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 known as alternate fuels.  The pictures contained herein are products we sell. 

Our products work well with biodiesel, which will jell in cold temperatures and absorb water.  This guide will not include any information regarding the chemical process to convert veg into biodiesel.  The term veg oil or alternate fuel represents WVO, SVO, or biodiesel because the conversion components are essentially the same or very similar.

Starting with back to basics - choose a vehicle. What engine? There are lots of diesels on the used car market that run well on alternate fuel. In many cases both naturally aspirated diesel engines and turbo charged diesels work incredibly well. The indirect injection engine available in Mercedes diesel sedans and station wagons manufactured through the 1980s and imported into the US market run very well on most alternate fuels. Isuzu, Nissan, VW, and a whole range of US domestic diesel cars and trucks also are excellent. Please do not ask about specific models and years, as we are not experts in this area only to say that you can experiment with making a small investment for a heated filter.

Decide what sort of conversion to undertake. Veg is sticky.  A good flushing with diesel will clear out sticky residue to keep the fuel pump, injection pump, and injectors clean.  This is a positive, but often overlooked advantage of a 2 tank system. 

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

To be reliable, the engine needs coolant to operate, so don’t directly plumb it underneath the vehicle to a rear tank heater. 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. Safe fuel tank heating is explained later in this guide.

Veg oil will jell in cold temperatures. Jelled veg is thick enough to ruin an injection pump. If your engine’s injection system is full of jelled fuel, don’t start it. Move it to a heated environment like your garage, or wait for warmer temperatures. This happens when owners of 2 tank systems forget to purge back to diesel and park outside in freezing temperatures.

It is necessity to keep extra fuel filters in your vehicle at all times. 

When shopping for an alternate fuel filter, price the filter element before making a purchase.  It has been our experience that using a sedimentator extends filter life because a sedimentator traps water and particulate that will clog a fuel filter.  Systems without a sedimentator require more frequent filter changes than those with a sedimentator.  Many of the filters we sell take the most common element used worldwide for industrial and automotive diesel engines priced between $2 and $6 each rated at 8 - 10 micron.  If you know you will burn veg long term, look into buying filters in bulk.

If you have a BIG truck and think you need a BIG filter remember that XXL size is not a positive attribute regarding alternate fuel filters.  BIG filters cost BIG money.  Fuel filters are rated by flow and by the size of particles trapped, not by physical size.  Our filters have a flow rate of 8 -10 gallons per minute.  That's 480 to 600 gallons per hour!!!  If you are the skipper of an ocean going vessel burning veg with fuel consumption that exceeds 600 gallons per hour, don't buy any of our filters... otherwise your BIG pickup truck, bus, mobile home, semi, SUV, sedan, or small car will do just fine with our "right sized" filters.  Big filters  work against your veg conversion because the greater the distance from the hot filter head the colder the fuel inside the filter element.  Big filters facilitate cold weather jelling, fat coagulation, and premature clogging because the fuel remains unheated in the lower half of the element.  Keep your BIG wheels, but don't use a BIG fuel filter.    

Always use a sedimentator for diesel and a heated sedimentator for alternate fuel. Mount them before your fuel filters. Sediment and water do horrible things to injection systems.  It has been our experience that a sedimentator will help trap water, particulate, and animal fat. 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.  Fuel enters the cone's center and is forced down into the bottom where water, and particulate are trapped.  The fuel then moves upward and travels around the cone's edge and exits.  This "fuel current" will trap water, dangerous particles, and some animal fat that can be purged via the bottom drain.  Without a sedimentator, a higher percentage of  fat molecules, water, and particulate will collect in the fuel filter requiring more frequent changes.  Trapping sediment, water, and animal fat prior to the fuel filter will extend filter life.  If you want to know more about sedimentators, contact us with your questions. 

Burn clean fuel. We do not believe in using up throw away filter media to clean fuel, washing, drying, and separating animal fat.  If your fuel source is not clean, then 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 has individual components for DIY guys who want to build their own centrifuge.  Why spend money on throw away media when you can avoid it all together by deploying a robust centrifuge. 

When used properly, a centrifuge will remove particles from WVO down to one-half micron and can also be used to convert Used Crankcase Oil (UCO) into fuel. When UCO passes through a centrifuge, the additives that would pollute the environment and harm your engine are left in the bowl. The clean UCO can be blended 70% to 30% diesel in the summer and 30% to 70% diesel in the winter. Sending this fuel mix through the centrifuge a second time will prevent the diesel and UCO from separating.  Don't store WVO and UCO together because WVO will break down UCO and convert it to sludge. 

A centrifuge will greatly benefit those using a waste oil furnace.  Waste oil purified with a centrifuge will all but eliminate the need for annual burner cleaning.

How much can you save? It is easy to multiply your weekly fuel expenditure by 52 to calculate your  annual budget. For example: If you spend $100 a week, 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 $1,500 on a good quality Simple 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 are $4,160 every year. When some international problem disrupts fossil fuel supplies, like a confrontation with Iran and the price of diesel doubles, what happens? Your potential fuel savings will also double. Keep track of your mileage, because 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 after paying road tax you will still realize significant 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, we think it best to install individual components to fine-tune your particular vehicle. The one size fits all kit is generally not the best value 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 differ from one operating in a warmer seasonal climate.  We sell conversion components and do not offer one size fits all kits.

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 must be vented to the outside atmosphere. Never vent a fuel tank into the interior or trunk space. While the fumes are not extremely volatile, they are potentially toxic and can coat the vehicle interior with oily residue.

Putting WVO, SVO, or Biodiesel into the existing fuel tank will act as a cleaning agent removing diesel sludge from the tank bottom.  Veg oil will clog the fuel pickup screen leaving the engine fuel starved and put excessive strain on the fuel pump.  Remove the fuel pickup screen leaving the fuel pipe open so the thicker veg, sludge, particulate, and animal fat won't collect in the tank.  It is important to keep the fuel tank clean and the fuel pickup open.  Mount a sedimentator before the fuel filter and have replacement fuel filter elements with the vehicle.  We once had loose sludge when we first put WVO in 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.   Don't be discouraged if this initially happens to you. 

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. Marine tanks are available in 5, 10 gallon, and sometimes larger sizes that can be strapped down temporarily while planning a more 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 for an in tank heat exchanger, aluminum is a better choice.  Copper will dissolve over time when used with alternate fuels that are somewhat 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. Solenoid valves are 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. 

WVO, SVO, and UCO have 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 180 deg F will burn even better. Be aware that alternate fuel will cool down very quickly.  Heated fuel on its way to the engine 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 step in the right direction, but is not a full winter ready conversion for cold climates. 

Avoid the big heat exchangers designed for solar and hot water furnaces that do not have the proper mounting brackets or the correct plate spacing for alternate fuels.  These big heat exchanges loose too much heat because of their mammoth size.  We tried this type of heat exchanger and had to have something better. 

We offer compact and efficient heat exchangers that have proper mounting brackets designed for automotive use with alternate fuels.  Fuel flows in one direction through a series of stacked plates while engine coolant flows in the opposite direction.  These are manufactured from high grade aluminum with a 3 hole mounting bracket and a burst pressure of 783 pounds per square inch.

We also have a slightly larger heat exchanger (picture not shown) that is used to heat alternate fuel by extracting heat from power steering fluid, automatic transmission fluid, engine oil, or engine coolant.  It has the 3 hole mounting bracket and 2 tapered pipe thread fittings for connecting the coolant, power steering, or transmission lines.  We even have one on board our Land Rover hooked up to a fresh water tank that uses engine coolant to provide hot showers during camping trips.

Occasionally we will have a plate heat exchanger integrated with the fuel filter on the same compact housing.  These work very well, but are available in limited supply.

The key to burning alternate fuel is to have it heated enough to accomplish 6 stages. Each stage is equally critical.

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

2.) Position compact heat exchangers where required.

3.) Heat it enough for the water to separate from the fuel before reaching the sedimentator.

4.) Pass it through the heated sedimentator to trap sediment, fat, and water. 

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

6.) Have the fuel between 120 deg F and 180 deg F when it is injected into the engine.

Heat the fuel in the tank. One of the most efficient ways 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  completely isolated from the engine’s cooling system. The second system is comprised of a heated plate exchanger to transfer engine coolant heat, 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 via hot coolant and pumped back to the fuel tank heat exchanger. A ruptured line from this second system will not drain the engine coolant. The driver can switch off the circulation pump and if necessary run the engine on straight diesel. Again, the key is to maintain reliability and avoid potential breakdowns.

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 help water separate from the fuel.

The fuel then passes through a heated sedimentator where particulate and water are 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 condensation on the inner tank walls.  Some claim that a heated sedimentator will trap 99% of the water that has separated from fuel.  I always mount a sedimentator before the diesel filter and have emptied 10 ounces of water at a time from the bottom drain.  Likewise, using a heated sedimentator with alternate fuel is a necessity.   

Heated fuel filters are a must for burning alternate fuel.  In cold temperatures after being parked, a vehicle's alternate fuel filter will contain jelled fuel.  In this case, an alternate fuel filter without heat is relatively useless. 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 lone heated filter will usually work fine during warmer months, it will not be sufficient during a cold winter.  One of the benefits of a heated filter is that after being parked outside in cold temperatures jelled fuel will heat and liquefy. 

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 electric heaters for those that don't want to route engine coolant.  Fuel filters with one or more electric heaters placed to heat a large quantity of fuel and sufficiently heat the filter housing work well and are easily installed. These filters are available with single or twin filter elements.  One of the twin units is available with slightly larger elements for larger engines.  One unit 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. Mixing with gasoline is not a good idea for a variety of reasons.  If you intend to mix WVO with a volatile fuel like 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. 

Fuel Filters often clog without warning.  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 changing elements.  I personally am not one to litter.  This will 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. My wife particularly likes this option because she doesn't have to deal with changing clogged filters, stopping to fill up with diesel (ouch over $2.40 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 element 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 misrepresented as alternate fuel filters. These unheated water filters can be more trouble than they are worth in colder climates. Also avoid electric heating pads that wrap around the outside of the fuel element and coolant coils that also wrap around the fuel filter element. They heat the outside atmosphere more than the fuel.  Like electric wraps, outside coolant coils have to be removed every time you change the filter element and reapplied 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. Many diesel fuel 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 on alternate fuel.  A common misconception regarding alternate fuel systems is overheating the fuel.  It is a good idea to 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 actual fuel temperature.   In more than 10 years, we have never seen a conversion that overheated fuel, but have fixed many that were injecting fuel that was not warm enough.  Again, moving fuel cools quickly loosing heat for every inch of fuel line traveled so be sure and check the fuel temperature at multiple locations.  If the fuel cools down too much en route, position a heat exchanger to solve this problem.

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.  Switching back to diesel and allowing purge time before parking will assure the engine will start again 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 answer to the same question is no... if the sedimentator has 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. 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. Always 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 install a conversion that will send hot alternate fuel all the way to the engine.

Designing a logical layout for your alternate fuel system can be challenging. Consider all the components for your system; the type of fuel you intend to burn, and how far the fuel travels before being heated.  Locate 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.