Easy Intro to Homemade Bio-fuels – Part Two: Straight Vegetable Oil


A plain language explanation of Biodiesel and Straight Vegetable Oil technology. No auto repair experience required.

This is part two in a series. You can find part one: Making Biodiesel, here

If you’ve already read part one, you’ll want to Click here or scroll down to Part B, or start here to refresh your knowledge of veggie oil fuel.

Part A

This intro is going to focus on diesel engines, and oil based fuels. Ethanol and other homemade fuels can be used in gasoline engines, but I have less experience/knowledge of that, and will save it for another essay.

This is not meant to be a step-by-step tutorial, but more of an introduction to and explanation of the process.

So the first thing to know then is that there are two different kinds of automobile engines, diesel and gasoline. Biodiesel and straight vegetable oil can only be used in diesel engines.

Note: In case you weren’t quite sure, Straight Vegetable Oil is just that. Pure vegetable oil. In all but a few cases, homebrew biofuel is made using waste vegetable oil. When filtered of particles and water, WVO is still quite usuable as a fuel. (Except when of lower quality from overuse and contamination.)


When Rudolph Diesel first introduced his new engine at the 1900 World Fair in Paris, it ran on peanut oil. It wasn’t until Diesel’s mysterious death 13 years later that a method was discovered to make diesel fuel from petroluem by-product (the left-overs from the gasoline production process.)

Difference between Diesel and Gasoline engines

Both kinds of engines are similiar in that they use small explosions to move pistons up and down in a cylinder. In a gasoline engine, fuel is mixed with air, compressed by pistons and ignited by sparks from spark plugs. In a diesel engine, the air is compressed first, and then the fuel is injected. The air heats up when it’s compressed, thus igniting the fuel.

This difference allows for the use of oils in a diesel engine which are much less flamable than petroleum.

Diesel engines today

Diesel engines still operate on the same basic principle as they did a hundred years ago, the main difference being that they have been engineered to handle a less thicker oil than peanut or veggie oil. (When speaking of oils, the word viscousity is used to describe the thickness of oil. Petroluem diesel is less viscous than vegetable oil, and vegetable oil has a higher viscousity than petro-diesel.)

Therefore, the process of using vegetable oil in diesel engine involves reducing the viscousity of the oil. Once this has happened, the resulting fluid is for all purposes diesel fuel.

Two processes for reducing oil viscousity

The two basic processes that you would use at home to reduce the viscousity of vegetable oil are mechanical and chemical.

The mechanical process involves heating the oil to approx. 80 degrees celsius. Straight vegetable oil conversions involve installing components into the fuel-delivery system of a diesel vehicle to heat the oil, so that it is injected into the engine at the right viscousity.

The chemical process involves using chemicals (lye and methanol) to reduce the viscousity of the oil. This process is called transesterification, and is basically the process of stripping the oil of glycerine. Once this glycerine has been removed from the oil, it is the proper viscousity for modern diesel engines, and becomes bio-diesel (see part one).

Part B: The basics of Straight Vegetable Oil conversions

Electric valves to switch from veggie oil to diesel

As I said above, converting a diesel vehicle to run on straight vegetable oil in a diesel vehicle basically requires installing components that will heat the veggie oil to 80 degrees C. The only case I’ve ever heard about of people running SVO without any conversion are in old Mercedes vehicles on hot summer days in Florida. I used to have a couple of these vehicles, and I know from experience that they can tolerate a much thicker fuel. Generally though, I would never try to run SVO without adding these additional heat sources.

There are two main ways that this heat is generated. The first is via the heat within the engine coolant. This coolant flows, via the water pump, through the engine and into the radiator. Before it hits the radiator it is approximately 80 degrees celsius. The second source of heat comes from electrical components that you install.

A fuel filter (used for veggie oil) wrapped in copper pipe.

In addition to heating the oil, components are installed to create a second tank for the veggie oil. This is because you need to start the vehicle on diesel or biodiesel and let it run for five minutes until the collant fluid is up to temperature. So the components involved here are a second tank, and valves to switch between diesel and veggie oil.

A flat plate heat exchanger (FPHE)

Heat is drawn for the coolant fluid in a few ways. The first is by tapping into the existing coolant hose and running new hose back along the veggie oil hose to the veggie oil tank (usually in the truck) and then back to the radiator. So what you end up with is three hoses bundled together, the coolant out and back and the veggie oil hose. A portion of the heat will transfer through the hoses from the coolant fluid to the oil. A lot of heat is lost in this process, thus requiring the use of the electrical components. But before I get to that, I’ll also mention that the coolant line is also wrapped around the veggie oil filter. Another component that uses coolant heat is a heat exchanger. Veggie oil flows back and forth through it in one direction, and coolant back and forth in the other direction, bringing them in contact (with metal plates between the two fluids of course) and allowing for the oil to absord even more of the heat. Another way that the coolant heat is sometimes utilized is by having the coolant line loop inside the tank. This acts generally to reduce viscousity of the oil in the tank if it is cold and too thick to pump.

The Vegtherm, an inline 12v fuel heater.

The electrical component sits close to the fuel injectors, and provides that last boost of heat to bring the oil to the right consistancy. A temp. guage is generally installed between this component to guage the heat of the oil just before it is injected into the engine.

So essentially, you are cutting and splicing hoses and wiring in a few electrical components. The conversion happens to the fuel delivery system and not to the actual engine.

An ingenious installation of the second (veggie oil) tank, utilizing the space tire storage compartment in the trunk.

His a breakdown of the components I talked about.

-A second tank for the veggie oil.
-Electric three-way valves (sometimes manual valves) to switch the fuel flow from diesel to veggie. Diesel engines also have a return line (fuel is used to cool the injectors, then is returned to the tank). So there is also a valve to switch from diesel to veggie on the return line.
-A second fuel filter just for the vegetable oil. Sometimes these are specifically designed to be coolant or electric heated, but often people will wrap them with copper piping to run the coolant fluid through.
-An electric fuel heater. This element wires straight to the battery, with a switch wired into the dashboard of the vehicle. They are generally a six inch piece of pipe with an heating strip across the top. They are sometimes homemade using the element from a stove, or the glowplug from a diesel engine.
-Fuel hose
-various brass fittings and hose clamps.
-a temperature probe/gauge

How these components fit together is the real challenge. There are dozens of configuations. Your configuration will be specific to your vehicle, but there will still be various ways the system can be configured.

Here are some examples:

Newer vehicles with onboard computers are more difficult to convert, as the computers will often throw codes (tell you something is wrong) thinking that the fuel is overheating. Not all diesels can be converted. There are Direct Injection diesels and Indirect Injection. Direct Injection diesels are problematic, as they skip a step that would otherwise heat the fuel. It’s best before considering a conversion to do research specific to your vehicle. These forums are a great resource.

For each of the components mentioned there is often a variety of choices. You can use electric valves or manual valves (which may involve stopping and lifting the hood to access the valves, or running a cable, similar to a bicycle brake line, into the cockpit). You can buy inline heaters pre-fabricated just for this purpose, or fabricate your own. You can but heated fuel filters, or make your own copper pipe wrap. You can bundle your coolant and veggie oil hoses in what is called hose-on-hose, or run a fuel hose inside a larger coolant hose (called hose-in-hose). You can choose whether to have a heated fuel pick-up or not. You can buy a kit or compile the components yourself. Like I said, do lots of research, or hire someone (like myself) who knows what they are doing. If you hire someone, be prepared to learn how the system works, or work alongside them installing it. You’ll need to know this in case you need to repair it. Your mechanic might not know how it works.

A Davco heated veggie oil filter, made specially for this purpose

Hose in Hose (HIH). Copper coolant line in rubber fuel line.

A homemade inline fuel heater using a glowplug

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