John Oldner drives his diesel truck daily, but he hasn't stopped at a commercial service station in more than a year.

He powers his pickup with used cooking oil that is processed into biodiesel fuel. He pays $2.55 a gallon – about half what others shell out for diesel.

Mr. Oldner, a Murphy lawyer, briefly concocted backyard biodiesel with leftover oil from Bill Smith's Cafe in McKinney. He pumped the thick substance through two household water filters to remove food particles and added an anti-gelling agent.

"It's a very messy process," said Mr. Oldner, 71.

Now he buys from a secret source in an adjacent county. The biodiesel maker has all the word-of-mouth business he can handle and wants no publicity.

Mr. Oldner, father of state District Judge Chris Oldner, thoroughly researched biodiesel before putting cooking oil into his 2005 Dodge truck. He didn't listen to naysayers.

"Nobody's critical of it now," he said. "Everybody admires me."

Turns out, some people have been running diesel engines on vegetable oil – only slightly processed – for decades.

But the biodiesel bandwagon is getting crowded with regular diesel approaching $5 a gallon. Companies sell a host of products to help the do-it-yourself who wants to kick Big Oil in the shin.

"Make your own biodiesel," screams one Web site.

"You'll love the savings," says another.

Mr. Oldner injects a word of caution. Yes, most people could make limited amounts of biodiesel. But the process is time-consuming and involves some trial and error.

For instance, cooking oil can clog fuel filters if it isn't properly thinned, he said.

Still, Mr. Oldner has no regrets about his foray into fuel production and wants others to join in.

"We owe it to our fellow diesel guys to convince them they should do this," he said. "There is no single answer to our energy problems. But there are answers."

Mr. Oldner has traveled a long and winding career path. After earning a bachelor's degree in mathematics from Texas Western College in 1964, he maintained large military computer systems, owned a wrecking yard that specialized in Volvo parts, and developed a Murphy subdivision.

He started law school when he was 55. He graduated from Texas Wesleyan University at age 59 and now practices family law out of his home.

In his spare time, he plays guitar in a country-Western band.

"I'm always doing something," Mr. Oldner said.

Judy Oldner, his wife of 46 years, wasn't surprised when her husband ventured into homemade biodiesel.

"As usual, he was ahead of the game," Ms. Oldner said. "I don't want to get into it. But if it makes him happy, go for it."

Bill Smith Jr., the McKinney cafe owner, gladly gave Mr. Oldner his kitchen oil that had cooked French fries and chicken-fried steak. Mr. Smith poured it into 5-gallon jugs for Mr. Oldner to pick up.

"I had a company that was buying the oil," Mr. Smith said. "But since he's a local guy, I thought it would be nice to let him have it."

One slight downside to biodiesel: the smell. The exhaust fumes have a peculiar odor.

"Like stale cooking oil," Mr. Oldner said, laughing. "It only lingers for a few seconds after you start it up. Some people find it offensive. Personally, I don't."