Green Transportation Basics: Vegetable Oil Conversion

Diesel Engines and Diesel Fuel  

The diesel engine got its start in the 1870s, thanks to the pioneering work of Rudolf Diesel, a bright young engineering student attending the Polytechnic High School of Germany (the equivalent of an engineering college). After learning how inefficient conventional engines were, Diesel decided to design and build a more efficient one. In 1892, after years of work, Rudolf Diesel obtained a patent for the engine that now bears his name.

Although it was considered a breakthrough in engine technology, Diesel’s invention was pretty similar to conventional gasoline engines in many respects. For example, the diesel engine is still a two- or four-stroke internal combustion engine. Like its predecessor, the diesel engine transforms chemical energy in the molecules of the fuel into mechanical energy. As with engines in conventional vehicles, combustion of the fuel inside the cylinders creates a series of small explosions that drives the pistons. The pistons, in turn, are connected to a crankshaft. The up-and-down motion of the pistons creates a rotary motion that turns the wheels propelling the vehicle forward. (You can view an animation of a four-stroke diesel engine online.)

Although diesel engines are similar to gasoline-powered internal combustion engines, there are some significant differences. One important difference is the way in which the fuel is ignited inside the cylinders. In a gasoline engine, as noted in the sidebar, the fuel is mixed with air and drawn into the cylinder during the intake stroke — when the piston descends. The piston then rises during the compression stroke. The compressed air-gas mixture is ignited by a carefully timed electrical spark generated by the spark plugs that project into each cylinder. In a diesel engine, fuel is injected near the top of the compression stroke as the piston reaches the top of the cylinder. Ignition is not initiated by a spark, either. In a diesel engine, it is triggered by heat generated by the compression of air in the cylinder during the compression stroke. (Air heats up when it is compressed.) The explosion caused by ignition of the fuel forces the cylinder down. 

Another very important difference between diesel engines and gasoline engines is the way fuel is mixed and injected into the cylinders. In older gas-powered cars, vaporized fuel is mixed with air in the carburetor located on top of the engine. The gas-air mixture is then delivered to the cylinders during the intake stroke. In newer vehicles equipped with fuel injectors, air and fuel are mixed outside the cylinders and are then injected into each cylinder. The air-fuel mix is injected into the cylinder during the intake stroke. 

In diesel engines, fuel is injected as a fine mist either directly into the cylinders or into pre-combustion chambers, then into the cylinders. The fuel is not mixed with air prior to injection. Those diesel engines in which fuel is injected directly into the cylinders are known as direct injection (DI) engines. The injector sprays the fuel into the cylinders as a fine mist so that it ignites efficiently. 

In an effort to ensure that fuel is evenly distributed in the cylinder, some diesel engines are equipped with pre-combustion chambers (also called swirl chambers), as mentioned above. Fuel is introduced into the pre-combustion chamber, and then is injected into cylinders as a fine mist. This helps facilitate combustion and boost efficiency. Engines equipped with such devices are known as indirect injection (IDI) diesel engines. To facilitate starting in cold weather, some diesel engines are equipped with glow plugs. Glow plugs are wires located in each cylinder. They carry electrical current from the batteries each time a diesel engine is started. The flow of electricity through the wires creates heat that warms the inside of the cylinders — in the same way that electricity flowing through the elements of an electric stove or light bulb creates heat. The additional heat aids the ignition by compression when a diesel vehicle cold starts. Preheating the combustion chamber does require some time, usually 10-20 seconds, during which time the driver must sit idly by. Without glow plugs, compression may not increase the temperature of the compressed air sufficiently during cold weather. 

Smaller engines like those of diesel lawn tractors and many older diesel car engines typically come with glow plugs to aid in cold-weather starting. However, newer vehicles and larger engines contain advanced computer controls that eliminate the need for glow plugs. These vehicles have sensors that measure ambient air temperature. If it is cold, a signal is sent to the onboard computer. It retards the timing of the engine (when the fuel is injected into the cylinders). As a result, the injector sprays the fuel into the cylinder at a slightly later time during the compression cycle. Because the air is more compressed later in the cycle, it is hotter. This, in turn, allows cold starting without glow plugs. Diesel cars, trucks, and tractors have historically been powered by diesel fuel, a mixture of hydrocarbons extracted from crude oil (petroleum). Crude oil was formed deep beneath the Earth’s surface from ancient marine algae.  

Diesel is an oily fuel, much heavier than gasoline. The carbon compounds in gasoline have an average of about nine carbons each, while those in diesel fuel have 14. Because the molecules are longer, there are more chemical bonds to break. Chemical bonds store energy. So the more bonds, the more energy an engine can extract from a gallon of fuel. In fact, one gallon of gasoline contains 125,000 BTUs (132 by 106 joules). A gallon of diesel fuel contains approximately 147,000 BTUs (155 by 106 joules) — that’s about 19 percent more energy per gallon. The higher energy density of diesel fuel and its higher engine efficiency are the two main reasons why diesel cars and trucks get better mileage than their gasoline-engine brethren. 

Converting a Diesel Vehicle to Run on Straight Vegetable Oil 

Vegetable oil can be burned in a diesel engine, but as pointed out earlier, to do so, you — or a qualified diesel mechanic — must first install a conversion kit. If you just fill your tank with vegetable oil and then head out for work, you’ll be sorry. Conversation kits come in two varieties: single-tank and two-tank. As you shall soon see, they contain many of the same components. A high-quality conversion kit will run you about $1,300 to $2,000. If you hire a diesel mechanic to perform the work, add another $600 to $800. 

Both types of kits contain components that heat the vegetable oil. Heating the fuel is necessary because veggie oil is about 10-17 times thicker (more viscous) than diesel fuel. Raising its temperature reduces its viscosity (thickness) so it can flow effortlessly from the fuel tank through the fuel line and the fuel filter and then into the fuel injectors, even on cold days. Heating veggie oil reduces the work the fuel pump must do to move the oil from the fuel tank to the engine. If the oil’s too thick, the pump may not be able to deliver a sufficient amount of fuel to the engine, starving it of fuel. Even if the pump is strong enough to move the oil, higher pressure or a vacuum in the system could cause problems elsewhere. It could, for instance, cause fuel lines to rupture or fittings (connections) to leak. If thick oil makes it to the injectors, its high viscosity will result in a spray that evaporates slowly and unevenly. “The uneven spray leads to incomplete combustion and liquid oil hitting the cylinder walls,” notes Forest Gregg, author of SVO: Powering Your Vehicle with Straight Vegetable Oil. This causes carbon deposits on various components, which results in numerous problems that reduce engine efficiency, create more wear and tear, and shorten engine life. (I’ll explore this topic shortly.) Single- and two-tank diesel conversion kits contain other components as well, including automatic or manual controls, valves, and meters, which will be described in more detail below. 

Two-Tank Conversion Kits 

Two-tank conversion kits are widely used in North America and Europe. As their name implies, they require two tanks, the stock tank, which is filled with diesel, and an additional tank for the vegetable oil. The second tank is usually installed in the trunk of a car or the bed of a pickup truck. 

Two-tank kits come with a fuel tank heater, fuel line heater, and fuel filter heater. Collectively, they raise and maintain the temperature of the vegetable oil over 160 degrees Fahrenheit. The fuel tank heater is typically a coiled aluminum or copper pipe. (Copper should be avoided as it is a catalyst that causes vegetable oil to react chemically, producing unfavorable byproducts.) According to the leading manufacturer of conversion kits, Frybrid, most kits include only a small heat exchanger in the veggie oil tank to heat the fuel to injection temperature (160 degrees Fahrenheit). Their system utilizes four heat exchangers to “assure that all fuel being drawn from the tank is liquefied,” according to the company’s website. This “lessens the strain on the injection pump and/or fuel pump.” 

To convert a car to run on vegetable oil with a two-tank system, you must first install the additional tank for the vegetable oil. You must then tap into the vehicle’s liquid cooling system to heat the diesel in the tank, the fuel line, and the fuel filter. This is done by installing a tee fitting on the hose that runs from the engine to the cabin heater core. (The heater core is the heat exchanger from which heat is withdrawn on cold winter days when a car’s heater is on. It is located just behind the engine compartment, behind the firewall.) 

Valves and switches must also be installed. For example, a solenoid valve needs to be installed to allow the driver to change between fuel tanks. The kit should also contain a flushing valve that will clear the vegetable oil from the fuel line before the engine is turned off. Both valves are controlled by dash-mounted switches. 

The valves and switches allow the driver to begin and end trips on petro-diesel. Ending a trip on petro-diesel ensures that all the vegetable oil has been purged from the fuel lines, pumps, and fuel filter. This prevents the system from getting clogged by vegetable oil that solidifies on cold days. A two-tank kit contains a fuel gauge for the vegetable oil tank. It also comes with hoses and connectors. They are required to circulate hot engine coolant to the fuel lines, the fuel filter and the fuel tank, keeping the fuel hot from the tank to the engine. 

When a car fitted with a two-tank system is operating, engine coolant flows from the tee fitting (mentioned above) via a one-inch radiator hose. It forms a hot coolant jacket surrounding the fuel line that carries vegetable oil to the engine. 

This hose also carries hot engine coolant to a copper coil that surrounds the veggie oil filter (some vehicles have electric fuel filter heaters). The coolant then proceeds to the vegetable oil tank where it flows through the heat exchanger(s). The coolant is then returned to the engine by yet another hose where it is reheated. 

Operating a Two-Tank Car on Straight Vegetable Oil 

Now that you understand how the system’s set up, let’s look at how one drives a veggie oil car with a two-tank kit. When operating a vehicle on straight vegetable oil, the driver must cold-start the vehicle on either the diesel or biodiesel stored in the stock tank. Once the engine and the vegetable oil are warmed up, however, the driver can switch the vehicle to SVO. This usually occurs 5 to 15 minutes after starting the engine. The car then runs on straight SVO. Before the engine is shut down, however, the driver must switch from veggie oil back to diesel or biodiesel. The vegetable oil in the fuel lines is then purged by diesel fuel from the stock tank. The unused vegetable oil purged from the lines flows back into the veggie oil tank. 

Purging of the fuel lines should occur as a driver approaches his or her final destination. This process ensures that the vehicle is ready for its next cold start — that is, that there’s diesel in the fuel line when the car is started again, not vegetable oil. As noted previously, vegetable oil can solidify in cold weather. Even if it doesn’t, cold vegetable oil injected into the cylinders does not burn as efficiently if its viscosity is too high. This leads to coking (carbon deposits) and other problems. Switching can be controlled manually or by an onboard computer, like the Co-Pilot Computer Controller. This device takes the guesswork out of running on vegetable oil. The Co-Pilot not only simplifies operation, it keeps drivers from making the most common switching mistakes: converting to vegetable oil operation too quickly and forgetting to switch back to diesel near the end of each trip. 

The Co-Pilot’s LCD screen displays operation temperatures and notifies the driver with an audible signal when the proper engine temperature is reached so the driver knows when to switch to SVO. In the auto mode, the Co-Pilot automatically switches the vehicle to vegetable oil at the right time. A timed purge function in this and similar controls activates an automatic back-flush that turns on when the engine is switched off. This eliminates the need to switch back to diesel or biodiesel five minutes before shutdown. It also eliminates the possibility of over purging, which results in diesel or biodiesel contamination of the veggie oil. 

Two-tank kits are better for longer-distance driving than for short stop-and-start trips. If you use your car principally to run to the grocery store ten minutes from your home, a two-tank kit will provide very little, if any, advantage. You’ll be running on petro-diesel most of the time. Running your car on biodiesel or installing a single-tank system would be a better choice. 

Single-Tank Conversion Kits 

Single-tank conversion kits are the simplest kits on the market, though less commonly used in North America. Single-tank kits employ the vehicle’s stock fuel tank to store vegetable oil. No other tank is required. Vehicles run on 100 percent straight vegetable oil 100 percent of the time, except perhaps in cold months. A car equipped with a single-tank system therefore starts and stops on SVO — just as if it were diesel or biodiesel. Single-tank kits were developed in Germany and are extremely popular in Europe. Reportedly, cars equipped with single-tank systems can operate on 100 percent straight vegetable oil at ambient temperatures as low as 14 degrees Fahrenheit. When temperatures drop below 14 degrees Fahrenheit, the vehicles can be run on winterized diesel or biodiesel. Winterized diesel is diesel fuel with an additive that prevents gelling in cold weather. Supplementary fuel heating is also available for operation on SVO in really cold areas. Single-tank systems are made by three German companies: Elsbett, VWP and Wolf Pflanzenöltechnik. The folks at journeytoforever.org, who are unabashed proponents of single-tank systems, claim that these kits are suitable for both direct and indirect injection diesel engines. Other sources suggest that they’re not well suited for direct injection engines. When you’re starting a DI engine, they argue, the engine and fuel may be too cool to achieve complete combustion, which can lead to serious problems (discussed shortly). 

Direct injection engines equipped with electric block heaters may be an exception. Block heaters keep engines warm when a car is switched off in cold weather, so the engine will be warm enough for starting to achieve efficient combustion. So, if you are considering a single-tank kit, do your research. Talk to people who have experience with conversions. Remember, the main goal in all SVO systems is to reduce inefficient combustion, especially when a vehicle is first started. If the vegetable oil and engine are not sufficiently heated at this time, the result could be a poor spray pattern when the fuel is injected into the cylinder of a direct injection engine. A poor spray pattern results in inefficient combustion that leads to the formation of carbon deposits in the injectors. Carbon deposits on the injectors can also cause the injector needles to stick. (They control the amount of fuel entering the cylinders.) Sticking, in turn, can result in too much or too little fuel being injected into the engine — depending on where the injector is stuck. If too much fuel is delivered, the car produces more pollution. If too little fuel is injected, the vehicle will be underpowered. Carbon deposits also form on intake and exhaust valves and the exhaust valve stem. Carbon deposits gum up the works, make the engine work harder, and reduce efficiency. Because the fuel burns less efficiently, the car produces more air pollution. Yet another problem caused by incomplete combustion is that unburned vegetable oil can seep past the rings on the cylinders and drip into the crankcase oil during start-up. This contaminates the engine oil. The rings encircle the pistons and ensure a tight fit in the cylinder so fuel does not leak into the crankcase oil and vice versa. Upon starting, there’s a small gap between the piston and the cylinder wall when the engine is cold. This gap may allow vegetable oil to leak into the engine oil. As the engine warms up, the pistons expand, closing this gap. Vegetable oil in the crankcase oil is a problem because it reduces the efficiency of the engine and increases wear and tear on engine parts, reducing the life of a vehicle. 

Practical Considerations 

SVO conversion kits can be installed by an individual with minimal mechanical abilities with tools commonly used by mechanics. If you are not at all mechanically inclined, however, you may want to hire a professional mechanic; better yet, one who has performed SVO conversions before. Call around to local diesel mechanics for references. 

While nearly any diesel engine can be converted to operate on vegetable oil, there are some exceptions. It’s a good idea, for instance, to avoid vehicles with rubber seals because vegetable oil dissolves rubber (rubber and veggie oil are chemically similar and, in chemistry, like dissolves like). Many older diesels were equipped with rubber seals. 

Certain types of diesel engines are also better suited to run on pure vegetable oil than others. Mechanical injection is better than computerized injection, and indirect injection is generally better than direct injection, except perhaps for VW TDIs. Unfortunately, all newer diesel engines come with direct injection engines. 

Be sure to look into the type of injector pump, too. Some are better than others when it comes to SVO operation. To ensure the engine lasts, you’ll need to change the oil more often than you’re probably used to. Bear in mind, too, that certain vegetable oils work better than others. Mustard and canola oil are among the best because they are high lubricity (low viscosity) oils. In colder climates, use canola, soy, sunflower or corn oil because they don’t solidify as quickly as other types of oil. 

For reviews of both single- and dual-tank vegetable oil conversion kits, visit FUSEL.com. The site also contains information on ways to obtain designs so you can fabricate your own conversion components from common off-the-shelf hardware, plumbing, and auto parts. Remember, though, that most experts recommend buying a kit rather than going this route. 

Securing a Supply of Vegetable Oil 

Before you decide to convert your diesel to SVO, be sure you have a reliable supply of vegetable oil. Some individuals purchase refined vegetable oil (unused vegetable oil) in 5-gallon containers or, more commonly, 55-gallon drums. To cut costs, you may want to join with other greasers and buy veggie oil in bulk. Unused vegetable oil costs about the same as petro-diesel when purchased in bulk. 

A much cheaper option is to secure a source of used vegetable oil. Many restaurants will gladly donate their waste oil and even the containers to carry it away in. Chinese and Japanese restaurants are usually considered the best source because their oils are the cleanest. They are used only once to cook, then discarded. 

Oil from other restaurants may be suitable but will likely require more effort on your part to make it usable; mostly, this involves removing food particles. Most restaurants use their deep fryer oil to cook many different foods, bits of which end up in the oil. It’s fairly easy to remove the larger bits and pieces by settling or settling and filtration. Flour from breading, however, forms a murky gravy-like suspension in the oil that can be quite difficult to remove. Also, be aware that oil from restaurants that deep-fry meat may contain water, which can seriously damage an engine. Such oil also typically contains animal fat. Animal fats solidify at higher temperatures than vegetable oils and may cause problems in cold weather. 

When selecting a restaurant, find one that changes its oil frequently — every week or so. Using the same oil for longer periods changes the chemical composition, making it much less combustible. What you are looking for is oil that is amber in color. 

Vegetable oil is delivered to restaurants in five-gallon plastic jugs that are perfect for transporting it to your home. Restaurants may be more than willing to give you some of their used containers. If not, you’ll need to find a few containers to transfer oil from the restaurant. 

When talking with restaurant owners or managers, be sure to ask about their cleaning operations. Some restaurants clean their fryers with soapy water that is discarded with their waste oil. If their oil is contaminated with soap, you’re in for a heck of a time. Kindly request that they place oil and soapy water in separate containers. Take only the oil. Many restaurants dump their waste vegetable oil in large dumpsters out back. The oils are picked up by rendering companies. They process the waste oil into yellow grease, which they sell. Remember, rendering companies own the bins and the oil in them and have entered into contracts with the restaurants to secure their oil. So don’t help yourself — even if the restaurant owner says it’s okay. You could be arrested for theft. Instead, talk to the owner or manager to see if they will terminate the contract and give the oil to you instead. (But then you’d better be prepared to take all they produce.) 

Once you’ve taken the oil home, let it sit for a week or two undisturbed to allow particles to settle out. You can let your oil settle in 55-gallon steel drums fitted with a standpipe located six inches from the bottom; you’ll use the standpipe to drain off the clean oil. Sediment remains on the bottom of the drum. After you drain the clean oil, the bottom sludge can be combined and resettled in another drum. If you obtain high-quality waste oil, it is often not necessary to filter it. Settling works just fine. Whatever you do, do not underestimate the importance of clean veggie oil. The more energy and effort you put into cleaning your oil, the happier your car will be. Newer vehicles require higher-quality (cleaner) fuel than most older vehicles. When storing veggie oil, keep it in a cool place, out of the sun in metal or opaque plastic containers that won’t allow light in. After a couple of weeks, carefully decant the top 80 percent. Don’t pour it out. Pump it out or drain it using a standpipe. If the oil still contains particles, filter it through cloth bags rated at five microns. The bottom oil from several containers can be combined and resettled. Decant the clean oil and dump what’s left in a compost pile where it will decompose naturally. This may attract neighbors’ dogs or even coyotes, so be sure to enclose your compost pile. If you’re driving across the country and must stop for veggie oil to fill up your tank, find clean sources and/or clean it as best you can. You may want to keep a spare veggie oil tank on board for settling. (Let it settle overnight while the vehicle is stopped.) Filter the oil, then pour it in your veggie oil tank. 

For best results, be sure to check the water and fatty acid content of the oil. If water content is too high, it can seriously damage the engine. Fatty acids can also damage metals in an engine, for example copper and its alloys, such as brass. To learn more about how to measure water and fatty acids, check out Forest Gregg’s book, SVO: Powering Your Vehicle with Straight Vegetable Oil. 

The Pros and Cons of Using Straight Vegetable Oil 

Vegetable oil is a homegrown renewable fuel that offers many advantages over conventional petroleum-derived diesel and other biofuels as well. It is non-toxic, non-hazardous, and biodegradable. A spill can be sopped up with kitty litter or sawdust and safely deposited in a compost pile. 

Vegetable oil contains more energy per gallon than diesel — about 19 percent more — and much more than ethanol, natural gas, or propane. Veggie oil also has a respectable net energy yield. Net energy yield is the amount of energy released when a fuel is burned minus the amount it takes to create the fuel (i.e., grow crops, extract and process the oil, deliver it to market, etc.). The net energy efficiency of vegetable oil is twice that of biodiesel and much higher than that of gasoline and diesel. The energetics are even better for waste vegetable oil because you’re using a waste product. 

SVO burns cleaner than petro-diesel, although there hasn’t been much testing on emissions from vehicles using 100 percent vegetable oil. Emissions are also less damaging to the environment than those released from petro-diesel-powered vehicles. Because SVO contains no sulfur, you won’t be spewing sulfur dioxide into the atmosphere as you would with a conventional diesel engine. (Sulfur dioxide reacts with water vapor suspended in the atmosphere to form sulfuric acid that turns into acid rain and snow.) Soot emissions (particulates) are reportedly reduced by 40 to 60 percent compared to petro-diesel. Carbon monoxide and hydrocarbons emissions are reduced between 40 to 60 percent as well. Carbon dioxide emissions are comparable to other fuels, but are offset by new plant growth. (Plants absorb the carbon dioxide to make new plant material, including oil.) All in all, it’s estimated that veggie oil reduces carbon dioxide emissions by over 80 percent, compared to conventional diesel. 

Nitrogen oxide emissions, on the other hand, may be increased in vehicles burning straight vegetable oil. (Nitrogen oxides react with water in the atmosphere to produce nitric acid in acid rain and snow.) Fortunately, adjustments to the injection timing and engine operating temperature can reduce emissions significantly — so much so that they can be lower than those from vehicles burning petro-diesel. On the downside, running a vehicle on SVO today requires one to buy vegetable oil in bulk or, more commonly, to gather fuel from local restaurants. Although the fuel is free, it takes time to collect and clean up the fuel, both of which can be messy. 

Although there may be an ample supply of local SVO, supplies from restaurants are necessarily limited — dimming prospects of this fuel as a replacement for gasoline. In 2000, for instance, the US produced more than 2.9 billion gallons of waste vegetable oil, primarily from industrial deep fryers, such as potato processing plants, snack food factories, and fast food restaurants. Even if the entire 2.9 billion gallons were collected and used as fuel, it would replace less than one percent of US oil consumption. That said, refined vegetable oil could also be extracted from crops grown specifically to produce SVO, though that would bring with it some of the same problems presented by ethanol and production of other fuel crops. Another downside of SVO is that there is no infrastructure for it — as there is for ethanol and, to a lesser extent, biodiesel. 

SVO is currently a do-it-yourself venture or, at best, a small-group cooperative endeavor. Because the amount of used waste vegetable oil is limited, it seems unlikely that infrastructure will be created to provide this fuel commercially. Another downside emerges on long-distance trips. If you’re traveling across the country, you won’t find gas stations offering SVO. Stopping to gather vegetable oil can be very time consuming. If you can’t find a supply, you have to switch to petro-diesel or biodiesel. 

There are also some legal issues to consider. In the US, for instance, it is illegal to convert a car to run on straight vegetable oil under US EPA guidelines. Doing so could affect the emissions of a vehicle and is considered illegal tampering. Although the EPA has not fined anyone for converting a vehicle to SVO, it is still illegal. It’s also illegal to sell kits unless they’ve been certified by the EPA. So far, there are only two companies seeking certification, which is an extremely time-consuming and expensive process. 

It is also illegal in the US to sell straight vegetable oil as a fuel. Those making their own vegetable oil are required to pay federal and state highway taxes on the fuel they produce and consume. (Although it is illegal to convert a car, they’ll gladly accept your tax money.)  

Taxes on SVO vehicle fuel vary from one country to the next. Some revenue departments may not even be aware of its use or may believe that it is not significant enough to collect taxes on. In Australia, it is illegal to produce any fuel for sale unless a license is granted by the federal government. Failing to do so can result in a fine of up to $15,000 to $20,000 — and can also involve jail time! As a final note, converting your car to run on vegetable oil may void manufacturer warranties. Contact your dealer or the auto manufacturer to determine if this is the case. 

Conclusion 

News stories about people traveling across the country on veggie oil are alluring to those of us who are interested in sustainable transportation. It should be clear by now, however, that it is not quite as simple as it looks. You need to look into your options very carefully to make the right choice. I strongly recommend that you read more, especially Forest Gregg’s book. 

When purchasing a kit, bear in mind that climate plays a big role in the success of an SVO vehicle. Warmer climates are better than colder climates. In fact, in warm climates, or during warm weather in colder climates, cars can be started and run completely on vegetable oil. Purging the fuel line of SVO may not even be necessary in such instances. If you convert your vehicle to SVO, you may want to consider using a fuel injector/piston cleaner to remove carbon deposits. Pour one 12-ounce bottle into the fuel tank every six months. 

Finally, when shopping, avoid SVO systems containing copper parts, for example copper tank heat exchangers. (That’s not because the oil will damage the copper, but rather the copper will catalyze chemical reactions in the oil that result in byproducts you don’t want in your tank and engine.) When shopping, choose wisely. Buy the best kit you can afford. If you’re in the market for a diesel car, be sure it’s in good operating condition. If you buy a lemon, it will still be a lemon after you convert it to veggie oil, note the folks at Greasecar. For guidelines, see their 23-point inspection checklist posted on their website: It will help you make the proper selection of a diesel vehicle for conversion.

Reprinted with permission from Green Transportation Basics, published by New Society Publishers, 2010.