The diesel injectors and pumps in your Tdi are designed to last the lifetime of the car. Just like every engine component, lubrication is an issue. At Karmakanix, we strongly recommend consistent usage of a good fuel additive. Over time, the sulfur content of diesel fuel has been cut back to lower the pollutants emitted from diesel engines, as they were a primary cause of acid rain. However, the sulfur was the major source of lubrication in the diesel fuel. The injectors and fuel pumps of diesel fuel systems are entirely lubricated and cooled by the fuel, as there is no connection to the engine oil system.
Fuel manufacturers won’t talk specifically about what they might have done to restore lubricity to their fuels. All diesel must meet minimum standards for lubricity, which is defined as a maximum size of a wear scar during a test which rubs metal together. California requirements for diesel fuel limit the content of sulfur and other lubricating aromatics beyond the requirements of other states. Many states have mandated 5% biodiesel, or BD 5, as a requirement. Most vehicle manufacturers including Volkswagen and Audi recommend using 5% biodiesel and/or additives to lubricate the diesel fuel systems. Even 2% biodiesel (BD2) yields lubricity better than early diesel fuel from last century with a high sulfur content. So far, California has not mandated any biodiesel due to liability and reliability issues.
The early VW Tdi diesel injectors up through 2003 differ greatly from the Pump Duse and Common Rail systems of this epoch, but all are prone to wear damage over time. And occasionally we see sudden and dramatic failures due to lubricity issues. Whether you drive a Jetta Tdi or a Q7, you probably want to keep your fuel system intact. Karmakanix highly recommends the consistent use of fuel additives. Even fuel manufacturers warn against some bogus additives that can do much more harm than good. We recommend Stanadyne, Redline and Amsoil as the additives you can trust to keep your Tdi alive for the long haul. Stanadyne is the preferred additive of most authorized Bosch Diesel Service Centers.