first rule of repair:

When it comes to biodiesel performance, one single issue causes more heartache than any other for new B100 users. It's the clogged fuel filter.

A friend recently came to visit on a mild Autumn day, driving his recently-purchased 1995 Chevy 2500 pickup truck. After a few hours visit he got back in the truck to drive home, only to find that it wouldn't start. It cranked and cranked. "Usually it takes a while," he said, as he grabbed a can of starting fluid to spray in the air filter, "ever since I started it on biodiesel a couple of tanks ago. I think I made a bad batch."

Another B100 user nearly stymied a VW repair specialist in Maryland recently. A mechanic started up the TDI Golf he'd left in the lot overnight to take it on a test drive. A half mile from the shop, it shut off and coasted to a stop.

I want to repeat some advice here that Dr. Dan Freeman, of Dr. Dan's Alternative Fuel Werks, gives his biodiesel-guzzling customers when they run into engine problems.

At the first sign of trouble, before you do any other diagnosis, change your fuel filter.

Seriously. Your fuel filter!

We got the Chevy truck started, drove down to the auto parts store, and voila, the replacement fuel filter solved the problem.

The Golf's fuel was ASTM, but made from high-cloud-point animal fat. The morning was just too chilly. The wise mechanic took the fuel line off the cold filter, dropped it directly into a quart bottle of automatic transmission fluid, and drove it easily back to the shop to warm the whole car up inside a heated bay. Once the filter was warm, the fuel didn't gel and the clog was gone.

If your truck, tractor, or TDI is struggling, chances are your fuel quality is fine. Save yourself from an evening of dubious advice from armchair diagnosticians in the online forums. Just change your fuel filter.