How to convert a VW TDI to Biodiesel
One of my Biodiesel Jetta TDI's
This title is a little misleading if you have read my post on “Using Biodiesel in your Vehicle.” In reality, I’m going to provide information on how you can prepare your VW TDI to run on biodiesel.
In general, there are two issues to overcome when running a vehicle on biodiesel:
- Biodiesel degrades some soft fuel lines that are not rated for alcohol-type fuels like ethanol, methanol and biodiesel. Any soft lines that are not compatible should be replaced to prevent premature degradation and fuel leaks.
- Older diesel vehicles develop sludge and residue in the fuel tank from diesel fuel. Biodiesel is a solvent and will dissolve the sludge sending it through the fuel system over a short period of time. This will clog fuel filters rapidly until all of the sludge is dissolved and passes through the fuel system.
I have two ’99 VW Jetta Mk IV TDI cars. Both of them have the VW 1.9 liter ALH A4 turbodiesel engine. This engine was delivered in the Volkswagen Jetta and Golf from the second half of 1999 to the end of 2003. It was also delivered in the New Beetle from 1998 to 2003. This article describes how to resolve the two issues above specific to the MkIV ALH A4 diesel engine.
Replacing the non-compatible fuel lines.
On the Mk IV engine, the only fuel hoses that are not compatible with biodiesel are the fuel return lines that are located between the injectors and the return line on the injection pump. They must be replaced with viton, fluoro-elastomer or fluoro-elastomer-lined hose. The easiest way to do this is to buy a viton return hose kit for the VW TDI MkIV from Grease works in Corvallis, Oregon. The full kit costs less than $20 and is easy to install. The second option is to buy bulk hose in the correct size from an industrial supply company and make the kit yourself. In addition to cutting the hose to fit, you will need to have a crimping tool and the correct size hose plug for the terminator on the last injector. The correct hose size is 3mm ID in “soft” consistency. The firm or hard consistency doesn’t allow for easy bending between injectors.
Cleaning out the fuel tank
Years of diesel fuel in a tank will cause sludge to form on the inside of the tank. Biodiesel is alcohol-based and serves as a solvent when introduced into the fuel tank. The sludge is dissolved into the fuel and enters the fuel lines and fuel filter. For an older vehicle, this may clog the fuel filter very quickly. Here are my recommendations on slowly cleaning the fuel tank.
- Do not use 100% biodiesel until your tank is clean. (B100) By using B20, you will slowly dissolve the diesel sludge without quickly clogging the filter.
- Use B20 for the first five tanks of fuel and then change your fuel filter. After this, you should be able to run B100 but keep a spare fuel filter with you.
- When your car starts to lack power, it’s time to change the fuel filter again. After this second change, you should be able to go back to regular fuel filter changes.
Biodiesel in blends greater than 50% work very well in the summer in Georgia. Once the temperatures drop below 40 degrees, I recommend switching to B30 or less. Biodiesel will begin to gel at temperatures under 40 degrees. Gelled biodiesel will quickly clog your fuel filter and cause a very large mess. By following the recommendations above, you should find running biodiesel a pleasant experience. It sure smells a lot better than diesel and will make you feel better about your carbon footprint.
