Bio-diesel won't hurt older engines - here's a link to some products for added lubrication http://inchoate.harm.org/~halbritt/dodge/Diesel%20Fuel%20Additive%20V3.pdf   I have used 25% blend (when bean oil was cheaper then diesel) in a '69 model 1256 IH with no problems. In fact, it didn't smoke as much. I've read and heard of irrigation guys useing 100% bean oil (again when it was way less expensive then diesel) on old irrigation motors with no problem. Today, bean oil is quit a bit more then diesel. Last load of farm diesel, my supplier indicated, Minnesota's mandated 2% blend was adding about 4¢ gal to the price of farm diesel.

Are you using soybean oil or vegtable oil from resturants? or maybe canola oil?