Is Adding a 2T Oil to Diesel Fuel to Protect the Fuel Injectors a Good or a Bad Idea?

Sometimes car owners are confident that there are “secret practices” to significantly extend vehicle life. These advices are often backed by friends, neighbors, in some cases even mechanics, who are confident that car manufacturers keep these tips a secret because they want you to buy a new car and not try to preserve the state of your old one. Let’s look at a myth of this kind: the one that says that diesel fuel does not have enough lubricity to lubricate the diesel fuel injectors and adding a 2T oil to the diesel fuel extends their life.

Ideally the diesel fuel already has the necessary properties by default to protect the fuel injectors from damage. The lubricity of the diesel fuel is measured by its viscosity and wear characteristics. These properties are easily measurable in a lab and their measurement is part of the fuel quality control process. In many countries, the sulfur content of the diesel fuel had to be decreased due to environmental regulations, and this indeed decreased the fuel’s lubricity. However, in order to counterbalance this effect, lubricity increasing additives were added. In most modern countries, no diesel fuel can be marketed without such additive. So, adding a 2T oil to increase the fuel’s lubricity is first of all, not necessary.

Now that we know that adding a 2T oil to diesel fuel is unnecessary, let’s take a look at why is it harmful. The problem with 2T oils is that they have been developed with a lossy lubrication system in mind. It doesn’t matter how well the oil burns, it will eventually leave the system together with the exhaust gas. An automobile’s 4-stroke engine operates quite differently. Since the 2T oil does not burn perfectly in the engine, an excessive amount of soot is formed. The motor oil can clean this off for a while, but eventually it will become overloaded with soot as well and the soot deposits will cause engine wear. The wear particles generate more wear and the process soon becomes self-generating until the engine completely wears out.

Do yourself a favor: if you were considering adding a 2T oil to the diesel fuel of your vehicle, don’t do it! The problem that it causes is not immediately noticeable, but it will ruin the engine in the long run, none the less.

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