Most people use a hacksaw and cut the connector off, and then use a hose clamp to put a newer type fuel line on. All other connections are with regular hose clamps (and I HIGHLY recommend the european clamps, rather than the nasty screw type US clamps).

You can swap them out for newer fuel line which is more resistant to biodiesel. All fuel lines will eventually degrade and leak, it is simply that the older natural rubber lines do it a lot more quickly.

Biodiesel has a higher cetane rating, but it's overall BTU/gallon is lower than petro-diesel. Therefore it's not too surprising that you will get a few miles per gallon.

Sincerely,

PE

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83 240D - 4 speed manual - Manilla Beige
189K miles, Tachometer mod, cool wooden shift knob from PeachParts, CocoMats, Original factory paint, manual windows, manual sunroof. Starting to add AudioWrap to this car too!

Biodiesel has about 6% less energy (BTUs). As WK has only replaced 20% of his fuel with biodiesel, I doubt if there will be a measurable difference in mpg.

Perhaps you should try 4 tank fulls to get a more accurate reading.

Oh, and since you asked, Yes you are missing something.

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1987 300TD 309, xxx 2.8.2014 10,000 mile OCI


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