Converting a Ford Power Stroke 7.3L Diesel Engine to Vegetable Oil

Most diesel engines are capable of running on a wide variety of fuels. Several years ago I converted my 2002 Ford F250 with a 7.3L Powerstroke diesel to run on waste vegetable oil. The design was a collaboration of my own ideas combined with those of Jason Crawford’s. Since that time, Jason Crawford has continued to innovate his design, which was later to become the Vegistroke™ available from Biofuel Technologies.  This is an overview of my original conversion for those that are considering building their own conversion, or just curious how they work.

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Not all engines convert to alternative fuels exactly the same, but there often many similarities. The most two important factors for vegetable oil is that the fuel NEEDS to be clean and water free.

While it is not difficult to filter the oil, removing any miniscule / trace amounts of water can sometimes prove tricky. If the water is not fully removed it will cause cavitation in the injection pump or injectors, a form of erosion which will significantly reduce the life of those parts.

The second most important part is that you want the vegetable oil to be hot when it is injected. Heating the oil reduces the viscosity, bringing its physical properties closer to diesel and also helps to ensure complete combustion. How hot it needs to be is debated, but 160F is a typical goal.

Another important aspect of reliably using vegetable oil as a fuel is to startup and run the engine on standard diesel or biodiesel until the engine is warm and the vegetable oil is hot enough for injection. It is also important to purge all vegetable oil back out of the engine before shutdown so that the next startup can be on diesel again.

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The Ford PowerStroke Super Duty 7.3L (built by International / Navistar) has some unique advantages that set it apart for alternative fuel usage. First is the fuel injection system. These engines do not contain an injection pump. Instead they have an injector at each cylinder that uses high pressure engine oil to pressurize the fuel for injection. The injectors are fed by a fuel rail that is cast directly into the head of the engine. This is an advantage because this fuel rail acts as an extremely good final heat exchanger. This design also allows a configuration of check-valve’s to control which fuel you are using. It also enables the use of an extra valve to purge the vegetable oil from the head at shutdown, reducing the purge process to only a few seconds instead of the 10-15 minutes or more required by some engines. The major components of my original conversion are:

  • 50 Gallon marine poly tank
  • Hotstick aluminum tank heat-exchanger
  • Aeromotive A1000 Fuel Pump (I now recommend a different pump, the SVO Fuel Pump from Dinofuels Alternatives)
  • Mallory 4305M bypass Fuel Pressure Regulator
  • Davco 234+ Fuel Filter
  • Check-valved switch over per Jason’s design
  • Flat plate brick style final heat exchanger – (later removed)

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The system’s switch over is based off of Jason’s idea to use check valves and differential pressures to control switch-over and to have added reliability to the fuel system. This method keeps two independent fuel systems right up to the motor, so that in a failure with a pump or plugged filter, you can still drive on diesel. In fact, the switch over back to diesel is so smooth, you wouldn’t even know if you didn’t see it on the pressure gauge. I believe Jason has a patent on the check valve switch over method. Above is a diagram that shows the basic layout of my conversion. I simplified the diagram by leaving off the coolant hoses to the various parts. The coolant is sourced and returned via the cabin heater hoses. The final heater exchanger, aluminum fuel lines (Hose on Hose), Davco filter, and Hotstick tank heater are all heated by the coolant, in that order.  I colored the components based on which fuel is flowing through them. As you can see the stock fuel system is mostly unaltered. The only change is that instead of being routed straight from the stock filter to the heads, it goes through a check valve and into the check valve manifold instead. The stock design is to have the heads dead-headed, meaning that fuel goes into the heads at the same rate it is consumed, and the stock fuel return is from the integrated FPR (Fuel Pressure Regulator) in the stock filter housing. This is a nice plus, because it keeps oil very hot. The other side of each fuel rail in the head has a port that is plugged in the stock configuration. The WVO (Waste Vegetable Oil) FPR output is attached to these ports, and then set to a pressure high enough that it will not bypass any fuel at the stock pressure. The veggie FPR and purge valve actually have just WVO in them most of the time, but I colored them as both fuels because a small amount of diesel will pass through them during the fast purge cycle.

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I currently have a 50 gallon Moeller crossed-poly marine fuel tank for my veggie use. I welded together a frame made of 1″ square tube to mount the tank within. It is surrounded by 1″ rigid Styrofoam insulation on all 4 sides and the bottom. Also, my tank frame has a 2.5″ tall, 8′ wide opening across the bottom to allow me to still haul a few sheets of plywood, or one layer of 2″ thick lumber and use the full length of my bed. The tank frame is mounted down to the bed on each side with Grade 8 5/8″ bolts. I am using the stock tank sending unit that came with the tank I also have a hotstick tank heater connected to a 1/2″ push-lock hose to the veggie filter.

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The veggie filter is a Davco 234+. I ordered it from www.davcotec.com, and it includes the 12V heat option, though I am not sure it really adds much more heat then what the coolant heat already provides. It is installed on the vacuum side of the pump. I had read many concerns about mounting the pump this way, so I did some flow testing with the Aeromotive A1000 pump before I installed them. I ran a 3/4″ hose from a bucket of room temp WVO, to a 1/2″ alum. tube to the A1000, and then a 3/4″ hose back to the bucket. There was no regulator in this test setup, so that the pump should flow as much as it possible could. The filter seemed to flow fine, and the pump ran well without any sign of cavitating. This filter needs to be installed vertically. As this filter is quite large, I was unable to find any place to mount the filter underneath that I was happy with, so I decided to mount it along with the pump in a crossover toolbox. I mounted the relays and fuses for the pump and Davco 12V heat at the same location. I purchased the fuel pump, an Aeromotive A1000, at a local Jegs.

The fuel supply and return are both soft 1/2″ aluminum that I purchased Jegs as well. It is coolant heated in a Hose On Hose (HOH) configuration with a rubber coolant line, all ziptied into a bundle, and then wrapped in foam pipe insulation. The returning coolant line (5/8″ heater hose) is not run in the HOH bundle, because I believe the coolant returning after running through all the stuff may be colder then the oil in the lines and could actually reduce the efficiency if it was included in the bundle.

The truck runs in stock form until the coolant reaches a certain temp (I have been using appprox 160 F). Then it is safe to turn on the Aeromotive pump. The A1000 is a high pressure, high flow pump and easily pushes the hot WVO with enough pressure to close the diesel checkvalve, forcing it to just continually return through the stock FPR. The A1000 pressurizes the fuel system up to whatever pressure the WVO FPR is set to and then operates the heads in a looped return configuration. My setup is running the pressure at 70 psi at the FPR at rear of the heads; this causes a pressure of about 100 psi in front of the heads due to the high flow of the A1000. When I am ready to shut the truck off, I shut off the A1000 pump, and then open the fast purge valve for about 10-15 seconds. This causes the stock fuel pump to push all of the veg.oil out of the fuel rails, and into the veg. return line. Then I close the purge valve and the truck is again running in stock form. The only thing left to purge would be a very small amount of WVO in the injectors themselves, and should only take a few more seconds. That’s it. The truck is purged and ready to shut down in less than 30 seconds.

Below is a picture of where I tapped into the cabin heater supply hose. I just put a tee on the hose and ran the WVO circuit in parallel with the heater core. I did this so that I could attach a ball valve to each leg of the circuit. This is so that I can close the heater core off in the summer, allowing a faster WVO switchover, and so that I can close the WVO circuit off in the event that I ever develop a coolant leak.

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I mounted all the gauges and switches into a box I purchased from radio shack. I have an Autometer economy coolant temp gauge (sending unit mounted on coolant output of final H.E.), an Autometer economy Oil temp gauge (sending unit mounted in aluminum junction manifold just before heads), an Autometer digital fuel pressure gauge (sending unit mounted in same aluminum. manifold), and digital fuel tank gauge, using the marine sending unit that came with the tank.

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Here are the gauges and control switches. The first one is shortly after start up (engine was still warm), still running on diesel. Notice the fuel pressure. The second is while running on WVO. Notice the higher fuel pressure, and much higher WVO output temp of 190 F. It does not take more then a few miles to reach this temp, and stays pretty constant. The third is during a quick purge. Notice the extremely low fuel pressure. This is due to the purge valve being open, allowing the diesel to force the WVO out of the heads.

I knew virtually nothing about WVO conversions before this project, and learned most of what I needed to design and build this conversion from www.thedieselstop.com and http://biodiesel.infopop.cc. If you found this project interesting, you may also like my instructions for building a large solar generator.

I used the following vendors to purchase pretty much all of the parts:

  • Aeromotive pump, Mallory FPR, Aluminum line, Autometer gauges, many of the AN fittings: Jegs
  • Davco 234 Plus: www.davcotec.com
  • Final Heat Exchanger, checkvalves, 12V purge valve, AN fittings, other misc. www.mcmastercarr.com
  • Hotstick, Digital fuel gauge, and replacement fleetguard filters for the Davco: www.vegpower.com
  • Other fittings and miscellaneous supplies came from the local Lowes.

7 thoughts on “Converting a Ford Power Stroke 7.3L Diesel Engine to Vegetable Oil”

  1. Hi ! MARK I really like your information on your conversion, would you change anything else I have been running veggie oil mixed with diesel for sometime now but not in the winter for I live in northeast Iowa and farm so I have used it in my tractors,I would also like to get those converted , and Thank You , Kurt

  2. I’m curios as to what kind of mileage difference you are seeing (+/-) on WVO or SVO compared to straight diesel.

  3. Do you know of any place in Missouri that has knowledge of converting over a truck or 2? I have 2 7.3’s that I would like to get done with the stuff I have already purchased just can’t find a knowledgable person.

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