The only negatives with BioD are the following:** assuming B100
Slightly less fuel mileage (less than 10% difference)
Eventually your fuel hoses will need replacing if original
Initially, you will have to change the fuel filter earlier than normal (this will go back to normal after several thousand miles)
In colder weather (sub freezing), you will need a blend because some BioD will gell much quicker than #2

On the other hand, your fuel system will be much cleaner, you will have less noticeable smoke, it usually quietens the engine, and it should run smoother.

I make and run BioD most all the time.

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87 300SDL - 215K Miles !!
99 F-350CC Dually PSD - 190K
86 300SDL - 189K
All on B-100