Written by RDAVISINVA.

How to convert your diesel to run on Waste Vegetable Oil (WVO), Straight Vegetable Oil (SVO), Used Crankcase Oil (UCO), or some mixture of these are known as alternate fuels for the purposes of this guide.  The pictures contained herein are of products we currently have for sale. 

Biodiesel will jell in cold temperatures and absorb water.  Much of the information contained in this article will also apply to biodiesel, but there will not be any information regarding the chemical processing to convert veg oil into biodiesel.  The term veg oil or alternate fuel is used herein which you can translate to WVO, SVO, or biodiesel to pertain to your conversion or potential conversion.  Please note: that some people report that when biodiesel is mixed with WVO or SVO, it causes glycerin to separate from the WVO or SVO and quickly clog the system.  To be safe, this is something to avoid.  

Starting with back to basics - is choosing a vehicle. I will make no attempt to endorse any particular engine, but at times will share my knowledge of certain vehicles and engines.

What engine should I use? There are lots of diesels available on the used car market that run very well on alternate fuel. Diesel engines that use a direct injection pump to both move and pressurize fuel based on individual injection timing settings (with or without a turbo) work incredibly well. This type of engine is available in Mercedes diesel sedans and station wagons manufactured through the 1980s and imported into the US market. Isuzu, Nissan, VW, and a whole range of US domestic diesel cars and trucks also are excellent runners on alternate fuels. Please do not ask me about specific models and years, as I am no expert in this area only to say that you can experiment with making a small investment for a heated filter to get started.

I have supplied heated filters to individuals with common rail diesel injection systems that have had success with alternate fuels. This article will not address common rail diesel injection except to mention that some people suggest that alternate fuel should be filtered down to about 2 micron for good results and longevity with common rail use only because the vehicle manufacturer required it for diesel. I neither support nor dispute this claim. My experience is that direct injection systems work fine with 6, 8, or 10 micron filters.  Common rail systems and some direct injection engines use a much higher pressure fuel pump.  Always consider that alternate fuel is thicker than diesel, so 2-micron media will clog much faster that 8 or 10 micron.  Most vehicle manufactures use 2 or 5 micron filters to prevent particles from etching (wearing down) injection components under increased diesel fuel pressure.  In this way the vehicle manufactures feel more comfortable with the long extended warranty they used as a sales pitch to lure buyers to open their wallet.  Alternate fuel cushions particle wear because it is thicker, even when heated.  Picture a room with a super ball bouncing around, the ball is a particle and the room pressurized fuel.  Now picture the same room filled with a gas that is 10 times thicker than air.  The super ball will bounce, but at less than half the speed and thus force when compared to the air filled room.  While this scenario is purely hypothetical, the concept does apply to burning alternate fuel that will lubricate injection components and diminish violent particle movement.  The most common cause of injection component wear is fuel containing water and the second most common cause is large particulate including ferrous metal particles.  Over 99% of water and particulate can be trapped and held by mounting a sedimentator before the fuel filter.  More on this later...

Once you choose a particular vehicle, then you have to decide on what sort of conversion to undertake. Because these alternate fuels are sticky, a good flushing with diesel will clear out sticky residue to help keep the fuel pump, injection pump, and injectors free of the sticky veg residue.  This is a great, but often overlooked advantage of a 2 tank system. 

I have debated conversion designs for years and always follow a few common principles as follows:

To be reliable, the engine needs coolant to operate, so don’t directly plumb it underneath the vehicle from the engine to a rear tank as a heating source for alternate fuel. A broken coolant line directly routed from the engine to the other end of the vehicle results in a breakdown. Likewise it is a bad idea to pump liquid subject to cooling system pressure into fuel tanks. Successful alternative fuel tank heating is listed later in this guide.

Veg oil will jell in cold temperatures. Jelled veg is so thick that it can ruin an injection pump. If your engine’s injection system is full of jelled fuel, don’t ever try and start it. Move it to a heated environment like your garage, or wait for warmer temperatures. This can happen when owners of 2 tank systems forget to purge back to diesel and park outside overnight with below freezing temperatures. Starting an injection system full of jelled alternative fuel can bend or break injection pump vanes and thus ruin the injection pump.

It is a good idea to keep extra fuel filters in your vehicle at all times. 

When shopping for an alternate fuel filter, it is a good idea to price the element before making a purchase.  Expect that you will be changing the element more frequently than with diesel, usually every 1,500 miles.  If you think you need a 2 - 5 micron filter, remember that all fuels swell filter media and that veg oil swells media faster than most fuels.  The smaller the micron rating, the more frequent the filter changes.  Many of the filters I sell take the most common element used worldwide for industrial and automotive diesel engines priced between $3 and $6 each rated at 8 - 10 micron.  If you know you will burn veg long term, look into buying filters in bulk. 

Always use a sedimentator for your diesel and a heated sedimentator for your alternate fuel. Mount both of them before your fuel filter. The sedimentator will not only trap sediment, but will trap water. Water does horrible things to fuel injection systems. Sedimentators are well worth the investment and will add reliability and longevity to your engine.  If you plan to burn UCO then put a strong magnet in your sedimentator to trap any ferrous metal particles.  Strong compact magnets are used in computer disc drives and are somewhat easy to remove.  They generally fit nicely in a sedimentator.  How does a sedimentator work?  A sedimentator looks like a fuel filter, but contains an open space.  At the top of the open space is an inverted funnel shaped cone.  The fuel enters in the center of the cone and is forced down to the bottom where water and particulate settle out and are left behind.  The fuel then moves upward where it travels around the edge of the cone and exits.  This "fuel current" will trap water and dangerous particles that can be purged via the bottom drain.  I always use a sedimentator for diesel and a heated sedimentator for alternate fuel.  Trapping sediment and water prior to the fuel filter will extend the filter life no matter what fuel your engine burns.  If you want to know more about sedimentators, contact me with your questions.  We have sedimentators in stock after selling out of the first 2 batches. 

Always burn clean fuel. I do not believe in using up large quantities of throw away filter media to clean fuel, washing, drying, and separating animal fat. Try and find a good clean low fat fuel source if you are burning WVO. Dirty WVO and/or UCO contain lots of grit, sediment, and fat (WVO only) that will clog an expensive fuel filter in seconds. If your fuel source is not clean, then it will be best to invest in a centrifuge that will separate the fuel from contaminate without the messy filter media to purchase and dispose of.  Simple Centrifuge sells a high quality "turn key" unit at a very reasonable price and also has individual components for those DIY guys who want to build their own centrifuge. 

How much can I potentially save? It is very easy to multiply your weekly fuel expenditure by 52 to annually calculate your potential yearly budget. For example: If you spend $100 a week in fuel, you have $5,200 a year in potential savings. If your driving habits prove that you can burn alternate fuel 80% of the time, then your savings is $4,160 annually. If you spend $2,300 on a good quality centrifuge, and $1,600 on an alternate fuel conversion, your break even point is less than a year.  After the break even point, your potential savings is $4,160 every year. When an international problem disrupts fossil fuel supplies, like a problem with Iran and the price of diesel doubles, what happens? Your potential fuel savings will also double. Keep track of your mileage, it would be a good idea to pay state and federal road tax. State and federal road tax is less than $0.50 a gallon in most states and results in more than $4 a gallon savings while making alternate fuel usage completely legal.

How should I convert? There are many ways to convert. The DIY mechanic can buy a complete conversion kit or buy various components and install them. Because most vehicles are different, I think it best to install individual components to fine-tune your particular vehicle. The one size fits all kit is generally not the best choice and usually is replaced over time as the owner becomes more knowledgeable and thus more sophisticated. Also, the conversion requirement for a vehicle in a cold climate will be different from one operating in a warmer seasonal climate.

The fuel tank. Decide if it is possible to use the stock fuel tank for alternate fuel and add a second tank for diesel. Consider that both diesel and alternate fuel have distinct smells that can be unpleasant. Tanks will need to be vented to the outside atmosphere. Never vent a fuel tank into the interior or trunk space of a vehicle. While the fumes are not extremely volatile, they are potentially toxic.

Putting WVO, SVO, or Biodiesel into the existing fuel tank will act as a cleaning agent making any diesel sludge available to be sucked into the fuel line.  This is another good reason to mount a sedimentator before the fuel filter and have replacement filter elements with the vehicle.  We once had this issue with a Mercedes 300TD Wagon and needed to empty the sedimentator a half dozen times and change the fuel filter element in just a few hundred miles before the fuel cleared up.   Remember not to be discouraged if this initially happens when you use some form of veg for the first time in an older vehicle. 

Steel, aluminum, and stainless are good choices for a fuel tank. Mounting an extra tank in the trunk is common. All tanks over 6 U.S. gallons should have an internal baffle that eliminates fuel sloshing to maintain vehicle stability. Avoid short flat tanks that allow fuel to slosh so much that air can enter the pickup pipe and stall the engine.

Decide where to mount a tank and work out the install. Don’t be afraid to experiment with a cheap temporary mounted tank in the trunk. All metal marine fuel tanks come in 5 gallon, 10 gallon, and sometimes larger sizes that you can strap down temporarily while you are planning a permanent solution. When designing the alternate fuel tank, be sure and include an in-tank heat exchanger to warm the fuel using hot antifreeze. These are usually built as coiled pipe. Do not use copper pipe for an in tank heat exchanger, aluminum is a better choice.  Copper will dissolve over time when used with alternate fuels that are acidic.

Use a fuel changeover valve to switch from diesel to alternate fuel and back again. The preferred valves are switched by a 12V solenoid. Two 12V solenoid valves are required, one for the main fuel source and one for the return line. The 12V solenoid valve for the return line is best positioned as close as possible to the engine. Proper sequencing of the 2 valves will need to be calculated, timed, and tested to minimize the quantity of alternate fuel making its way into the diesel tank and vise versa.  The multi-port valves work fine to change fuel direction, but mix a high volume of fuel.   Individual valves can be fine tuned to minimize fuel mixing on 2 tank systems.

WVO, SVO, and UCO alternate fuels need to be heated to burn efficiently without creating excess exhaust pollution, coking injectors, and so on. Alternate fuels should be at least 120 deg F at the injectors. Alternate fuel heated to 200 deg F will burn even better. Be aware that alternate fuel will cool down very quickly.  Heated fuel on its way to the injectors will loose heat for every inch of fuel line traveled. Imagine the cooling capacity of air flow at highway speeds, under cold conditions. Having a heated sedimentator and/or heated filter will keep the fuel inside the unit flowing and prevent jelling.  A sedimentator and/or heated filter is a big step in the right direction, but is not a full winter ready conversion kit for cold climates. 

There are efficient heat exchangers composed of stacked plates that are very efficient. Fuel flows in one direction while engine coolant flows in the opposite direction. The resulting converging flow heats the fuel very quickly and efficiently. Remember that bigger (large plates) and taller (more plates) are not always better. For example: 180 deg F coolant flowing through a heat exchanger will only raise the fuel temperature to 180 deg F under the best of circumstances. If the fuel reaches 180 deg F on the first plate of a large 20 plate exchanger, it will exit plate 20 at or near 180 deg F. Likewise if it reaches 180 deg F on the very last plate of a small compact exchanger, it still exits at 180 deg F.  Don't use heat exchangers designed for water or anti-freeze manufactured for solar and hot water furnaces that do not have proper plate spacing or mounting brackets and are too bulky for automotive use.  We used the big bulky exchangers and had to have something better.  We now have proven  compact efficient heat exchangers that are designed for automotive use with the correct spacing between the plates for alternate fuels that will not clog up.  If you want more information, contact us.  We occasionally list them and can set up a buy it now for you if you decide to purchase one.

Occasionally we will have a small plate heat exchanger integrated with the fuel filter on the same compact housing.  These work very well, but are available in limited supply and when they are gone, we are unlikely to obtain more.

The key to burning alternate fuel is to have it heated enough to accomplish 5 stages. Each stage is equally critical.

1.) Heat it enough to flow out of the fuel tank.

2.) Heat it enough so the water begins to separate from the fuel before reaching the sedimentator.

3.) Pass it through the heated sedimentator to trap sediment and water. 

4.) Pass the alternate fuel through a heated fuel filter.

5.) Have the fuel between 120 deg F and 200 deg F when it is injected into the engine.

Heat the fuel in the tank. The most efficient way to heat fuel is with engine coolant. It is impractical to run pressurized engine coolant from the engine back to the fuel tank, but how can the fuel tank be heated with engine coolant? The answer is to have a second system filled with antifreeze that is completely isolated from the engine’s cooling system. The second system is comprised of a heat exchanger, a circulation pump, an in tank heat exchanger (mounted inside the alternate fuel tank), and an overflow tank with filler cap. When switched on, the circulation pump will circulate antifreeze through the heat exchanger where it is heated by hot engine coolant and pumped back to heat the fuel in the fuel tank via the in tank heat exchanger. A ruptured line from this second system will not drain the engine coolant so the engine continues to run. The driver can switch off the circulation pump and if necessary run the engine on straight diesel. Again, the key here is to maintain reliability by avoiding potential breakdown risks.

Once the alternate fuel reaches the engine compartment, it should run through a heat exchanger where it is heated to at least 140 deg F to force water to participate out. Engine coolant should flow through the heat exchanger in the opposite direction as the fuel.

The fuel then passes through a heated sedimentator where particulate and water is trapped. Water will cause excessive injection pump wear and etch injector openings as well as deteriorate fuel quality causing power loss and injector tip coking. Gray or white exhaust means you are pushing water through your engine even though your fuel looks clean.  Additional water is introduced when the fuel inside the tank is heated by a tank heater or by warm fuel entering through the return line. Once the fuel in the tank is heated, it will absorb water as it cools down and mixes with the water condensing on the inner tank walls.  Some people claim that a heated sedimentator will trap al least 99% of the water that has separated from fuel.  I always mount a sedimentator before the filter when running straight diesel and have emptied 10 ounces of water at a time from the bottom drain of the sedimentator.  Likewise, I have had similar experience with using a heated sedimentator with alternate fuel.  Without a sedimentator water will go through the fuel filter swelling the filter element and choking the passages to a point where veg oil will stop flowing.  If you are burning UCO, again place some magnets in the sedimentator to trap any ferrous particles so they are not injected into the engine.  Old computer hard drives are an excellent source for incredibility strong compact magnets. 

Heated fuel filters are a must for burning alternate fuel.  An alternate fuel filter without heat is useless and should never be used. Remember that a heated fuel filter is NOT a complete alternate fuel conversion.  People contact me frequently thinking that the single fuel filter they have purchased will be enough for a complete conversion.  While using a heated filter without anything else to heat the fuel will usually work fine during warmer months, it is not sufficient during a cold winter.  The purpose of a heated filter is after being parked outside in cold temperatures jelled fuel will heat up and liquefy and when the engine is running fuel will be warm enough to move on to the next stage.  

Some heated fuel filters use engine coolant as a heat source. The coolant is routed to flow through the filter housing. Some of these filters offer a supplemental electric heater that can be used to preheat the fuel before the engine warms up and also supplement the coolant heating.

There are also fuel filter units that offer an electric heater for those that don't want to route engine coolant through a fuel filter.  Fuel filters with one or more electric heaters placed where they can heat a large quantity of fuel and sufficiently heat the filter housing work well and are easily installed. One of these units we offer manufactured by Lucas has a hand priming pump for purging air from the fuel system using elbow grease.  Do not use electric heaters with gasoline, ethanol, or any fuel mix containing similar volatile fuels.  Some people promote mixing alternate fuels with gasoline.  If you intend to mix WVO with gasoline, then use a coolant heated filter and do not connect a supplemental electric heater. 

Stay away from plastic filter units that easily break when dropped or crack over time from constantly heating up and cooling down.  Many plastic heaters manufactured by Racor and Davco contain internal copper tubing that will dissolve over time and should not be used with alternate fuels. 

Avoid remote oil filter units that have been relabeled as WVO or SVO filters. Oil filters contain a bypass valve because where engine oil is concerned, unfiltered oil is better than no oil. So when an oil filter clogs the bypass valve opens and lets unfiltered oil lubricate the critical engine components preventing engine failure. This same bypass technology is disastrous for alternate fuel systems. Never use an engine oil filter as a fuel filter because when clogged, unfiltered fuel will ruin your injectors and injection pump.  The last thing you want is unfiltered fuel damaging an expensive injection system. When an alternate fuel filter clogs, it is best for the engine to die. The driver will notice a lack of power and switch to diesel. Then the alternate filter element can be replaced when it is most convenient.

Consider mounting additional selection valves for two alternate fuel filters.  That way when the filter being used clogs, you can switch over to the second filter and change the clogged one out when it is convenient.  This avoids having to decide what to do with the old filter when you find yourself on the side of the road making a filter change.  I personally am not one to litter.  Like the conversion, this will also pay for itself by minimizing your diesel usage.  Instead of switching over to diesel you can switch to the second filter and continue to burn alternate fuel.  Be sure and wire the change over switch to route current to the second filter and not the first if you are using electricity to heat the fuel. This is a feature my wife particularly likes because she doesn't have to deal with changing a clogged filter, stopping to fill up with diesel (ouch $5 a gal), or getting stuck somewhere.  She simply flips the veg filter change over switch and continues to drive.  She asks me to do the dirty work when she gets home.  I change the filter and dispose of it properly.  With a fresh filter in place she can switch back whenever the second filter clogs.

Be aware of household well water filters being sold as alternate fuel filters. These unheated water filters are more trouble than they are worth and quickly clog when used for WVO or UCO. Also avoid electric heaters that wrap around the outside of the fuel element and coolant coils that also wrap around the outside of the fuel filter and heat the outside atmosphere more than the fuel.  Like electric wraps, outside coolant coils that wrap around the filter have to be removed with each filter element change and then reapplied to the new filter making them more trouble than they are worth.

Avoid electric heated filters with gimmick thermo switches that attach to the outside housing of the filter effected more by outside temperature, filter housing temperature, than by the actual fuel temperature. Direct injection systems and Turbo Diesel injection systems pump fuel at full capacity through the filter and return it to the fuel tank sometimes using less than 1% of the moving fuel. As long as the engine is running and thus pumping fuel, there is no risk of overheating the fuel so don't be afraid to wire a 12V heater to stay on when the engine is running.  One of the biggest misconceptions surrounding conversions is that the fuel will overheat before it reaches the engine.  For those that think the fuel is being overheated, purchase an infrared temperature gun and check the outside temperature of the fuel filter, fuel line, return line, and so on.  You may want to open a fuel fitting and check the real temperature of the fuel if you think it is too hot.  In more than 10 years, I have never seen a conversion that overheated fuel, but have fixed dozens of conversions that suffered from injecting fuel that was not warm enough.  Again, remember that fuel cools quickly and will loose heat for every inch of fuel line traveled. 

The last step in routing the alternate fuel is to make sure it enters the engine as hot as possible. The fuel change over valve should be mounted as close to the engine as possible and the alternate fuel should be heated just before entering the valve.

Cold weather preparation must be considered when designing an alternate fuel conversion. Many enthusiasts will make a small investment by installing a heated filter during the warmer months and using the fuel savings to purchase additional components to make their vehicle "winter ready". Even in northern areas, Mercedes diesel owners will purchase a dual heated fuel filter from us and use a single tank system during the summer to save money. Then use the savings to buy a sedimentator, second fuel tank, fuel changeover valves, heat exchangers, and so on.  This helps those of us on a budget. 

In winter, always remember to start the engine on diesel and switch over to alternate fuel after the engine has sufficiently warmed up.  Switch back to diesel just before shutting down and parking the vehicle.  This will assure that the engine will start in cold temperatures.

Take a few minutes to analyze all the information presented here and the purpose of each component in your conversion. Think about the order of the components and their relationship and thus interdependencies.

As an example: we often get questions from people asking if a single or dual 12V heated sedimentator will remove all the suspended emulsified water from veg oil? The answer is that it depends. What do you mean... you didn't answer my question?

If the veg is heated to 180 deg F by a heat exchanger before it passes through the sedimentator, the answer is definitely yes (provided the sedimentator is not filled to the top with water already - remember that trapped water needs to be drained).

The sedimentator heater is to prevent the warm oil from cooling down and absorbing the water that separates out starting at about 130 deg F.

The answer to the same question is no... if the sedimentator is having 45 deg F veg oil entering with lots of suspended emulsified water.

The dual heated sedimentators that use engine coolant along with an electric heater will do a much better job to settle out and trap a high percentage of the water with the 45 deg F veg oil flowing in. The same dual heated sedimentator placed just after an efficient heat exchanger will not work any more efficiently that the less expensive single or dual 12V heated sedimentator. Remember to make efficient use of your conversion components and place them in the proper order.

Don't be disappointed because you expect stellar results from components that are positioned where they cannot perform well. Likewise avoid ordering your conversion components with over kill.  Remember to use a heated sedimentator and a heated filter at a minimum and to have a setup that will send hot alternate fuel to your engine.

Designing a logical layout for the alternate fuel system conversion can be a challenge. Consider all the components for your system; the type of fuel you intend to burn, the selection valves, sedimentators, filters, heat exchangers, the circulation pump, and overflow tank. Set up your conversion to a high standard for long term reliability.

If you find this guide useful, please rate it as being helpful as it took some time to write.