How can a Diesel Engine be Converted to Biodiesel?

Michael Pollick
Michael Pollick

The good news is that a diesel engine is already designed to accept biodiesel fuels, so it does not have to be completely overhauled to become "green." The inventor of the diesel engine, Rudolf Diesel, originally envisioned peanut oil as the engine's fuel source, but a usable petroleum-based waste oil became more commercially available. Modern diesel engines still continue to run primarily on petroleum diesel, but a number of owners are now converting to alternative fuels such as used vegetable oils collected from restaurants and food processing plants. Biodiesel conversion kits are available for diesel car owners, although they can be somewhat expensive.

Vehicles that run on diesel fuel can also use biodiesel.
Vehicles that run on diesel fuel can also use biodiesel.

When most people think of converting their car to biodiesel, what they are really considering is how to utilize used vegetables oils as a fuel. Straight vegetable oil (SVO) itself is not biodiesel. Modifications to the engine must be made before a car can accept SVO. True biodiesel is processed before it goes into the car, and is added to the gas tank like regular fuel.

The first diesel engines used peanut oil as a fuel source.
The first diesel engines used peanut oil as a fuel source.

One of the main challenges with converting a diesel engine to accept SVO fuel is the nature of the fuel itself. Food-grade vegetable oils have a tendency to thicken or solidify as the air temperature drops. To be useful as a fuel, the vegetable oil must be heated. This heating is accomplished by installing a second fuel tank in the car's trunk and running lines from the radiator to provide radiant heat. Petroleum or mixed petroleum/biodiesel fuel is stored in another tank, since it does not need to be heated.

The SVO conversion kit also includes a thermostat and fuel tank switch placed near the driver's seat. When the vegetable oil has reached an acceptable temperature, the switch is activated and the heated oil is drawn through a second fuel line into the engine block. At this point the car is being completely operated on organic fuel. The standard petroleum fuel line is shut off until the switch is reversed.

Used vegetable oil may contain a number of food particles and other contaminants, so a SVO conversion kit also contains a special filter mounted near the engine block. This filtering process ensures that only heated vegetable oil reaches the engine, which reduces the risk of clogged fuel lines and contamination of the engine block. Biodiesel fuel blends containing both petroleum and organic materials have already been filtered, so that fuel is not sent through the filter. Biodiesel blends also use oils which have been processed to remain liquefied regardless of air temperature.

There are also kits available that will convert used vegetable oil to biodiesel fuel. These are usually free-standing systems that can be housed in a garage or other outbuilding. The process of converting vegetable oils to biodiesel takes a number of steps, and can be dangerous if the proper safety precautions are not followed. Fuel created using such kits can be used by a diesel car just like regular diesel fuel.

Converting a standard diesel engine to SVO is mostly a question of providing a second fuel tank and fuel line to deliver the organic fuel to the engine. If a stable form of vegetable oil with a lower point of solidification can be developed, the need to heat the tank may be eliminated in the future. It is important to understand that SVO and biodiesel work in diesel engines, not the gas-powered internal combustion engines found in many cars.

Michael Pollick
Michael Pollick

A regular wiseGEEK contributor, Michael enjoys doing research in order to satisfy his wide-ranging curiosity about a variety of arcane topics. Before becoming a professional writer, Michael worked as an English tutor, poet, voice-over artist, and DJ.

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Discussion Comments


Short answer? Do not use bio diesel! Old or new, the bio diesel blend composition is too unstable (yes even with the official standard). Also bio diesel exhaust burns hotter and bio diesel will end up in your truck oil! Whiter than white applies here. Yes it cleans, but it cleans too well. This is why in the very fine print, truck manufacturers suggest 5 percent max biodiesel, but the truck maker’s recommendation? Don’t use bio diesel at all. The first thing that will likely cause issue with bio diesel is those relatively new exhaust burners. Yes, plain diesel has its drawbacks also: its lack of lubrication.

Given that most warranties require you to have a 45 diesel and most diesels are at 40, you would still need to get something anyhow if you plan on having a warranty. The main problem with bio diesel is its cleaning capability. It is too good at cleaning!

Check its properties versus other materials. It pretty much chews through anything but stainless and aluminum. Cast iron? Yep, it chews it too! I don't know if it is as bad as the old days cooling liquid, but I know it is very effective at cleaning!


A diesel engine does not need any modifications to run biodiesel up to about 20 percent fuel-mix (i.e. B20). Even 100 percent biodiesel (B100) can be used straight away in a diesel engine but there might be a need for some tuning in cold temperature and changing filters more often.

Using biodiesel in an engine is mostly a warranty issue and not a mechanical constraint.


All diesel engines can run on biodiesel. It's actually better for the engine than petroleum based diesel because it lubricates more. Your mileage will decrease slightly and you will also produce more NOx. Your sulfur emissions will drop to 0, and carbon dioxide emissions as well as hydrocarbons will decrease.


Vegetable oil is not biodiesel. Vegetable oil is vegetable oil, or if used (restaurant fryers) it is most commonly referred to as WVO (waste vegetable oil). Biodiesel consists of methyl esters (from the methanol) catalyzed from vegetable oil using potassium, or sodium hydroxide.

When properly produced and filtered it can run straight into a diesel without modification.


can we use airjet pipes in our cars to increase their efficiency?


Yes, there are now new "clean diesel" vehicles made by VW. I don't know if they were made before 2009. They can accept diesel or biodiesel.


can a car run on water by using a turbine?


Biodiesel is a single specific fuel created from a transesterification process involving methanol and a catalyst such as potassium hydroxide or sodium hydroxide. Vegetable oil is not biodiesel.

Most diesel engines can run on 100 percent biodiesel if the temps are over 40F biodiesel only needs to be heated if the temps are lower than the gel point of the fuel.


Nothing was said about cost. I wonder what the average cost for converting a 3/4 truck is.


you can't run it solely on biodiesel. You have to start the car on diesel and then divert the fuel to the veggie tank. if you don't the veggie oil will begin to get too thick to run through the lines. and would you believe that i'm only 18 and i drive a biodiesel i built myself?


can we make a 4 cylinder engine by using biodiesel


using biodiesel engine won't start when engine is hot?


which is the safer way to use bio diesel in diesel engine? Could we use bio diesel in the new built diesel engine?


Is there an engine specially designed for biodiesel fuels? If there is What is it and how does it work?


can a semi truck be converted to biodiesel? thank you.

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