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  Mechanical Feature

Hot and Ready: Vegetable Oil used to Fuel Cars

Posted 1/17/2006
By Rod Collard

With gas prices projected to increase in 2006, alternative fuels are gaining popularity. Here, a researcher experiments with vegetable oil in fueling diesel-powered vehicles.

Vegetable oil is being used to fuel diesel-powered vehicles. But considering the high cost of fuel these days, maybe vegetable oil is hot enough now that it's ready to be used in other vehicles.

The Need

To reduce dependence on petroleum products, harmful exhaust emissions and - of course - save lots of money at the pump, a variety of alternative fuels and power sources are on the horizon. Most automotive manufacturers have a hybrid available and a few have electric vehicles. There is continued talk of hydrogen power, solar power and a number of fuel blends.

This article deals with an alternative fuel that will probably not be the fuel of choice by the general public. It involves running diesel engines on straight vegetable oil (SVO). We will take it one step further by burning used vegetable oil.

The idea of using cooking oil to run a diesel engine is not a new idea. In fact, Rudolph Diesel never ran diesel fuel in his diesel engine. He used various types of cooking oil such as peanut oil for fuel. This type of fuel needed to be clean and hot before it would actually run the diesel engine. This was an obstacle that made the diesel engine hard to start. It was not until after Diesel's death that a petroleum product was widely produced that made the diesel engine start much easier. It was named, appropriately enough, "diesel fuel." One hundred years ago, the petroleum product was cheaper than the vegetable oil. Consequently, the use of diesel fuel grew and the use of cooking oil in engines became almost extinct.

This article deals with running used cooking oil in diesel engines, with better quality emissions and virtually no performance differences. Exhaust emissions will, however, smell different than the common diesel smell. The exhaust will usually smell like something is cooking.

The Conversion

Basically, many diesel engines will run on clean and hot cooking oil. Some of the new direct injection and multi-valve diesel systems might be of concern. I used an older five-cylinder, turbocharged Mercedes, which seems to be very forgiving on what fuel is supplied to it. It is likely that this car can run on filtered straight vegetable oil without any alterations to the fuel system when operating in a warm climate. I attempted this over the summer and except for a couple of cool mornings, I ran it only on cooking oil. Even on the cool mornings, the engine started but needed a couple of minutes to warm up before I could accelerate down the road. In cooler weather, the engine can be started on diesel fuel and later switched to run on heated cooking oil.

Generally, warming the cooking oil to at least 100 degrees Fahrenheit with the waste heat of the engine will be hot enough to run the diesel. In this system, two separate fuel systems are used. One would be the diesel start/stop system, and the other would contain the straight vegetable oil. The idea is to start on diesel, warm up and switch to cooking oil. Then just before shutting down, switch back to diesel. This will purge the cooking oil from the lines so that the vehicle will have a supply of diesel to again start up. Expect to use a six-port switching valve to redirect the fuel line, the return line and the lift pump line. All of these lines and the tank must be heated by some means. Just heating the tank is not enough. If any lines clog up because of liquid that is too thick, the engine will not start and run.

The required temperature to liquefy the cooking oil is a variable depending on the quality of the used cooking oil. Collecting used cooking oil from Chinese restaurants can yield good results. This is partially due to the quality of the oil and the ease of filtering. Collecting the best possible cooking oil will save time and minimize aggravation.

It should be noted that dealing with used cooking oil can save you money at the pump, but will most likely be aggravating. It is easy to make a mess quickly. Used cooking oil attracts ants and varmints that might also want to "fill up" on the stuff. This article attempts to show a few ideas of how to collect, store and transfer the oil without too much of a mess.

The overall plan is to provide clean and hot cooking oil to the diesel engine. One way to accomplish this involves rerouting the cooling system heater hoses to circulate hot water through tubes in the "veggie tank." It is also necessary to heat the fuel lines all the way back to the auxiliary tank. We chose to actually run the cooking oil fuel line inside a tube located inside the heater hose, which extends or travels back to the extra tank located in the trunk. This method will better transfer heat to the fuel line than merely running the fuel line along the heater hose.

The Collection

A barrel funnel can be made easily. It has a large screened funnel at the top and it tilted back for sediment to collect.
You might relate the quality of used cooking oil to either Crisco or Wesson Oil at room temperature. Crisco is a white paste and will not flow until warmed up. Wesson cooking oil is liquid even at lower temperatures. Unfortunately, you are not always sure what quality of cooking oil you are getting. If the fuel ever solidifies in cooler climates, you will certainly be forced to walk.

A variety of methods are used in collecting used cooking oil, from a five-gallon bucket to a 250-gallon collection tank. Remember that I found Chinese restaurants to be the best place to collect used cooking oil. Most food vendors need to dispose of their used cooking oil. Many will have a storage tank out back. Some restaurants pay to have their oil hauled off, but others get paid for their used oil. This last example is probably rare.

One word of caution: Once the cooking oil is placed into the disposal tank, it is the property of the waste hauler. Even if the restaurant has granted you permission to remove the oil, it might be considered theft. This is important because some SVO enthusiasts who plan to travel long distances will need to collect oil along the way.

Friendly persuasion and diplomacy will be needed to talk to restaurant managers. Making the arrangements to get the cooking oil can be complicated if you encounter a language barrier. The few managers I have talked to are willing to give you cooking oil after a long explanation of what you are doing. One manager that I spoke to seemed to think I was with the FBI and was about to send him off to jail! Keep in mind that restaurant owners usually do not want to jeopardize their relationship with the company that removes their waste material.

You want the best of the oil while leaving the sludge for someone else to take. (Note: I have found that this discussion is usually made easier if you have just finished a meal at their restaurant.)

Some will allow you to place a small barrel near the back of the restaurant, and they will pour the cooking oil in when they can. It is important to make this activity as easy on them as possible. I made a few wide-mouth funnels out of new drain pans so they could dump two or three gallons of cooking oil in and not make a mess. It is important that no moisture or rain get into the barrel. Also, remember that full, 30-gallon barrels are difficult for one person to handle.

Those who choose to collect and store large amounts of used cooking oil could use large tanks on a trailer with equipment such as vacuum pumps or 12-volt pumps. Don't forget that gravity is your friend and try to rely on it when possible. When gathering cooking oil from stationary tanks, moisture and thicker cooking oil material will settle toward the bottom. It is always a good idea to skim off the top and avoid the lower gunk that will tend to clog things up quicker. Again, the better quality of cooking oil will save time and money partially by minimizing fuel filter replacement.

As a rule of thumb, try to filter the cooking oil each time it is transferred to another container. This can be done by different methods from using cloth and screen over a funnel to using a spin-on filter. Remember that one of the objectives of using used cooking oil is to save money. Try to use alternative filtering methods initially and save the expensive spin-on filters for the final trip into the veggie tank.

I have tried to avoid buying the spin-on filters and have used cheap cloth laid over a screen. I also use paint filters that I have received from the local auto parts store for free. These have worked well for me in warm conditions, but when transferring oil in colder temperatures, the cooking oil will clog up the filter much faster. I have tried to devise a large funnel with screen and a cloth cover that could contain at least five gallons. This method is not my favorite, however. It wastes a lot of paste-like material, which if heated, could burn and propel the engine. Containers can store the cooking oil and after a period of time, the thicker and heavier components will settle down toward the bottom. Taking the fuel off of the top is preferred, while leaving the sediment for the waste hauler.

My Favorite Method of Collecting

Many larger restaurants have recycling pumps on their deep fryers. Depending on what they are cooking, they can drain the fryer tanks and pump and filter the used oil back into the fryer tank for further use.

The ideal method for collecting used cooking oil is to have an agreement with the restaurant to pump their used oil through their filter system and into the original 4-gallon containers. These containers are usually marked as 30 pounds and are easy to handle. Be sure to mention that you can save them disposal cost and that they are helping the environment. This is a great situation if you can talk them into it.


Now that you have collected used cooking oil, there are a variety of ways to dispense the oil into the vehicle. Money can be spent on a variety of electric pumps. If you are trying to be efficient and save money, rely on gravity whenever possible.

The best method I have found so far is to heat the screened cooking oil and drain it through a filter into 5-gallon containers. These could be stored and are fairly easy to handle while filling the veggie tank. We built a heater out of a used hot water tank that seems to work very well. This also shows the larger storage tank in the background.

I have also added one more step that makes the filling process easier for me, and that is to use a radiator filler jug to fill the veggie tank. Whichever method is used to fill the tank, it is important to have a good, wide-mouth funnel that is secured. It is not fun to spill this cooking oil in the truck. Despite some disadvantages, running used cooking oil can save you money and give you a good feeling of accomplishment.

Additional information and conversion kits can be viewed at

Rod Collard is an associate professor in the Automotive Technology Program at Southern Illinois University at Carbondale, Ill. (SIUC). He is ASE certified in the areas of automobile repair.

The Automotive Technology program at SIUC has just been named the national winner of the Automotive Industry Planning Council (AIPC) Award of Excellence for 2005 for best postsecondary automotive program in the United States.

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