It really sounds too good to be true, running a diesel on used vegetable oil. Not to be confused with biodiesel fuel blends, which actually have only a small percentage of vegetable oil, we're talking about burning straight veggie oil in your engine instead of diesel, which a growing number of diesel owners are already doing. Here's the basic approach: First, you just siphon some cooking oil from a deep-fat fryer at your local restaurant, filter out any debris, and pour it into a secondary tank in your vehicle. Next, after starting up your vehicle on diesel fuel and getting the engine up to operating temperature, and also warming the veggie oil with a heat exchanger in the tank, you flip a switch that transfers over to the vegetable oil system.
Joel Woolf of Veg Powered Systems pours filtered vegetable oil into an auxiliary tank of his Dodge Ram.
Then, you simply drive down the road free of charge. That's right: zip, nada, nothing-no price gouging at the fuel pump. Restaurant owners are thrilled to see you empty their barrels, since they otherwise have to pay to have it hauled away. Or you can run on unused, food-grade oil, either fresh or rancid, which in bulk form actually costs less than diesel at the pump and requires no filtration. Not only that, by running on used vegetable oil, you're putting a waste product to good use, since a gazillion gallons or so need to be disposed of every year. Moreover, you'd be doing your part to reduce our country's dependence on foreign sources of petroleum. As for performance, your engine actually runs cleaner and quieter on veggie oil, reducing harmful pollutants, with no loss of acceleration or mileage.
Paul Powers' Chevy C4500 Kodiak, outfitted with a utility bed and camper top, runs regularly on vegetable oil and tows a trailer as well. | 
Joel Woolf's late-model Dodge Ram has a common-rail fuel system and runs smoothly on vegetable oil. | 
Here are details of the system in the Chevy C4500: filter, pump, and water separator. |
So, what's not to like? Good question, one that we had to answer. That meant doing a bit of digging and getting our hands greasy. A number of companies offer vegetable-oil fuel systems-check Google for grease conversions. While similar in concept, they differ in design, and as with any new technology, it's a caveat emptor situation. So, do your homework before you start filling up buckets in your garage from your local Taco Bell, and stay tuned to Diesel Power for future features on this subject.
There is a separate gauge for the vegetable oil tank.
For this first article, we focused on one firm in particular, Veg Powered Systems, based in Ojai, California. We chose to start with this one partly because its owner Joel Woolf is a diesel mechanic with more than 20 years of experience, so we figured he knows his way around an oil-burner. Also, we were able to drive a couple of his converted vehicles (a Dodge Ram and a Mercedes sedan), and met a customer who has driven extensively with a Veg Power system on his Duramax-powered Chevy C4500 Kodiak truck.Looking at the concept in general, it's entirely plausible to run a diesel on veggie oil. After all, Rudolph Diesel originally designed his invention to run on peanut oil. The main problem is that vegetable oil is much more viscous than conventional diesel fuel, which means that before attempting to spray vegetable oil through your engine's injectors, it must be heated (thinned) in order to be properly atomized. In addition, the engine should be up to operating temperature before running on vegetable oil.
Just flip the toggle switch on the dash to switch from diesel to vegetable oil, or back again.
If both of these conditions aren't met, the vegetable oil won't burn properly, forming deposits on the injectors and in the cylinder head, leading to poor performance, higher emissions, and reduced engine life. To overcome these problems, the approach is to create a heated auxiliary fuel system that is activated once the proper operating temperature has been achieved.
In Woolf's Veg Powered Systems, the vegetable oil never enters the stock diesel fuel filter and is never pumped by the stock electric fuel pump. For a price of less than $2,000, the system's components consist of separate pumps, filters, fuel gauge, switch, solenoid, valves, fuel line, and an insulated 50-gallon tank to hold the vegetable oil. Mounted inside the tank is a heat exchanger made from coils of copper tubing adjacent to or surrounding a perforated pick-up tube for the vegetable fuel-oil line. Hot fluid from the engine's coolant system runs through the tubing to bring the vegetable oil up to temperature, usually in just a few minutes. Woolf points to the engine's factory water temperature gauge as a guide as to when to switch over to vegetable oil. The magic number here is 160 degrees F-anything less and you're asking for trouble.