Custom Energy Solutions for the post-petroleum era Evergreen Motors, LLC
368 High Street
Greenfield, MA 01301
(413) 772-3131

Frequently Asked Questions

  1. Alternative transportation in general
  2. Modifying a diesel vehicle to run on VO
  3. Vegetable Oil as a fuel source
  4. Driving and maintenance with a VO system
  5. VO filtration
  6. Troubleshooting/Common Problems


  • Why alternative transportation?
    There are lots of good reasons… To name a few, there are environmental concerns, the desire for less expensive energy, an interest in sustainable options, and the fascination of new technologies. Many of us want to change our energy consumption and become free from the tyranny of foreign oil. Alternative transportation is a good place to start!

  • What are my options?
    Where do you want to start? You can save money and resources by walking, biking, or carpooling instead of driving alone. Live in a city? Ditch the car and use your public transportation! Rent a ZipCar for going farther afield. If you drive a gasoline car, make sure it’s a fuel-efficient model. And if you drive a diesel, consider adding biodiesel to the mix – even a small amount will lubricate the engine and do wonders for your emissions. You can even modify your diesel to run on 100 % pure vegetable oil!

  • Can you really run a diesel engine on vegetable oil?
    Yes, it’s true! Rudolf Diesel designed his engine to run on a variety of fuels, including vegetable oil (VO). When VO is heated to the proper temperature, its properties (such as viscosity) are very much like those of petro-diesel… So VO burns efficiently, just like diesel, and it smells nice, too.

  • What is the difference between biodiesel and VO?
    We think of biodiesel as a “transition” fuel. You can use it just like petro-diesel, putting it directly into your diesel fuel tank. Biodiesel is vegetable oil that has been chemically altered so that its molecular structure mimics that of diesel fuel. It can be used straight (“B100”) or mixed with diesel in various ratios (“B20”, “B40”, etc.). Vegetable Oil, on the other hand, is not chemically treated. It is just filtered vegetable oil. It requires specific conditions (namely, controlled temperature) in order to burn efficiently and not create problems with the vehicle’s fuel system. Here is where the conversion kit comes in. Most conversion kits allow you to keep your diesel and VO separate, and to switch back and forth between them.

  • Is there a diesel hybrid out there somewhere?
    Some European companies like Citroen and Mercedes are working on it. Will the technology come to North America? We hope so… Stay tuned!

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  • How does it work?
    At Evergreen Motors, we promote a 2-tank conversion system. This system has heated components to get the vegetable oil up to a proper combustion temperature (140-190 F). You start the vehicle in “diesel” mode, pulling fuel from the factory diesel tank, then switch over to the “veggie” tank when the system is heated up. At the end of your drive, you switch to a “backflush” or “purge” mode, which flushes the system with diesel again.

  • How much will it cost to modify my vehicle?
    This depends on the vehicle model and year, as well as the specific components you want installed. Installs at Evergreen Motors start at $850.

  • Will the new system affect my factory warranty?
    This depends somewhat on your dealer. Running biodiesel in excess of 20% will void many factory warranties. Running a VO fuel system does create modifications to your fuel and coolant systems, so the warranty on these components would likely be voided. But all other parts of your warranty should remain in effect.

  • Can any vehicle be modified to run on VO?
    Gasoline engines cannot be modified to run on VO. Any diesel engine is a candidate for VO modification.

  • Can’t I just put VO in my factory diesel tank?
    We don’t recommend it. Why not? For one, there’s no heat in your diesel tank. Secondly, VO and diesel do not mix well. And thirdly… ummm, there’s no heat in your diesel tank! The whole idea of the two-tank system is to get your VO up to the proper temperature for combustion.

  • What if I want to modify my factory tank instead of adding a second tank for VO?
    We’ve seen this done successfully, but the legality of modifying a stock fuel tank is questionable.

  • What kind of mileage/horsepower/torque will I get with a modified vehicle?
    It should not differ significantly from that of an unmodified vehicle.

  • Why do some VO systems have a “backflush” feature?
    This has to do with the properties of vegetable oil. When hot, it’s a great lubricant for moving engine parts, and it burns beautifully. But when cooling, VO can leave a nasty residue in fuel lines, injectors, and filters. To say nothing of what happens when it gets cold and solidifies! The backflush or “purge” setting of a VO system actually takes diesel fuel and pushes it backwards through the injectors, veggie fuel filter, and veggie fuel lines, all the way back to the veggie tank. When the engine is shut down, the fuel system is flushed with diesel and ready for the next start-up.

  • Does a VO system require added maintenance?
    You’ll need to change your VO filter from time to time, follow the manufacturer recommendations for running the system, and monitor the quality of your VO. These 3 things will go a long way towards keeping your system trouble-free.

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  • Is vegetable oil safe to use in a diesel engine?
    Yes! Rudolf Diesel tested his very efficient engine with a variety of fuels, including petroleum oils and vegetable oils. Vegetable oils burn best at temperatures between 140° and 190°F.

  • Is VO legally a fuel?
    Technically, no. Like biodiesel a few years ago, vegetable oil has yet to be tested and ASTM-standardized. Surely the promise of road-tax revenue will help to change this status in the future.

  • What emissions are produced?
    Compared with diesel, burning VO produces less carbon, no sulfur, and less carbon monoxide.

  • What type of vegetable oil is best?
    Non-hydrogenated oils with low cloud-point are the easiest to filter and handle. Canola (AKA rapeseed) is the standard-bearer in Europe.

  • Where will I find VO to use for fuel?
    Restaurants that fry with large quantities of oil are a good place to start, if you want to recycle. There is also a growing supply of ready-filtered waste VO and non-food-grade oils on the market.

  • How do I filter waste VO?
    There are loads of filtration resources online… and for every kind of budget. There are the commercially-available filtration systems with heaters, pumps, centrifuges, hoses, bells, and whistles. And then there’s the brown-paper-bag method. The main idea is this: You have a filter in your VO fuel system. You want to remove all water and large particles from your oil pre-fuel-tank, as well as smaller particles that would quickly clog up the fuel lines and filter. You want your oil to remain molecularly intact. So no excessive heating or really long-term storage. We recommend filtering to at least 5 microns. Let your oil settle after each filtration. Cold filtration advocates say it’s slower but removes waxy substances that will later find their way to your inline fuel filter. Heated-oil fans will tell you it makes the oil more pourable because it melts those same waxy substances, and helps dissipate any water that’s been mixed in. Filter as well as you can, because the future of your fuel system depends on it.

  • Can I buy WVO that has already been filtered?
    We sell beautifully filtered (~half-micron) waste oil here at our shop. It’s becoming more and more readily available nationwide. and the National VegOil Board are good resources for finding WVO.

  • Is it safe to carry containers of vegetable oil in the car?
    Absolutely. Vegetable oil is not volatile, corrosive, or noxious in any way.

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  • How often should I change my veggie fuel filter?
    Somewhere between 500 and 5,000 miles. It really is that variable! If your vehicle is getting sluggish on veggie, it could be time to change the filter.

  • Where can I get replacement fuel filters?
    Find out what kind of filter your manufacturer recommends, and your local auto parts store may be able to get it or cross-reference it.

  • How do I change my filter?
    Change your filter according to the manufacturer directions, then start the vehicle in “backflush” mode. Let it run for a minute to completely backflush the VO system (including the filter), and you’re good to go.

  • Should my mileage/horsepower/torque vary while driving on VO?
    Not noticeably. You should see roughly the same mileage per gallon as with (bio)diesel, and similar horsepower/torque.

  • When can I switch over from diesel to VO?
    Some systems now come with computers that will monitor this for you! Basically, the controllers make sure that both the engine and the VO are warmed up adequately. You can monitor this yourself by watching the engine temperature on your dash and/or the fuel temperature via an easily-installed temperature gauge.

  • Can I stop and restart the car in “veggie” mode?
    Yes, for very short periods. For longer stops (longer than 10-15 minutes), you should backflush the system and drive a mile on diesel before shutting down the engine.

  • How long should I backflush at the end of a drive?
    This may vary from 10 to 60 seconds, depending on your vehicle and the fuel routing of your system. You should follow the rcommendation of your manufacturer or installer on this one. Don’t skimp on the backflush!

  • Why the final mile on diesel?
    VO is a great fuel and engine lubricant, but only at very warm temperatures. It is imperative that you flush the veggie back to the VO tank and then “rinse” the fuel system with some diesel driving. The next time you start up your engine, it will be primed with diesel and ready to go.

  • Are there ways of heating up my car/truck faster so I can switch to veggie sooner?
    Yes and no. Insulation, in-line heaters, plug-in coolant heaters, and glow-plug heaters have all been utilized to speed up the process. But if your engine is not yet to operating temperature, bottom line is you gotta wait.

  • I’ve had my VO system for a year. What general maintenance should I be doing?
    Aside from routine vehicle care, you should have your VO system checked annually for wear and tear. Make sure the coolant system is working well, check the soundness of fittings, clamps, and valves, as well as the electrical components of the system. It’s a good idea to look inside your VO fuel tank to monitor the accumulation of greasy deposits (this is especially important if you also run biodiesel).

  • Are there any problems with running VO in colder climates?
    Vehicles can be set up with a VO system in any climate. In colder weather, we must pay closer attention to optimizing and insulating the heating system. We recommend longer backflushing in the winter. Also, collecting and filtering very cold vegetable oil can present some challenges to the winter greaser.

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  • How do I get started with filtering WVO?
    Most conversion kit manufacturers have exhaustive and informative instructions on how to approach restaurants and how to effectively filter waste veg. oil. Start with your manufacturer’s suggestions.

  • Do I need to buy an expensive filtration system to be sure I am getting clean oil?
    No. With a little research, you can put together a great filtration system that suits your needs in terms of space and capacity.

  • How small does my filter gauge need to be for good, clean oil?
    We recommend getting your oil filtered to between 1-5 microns.

  • Why do some people heat their oil to filter it?
    Heating the oil helps it to flow better, and may help to sublimate any water that’s mixed in. You will see a longer filter life (in your filtration system) with heated oil, since heating melts down any waxes in the oil.

  • Is cold filtration better?
    Cold filtration takes longer than heated filtration, but fans say it results in cleaner oil and less waxy substances building up in the vehicle’s VO filter.

  • I want the ability to filter on the road. Are the commercially-available on-board filtration systems any good?
    On-board filtration is a necessity if you’re traveling long distances and want to keep fueling along the way. We are still awaiting the perfect on-board system, because they all have their quirks. Some are made to hook permanently into your vehicle’s coolant system. Others are more portable. If you are planning to filter on the road, expect to go through a lot of filters. Even the coolant-heated filters can’t liquefy large quantities of dumpster grease efficiently.

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  • My mechanic is not familiar with the VO fuel system. Can s/he still do regular work on my car?
    Absolutely. A VO fuel system should not interfere with access to other systems in your vehicle. At Evergreen Motors, we prioritize a clean, user-friendly installation, for both the driver and his/her regular mechanic. Our install work is oriented so that important components of your vehicle are not cluttered or blocked by VO parts. Also, we are always happy to consult with technicians who have questions or concerns about the components and/or operation of the VO system.

  • My VO fuel gauge seems to be jumping all over the place. Is it broken?
    Probably not. Some fuel senders have a limited number of points that actually register on the gauge, so if fuel is sloshing between two points on the sender, it may cause your gauge to jump. There are other fuel senders that give a continuous reading, and these products are much more reliable.

  • My vehicle occasionally stalls while in VO mode. What should I do?
    It might be time to change the filter. If that doesn’t fix your problem, there may be particles clogging the fuel line… Especially if you are running biodiesel in the factory tank. You’ll need to drain the veggie tank and take a look inside. Are there chunks of dried-up vegetable oil hanging around? Crickets or leaves? We’ve seen it all! Cleaning out the veggie tank (don’t use water!) often takes care of some mysterious fuel-flow problems.

  • Even though I filter my oil well, there is be a layer of scum growing in the storage tank. What is the problem?
    This might be some microbial development, which happens all the time in diesel, biodiesel, and veggie oils. Use a biocide to prevent these organisms from colonizing your fuel supply and your car’s fuel system. There are many available on the market.

  • I backflushed for more than the recommended time, and now there is a lot of diesel fuel in my veggie tank. What should I do?
    It’s perfectly ok to have some diesel in the veggie tank. It will burn off in time. The real problem with backflushing too long is potentially overfilling your VO tank… This can be messy! If you’re having trouble keeping track of backflush time, consider getting a kitchen timer with a preset buzzer, or upgrade to a fuel system computer that monitors switchover and backflush time for you.

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© 2007 Evergreen Motors LLC