Straight Vegetable Oil (SVO) Concept Page

The following is a little bit of information on running diesel engines on straight vegetable oil (SVO) and my approach for converting in for the Pacific Northwest climate.

Any diesel engine can run on 100% straight vegetable oil, the main obstacle to doing this is that vegetable oil is much thicker than diesel at ambient temperatures. Therefore, a conversion typically refers to the installation of a secondary fuel tank for the vegetable oil (often referred to as waste vegetable oil or WVO) and a means of heating this wvo above 160 F, the temperature at which the viscosity is lowered to be comparable to regular, #2 diesel fuel. Most conversions use engine coolant as the sole heating medium to heat up the oil. Others use a combination of electric heating and coolant heating. WVO will typically solidify approx. 30 F (higher or lower depending on the percentage of saturated and hydrogenated fats), therefore in climates that encounter ambient temperature lower than 30 F (i.e. the PNW) you need to provide some means of heating everywhere the oil goes if you want to run 100% oil 100% of the time. If not, it may solidify and shut you down. It is also important to heat the oil prior to passing through the fuel filter, since cold, thick oil will quickly plug the filter and also shut you down. You can get away without providing 100% heat tracing if you run a mixture of WVO and diesel in the winter or simply plan on running on your diesel tank when it is cold enough to solidify you WVO.


1) Two tanks in better than one. It is possible to convert a vehicle to SVO using the single, originally provided fuel tank. Whereas I think this is fine in warmer climates, in the PNW I do not recommend unless you plan to only run a waste vegetable oil (wvo) mix with diesel in this single tank. If you truly want to go SVO dual tanks are the only way to go in the PNW.

2) Most convention conversions require you to start and stop your vehicle on diesel, and then switch to SVO once the engine is up to temperature. Whereas there is nothing wrong with this approach if you always use your vehicles for long distances, it is not practical for short driving distances. Therefore, I recommend using electric heaters (both 120 V and 12 v) which allow you to switch to SVO much sooner, or allow you to start and stop on SVO as long as you can plug your vehicle into 120 V for several hours prior to starting. This includes the use of a 12 volt inline fuel heater (which I manufacture and sell), a conventional 120 V block heater, a 120 V WVO tank heater and inline heat tracing for the wvo fuel lines. The following video shows how my 100 watt vegimatic 12 v inline heater can raise you fuel temperature by 35 F after a test drive.

3) My conversions typically use copper in some locations in direct contact with the WVO. There is a potential for problems with WVO in contact with copper, although I have never experienced any issues myself. It appears, under certain condition the WVO will polymerize (i.e. turn into a sticky gel) when in contact with copper. I suspect this is only a problem with poor quality wvo, likely in combination with wet oil and oil with excessive salt (i.e. a restaurant that salts the oil rather than the food after deep-frying). As I said, I have been running copper for over 1 year and have not seen any sign of polymerization, but I still recommend using aluminum  or stainless steel when possible to prevent any possibility of polymerization.

4) My conversions "loop" the fuel return line back into the fuel supply line. This eliminates the need for a separate wvo fuel return line (and required heat tracing), however, this loop does increase the time necessary to purge the WVO out of the fuel system for conventional purging with diesel prior to shutting off your engine. However, if you install the secondary electric heaters and plan on starting and stopping on SVO then this is a non issue.

5) Starting your vehicle on SVO even when pre-heated using electric heaters will be more difficult than on regular diesel. For example, it always takes me 2 attempts to start on SVO. I have a manual glow plug system, I heat the glow plugs for 5 seconds, turn over the engine while depressing for another 2 seconds, stop, depress the glow plug button for another 5 seconds, turn over again and it should start. If not, repeat. This may require replacement of your glow plugs. Some can handle this fine, others burn out. You can buy special glow plugs designed for SVO ( Otherwise, if you buy or have high quality glow plugs, you should be fine.

6) Good filtration of your wvo is important. If you process the oil yourself and/or you know that the oil you are getting is filtered and dewatered to 5 microns or less, you can get by with the factory installed filter. However, it is critical that the filter be heated. I accomplish this by running copper coils of engine coolant around my filter. You can also purchase units the route the engine coolant internally for more money. However, I recommend installing a separate, 2nd fuel filter for your WVO. Therefore, if your oil is not as clean as it should be, you will not plug up your factory filter and potentially shut you down. If you WVO filter plugs, you can switch back to diesel and keep on motoring.

Please e-mail me if you have any questions for comments: