Hello. I am wondering what fuel I should put in my 85' 300D. Now with the new Ultra-Low Sulfur Diesel my car is slowly leaking fuel. I want to put some other fuel such as Biodiesel but I don't know if it can handle temperatures as low as 0 degrees F. What do you suggest?
it all depends on what type of biodiesel you choose to use, there are many types, b5 through b100, b100 being 100% biodiesel, if it gets that cold where you live, its probably not a good idea, try the lowest amount of biodiesel, and keep increasing it, but I probably wouldn't go to high, you'd probably still want to dump some anti-gelling agents, and or diesel
And as for using veggie, the same applies, I would use a booster pump prior to your IP, then maybe even some injection line heaters, nice and hot before you start-up, but even with that, I wouldn't go more then 10-20% veggie (rest being diesel)
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'84 300DT 314k (w123);
'80 300SD (w116), two-tank fuel system
Actually, high sulfur diesel has something in it which makes all the seals in the line swell up. ULSD doesn't have this, and it leaches out the product making the seals smaller again. If the seals are in good condition, then they will simply go back to normal size. However, like many diesels that are 25 years old such as the 300D, the seals are worn out and aged. If I am correct, adding a mixture of biodiesel will fix the problem. But then it will gel in the cold weather.
Actually, high sulfur diesel has something in it which makes all the seals in the line swell up. ULSD doesn't have this, and it leaches out the product making the seals smaller again.
You are incorrect. Even if ULSD did cause seals to shrink, your 300D has no seals for the fuel to affect because your engine has copper crush washers. Only the 84+ OM60x engines have o-rings that could be affected.
People like to blame ULSD for leaks because it is a convenient excuse. Fact is, if it leaks, it was most likely going to do so no matter the fuel used. Rubber does not last forever and through the thousands of heating and cooling cycles it will eventually cause it to fail.
Then why did it start leaking only after I put it in? I've had this car for years and never had this problem before. Anyways, here is where I got the info from:
"Diesel fuel systems contain "O-rings" and other parts made of elastomeric materials. These elastomers swell slightly when they contact diesel fuel, because they absorb aromatic compounds from the fuel. Exposure to a fuel with a lower aromatics content will result in some of the absorbed aromatics being leached out, causing the elastomer to shrink towards its original size. If the elastomer is still pliable, this shrinkage will not cause a leak. However, if age or service at higher-than-normal temperatures has caused the elastomer to loose its elasticity, a leak could occur. Vehicle owners should be aware that elastomeric parts have finite lives and should be replaced as necessary.
By itself, low sulfur or low aromatics diesel fuel does not cause fuel system leaks. They are caused by the combination of a change from higher to lower aromatics fuel and aged O-rings and elastomeric parts that have lost their elasticity."
Biodiesel & SVO in cold weather? 
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