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Converting an RV to Run on Vegetable Oil

Left tank is 140-gallon clean tank, right tank is 70-gallon dewatering tank with attached filter extended for changing. Click to enlarge.

Frybrid has converted a 40-foot Bluebird motorhome to use straight or waste vegetable oil (SVO or WVO) in its 11-liter, 450hp turbodiesel engine. This system has a 140-gallon heated clean tank and a 70-gallon dewatering and filtering tank, bag filter which extends for changing, and 50-foot hose reel and pump to suck up oil.

The system switches to VO and simultaneously activates a pump which circulates cooling diesel fuel through the fuel system electronics package which is about the size of a briefcase. It is capable of collecting, dewatering and filtering oil as the vehicle is moving and is fitted with additional electronic heaters to allow filtering when parked. It should be capable of filtering 140 gallons of waste oil a day, according to Frybrid.

Using vegetable oil as a fuel in a modern diesel engine has two challenges: the viscosity of vegetable oil is unsuitable for use in modern fuel injectors; and the polymerization of vegetable oil when it hits hot metal at below a certain temperature threshold. The oil must be heated to 160° F to reduce its viscosity to a point comparable to that of diesel, and the engine must reach 180° F before the oil is injected to avoid the polymerization problem.

Since we have an engine which is cooled with coolant (50% Distilled water, 50% Ethylene Glycol) we have an abundance of coolant which has been heated to 180° F by the time the engine is up to operating temperature, we have a ready heat source. Since the engine must be at has an operating temp of 180° F we have met the requirements set by problem #2 (engine at temp), and by using a coolant to fuel heat exchanger with the coolant being 180° F we can easily produce fuel at above 160° F meeting the requirements of problem #1.

So we will need to have a vehicle with two independent fuel systems, one for Diesel (or Biodiesel) and one for the vegetable oil. We will start the vehicle on diesel fuel and run it on that fuel until we are at operating temperature, at this point we can supply vegetable oil at better than 160F and can switch the fuel supply. Of course when we shut the vehicle down the fuel system will still be filled with vegetable oil, which will cool and become useless as a fuel prohibiting us from restarting the vehicle as the conditions to solve problems 1 & 2 are no longer being met. To solve this issue we will need to purge the vegetable oil in the fuel system with diesel before we shut the engine off.

—from the Frybrid website

The vehicle starts on diesel until the engine and coolant reach the appropriate temperatures, then switches over to VO. To avoid startup problems, the fuel system needs to be purged of VO prior to shutdown.

While some VO systems rely on only a small in-tank heat exchanger to heat all the fuel in the tank to injection temperature, the Frybrid system uses four heaters:

  • A welded high-efficiency coiled heat exchanger in the aluminum, baffled tank with the fuel pickup positioned directly in its center. This assures that all fuel being drawn from the tank is liquefied and lessens the strain on the injection pump and or fuel pump. All internal tank connections for both fuel and coolant are TIG welded to insure a leak-proof system. The integral fuel reservoir prevents fuel starvation when cornering, stopping or accelerating when low on fuel. None of the metals in contact with the fuel tank are reactive and the heat exchanger has more than 30 sq ft of surface area.

  • A heated fuel line connected directly to the top of the fuel tank.

  • A heated fuel filter, which incorporates a 14-plate flow through heat exchanger through which all fuel must flow before being filtered. This unit heats the fuel very efficiently insuring that the filter will not slow the flow of fuel even in cold climates and utilizes a readily available diesel filter element with an integral drain.

  • A final fuel heat exchanger which on its own is capable of getting all fuel used by the engine to injection temperature as soon as the engines coolant is at 180° F.

Frybrid’s solid-state vegetable oil fuel system controller monitors engine coolant temperature and seamlessly switches the engines fuel supply from diesel or biodiesel to vegetable oil only when the vegetable oil is at the proper temperature preventing the injection of cold vegetable oil which results in engine damage.

The controller also warns the operator if the vehicle is shut down on vegetable oil, provides system status indicators and automates the purge cycle allowing for faster engine shutdown.

(A hat-tip to Forest!)




I have a few of friends that run a greasecar kit. It's very similar to a frybrid kit. After many years with no problems I have to say it works.


They do not mention the ancillary benefit of in-house McNuggets, donuts or fish and chips once the SVO is at temp.


On one hand, this is a brilliant setup and a good application of the technology. RV's are driven primarily on the highway at long periods, rather than short periods where this heating of SVO would never actually occur.

But on the other hand...
MOST RV use is morally reprehensible.
They get what...2-5 miles per gallon?
For what? So the view out your kitchen window can change every minute? Take a car and stay in a hotel for christ sake! The cost of the hotel per night is about about 30 gallons or under 100 miles of driving would cost.

A savvy independant trucker though, could put the frybrid tech to good use, provided there are enough McDonald's along their route.


1. If people are going to use motor homes, at least they should fuel them in a less problematic manner.

2. Agreeing with your second comment, I think this provides a good test bed for a technology that can be deployed elsewhere.

3. Does any given McDonalds location produce 100 gallons of waste vegetable oil per day? If it is not possible to "tank up" in one stop, I don't think people will find it worthwhile to try this thing. For the dedicated "hobbyist," of course, there will always be some demand. But that's not a larger solution to the world's problems.

Roger Pham

Considering the extra cost of de-esterification of veg. oil into diesel fuel, long-haul trucks, boats, buses can run on algae oil, or rapeseed or palm oil straight as-is with duel fuel source as featured in this article. The infrequent start and stop of these HDV making this approach more economical by using straight vegetable oil (SVO).

Hal Barnes

How come everybody forgets the tax obligation fot highway use taxes (fed) and assorte astate taxes??


Tax obligations are tax obligations. In this situation, you theoretically log all the SVO or WVO you put into your tank and send a check to the taxing authority at the end of the month. If you are on a long-distance trip, perhaps you should be sending checks to different jurisdictions along the way.

In practice, of course, the tax authorities pretty much do not audit this process at all. If the use of WVO becomes mainstream, I suppose that some modifications will be made available in the tax scheme to both make it easier to use and more enforceable. That's largely a bridge to cross if and when we get to it.

A more substantial problem -- which has periodically received attention here -- is the general case: What do we do for road revenues if and when MPG goes up substantially / electric vehicles become an important part of the fleet? To a certain extent, higher MPG cars will likely be smaller and lighter, reducing wear-and-tear and maintenance needs. But beyond that point, my guess is that we will need to expand the collection of tolls, registration taxes and other user fees to pay for our road system. Such an approach, at any rate, would probably be superior to paying for roads out of general revenues.


Tax revenue? How about taking the oil subsidies we taxpayers all shell over to Shell et-al and redistribute to the road fund. That's incentive for fry-brid users to register their miles with the D.O.T.! Could use the E-Z-Pass to track miles??

Good Luck Earth!


Pretty interesting, but there are some misconceptions in this article unfortunately. Polymerization is the process of the vegetable oil turning into a rubber substance (dirty frying pan) related to the iodine content in the oil and the presence of air. In fact, heat accelerates polymerization, as does contact with metal, but you need air for it to happen. In the case of a closed fuel system, the risk of polymerization is the fuel tanks, which will have vents and access to air. The risk up front is actually coaking, not polymerization, and that would be from cold starts with cold oil in which it is forced into the injection system without being fully heated. This conversion looks great, but we need to get the facts straight.

another question: do you pay your road tax through fuel on your bicycle? how about your electric car? I just mailed my check yesterday for pushing my wheelbarrow of mulch down the street. 1.50 taxable movement.

Ed Wellington

I am new to making biodiesel and have been running it in my 2002 Ford F-350 for a few months now without problem. I was just offered 175 gallons of polymerized WVO from someone who says it won't run in their picky truck. Would this even be usable?



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