2 Stroke Oil

There are a lot of arguments, mostly on motoring forums, about whether or not to add 2 stroke oil to diesel powered vehicles. The main argument is that this will improve the lubricity of the fuel, particularly low sulphur(50ppm/10ppm) diesel.

Sulphur occurs naturally in oil. It is undesirable for various reasons. The main reason is that the sulphur from the exhaust pipe forms sulphuric acid in the atmosphere which results in acid rain. In the vehicle it pollutes the engine oil reducing its life. Using a low sulphur diesel reduces both the environmental pollution and the pollution of engine oil. In order to produce low sulphur diesel, the sulphur has to be removed and the process that removes the sulphur reduces the lubricity of the diesel. Diesel pumps and injectors rely on this to keep them lubricated.

Should I add 2 Stroke Oil to my diesel to improve its lubricity?

In short, you shouldn't. 2 Stroke Oil is designed for 2 stroke motorcycle engines, not 4 stroke vehicles. Vehicle manufacturers and fuel refining companies all agree that running 2 Stroke Oil in fuel is likely to cause complications and there have been reports of engine failures due to 2 Stroke Oil sludging up valves and fouling injectors. As fuel refineries have produced lower sulphur diesel, so too have they added lubrication substitutes to the new diesels to the point that lubrication is now even higher than that of high sulphur diesel.

The vehicle manufacturers don't recommend putting 2 Stroke Oil in your diesel...
The fuel companies don't recommend putting 2 Stroke Oil in your diesel...
The 2 Stroke Oil manufacturers don't recommend putting 2 Stroke Oil in your diesel,
   therefore it is a simple deduction that there is no reason to add 2 Stroke Oil to your diesel!

For a detailed study on adding 2-stroke oil to diesel, please see: 2-Stroke Oil In Diesel – A Technical Study. This is the most substantive, peer-reviewed study done to date that doesn't rely on anecdotal evidence.

Diesel Lubricity Lab Test

The best way to improve diesel lubricity is to use an additive specifically designed for that purpose. To demonstrate this, we decided to test one of these products to see how much of an improvement you can get. For comparison purposes we decided to also test 2 Stroke Oil.

We went to our nearest forecourt and purchased 50ppm diesel for the test. We then sourced a bottle of JASO FC 2 Stroke Oil and added it to the diesel at a ratio of 1:200 (5ml 2 Stroke Oil to 1 litre of diesel). Finally we sourced a bottle of NF Diesel Lubricity+ and mixed it according to the instructions on the bottle at a ratio of 1:2000 (1ml NF Lubricity+ to 2 litres of diesel).

The 3 samples were sent to an independent, accredited laboratory for testing on a High Frequency Reciprocating Rig (HFRR). The HFRR is used to measure diesel lubricity by rubbing a steel ball on a plate in a bath of fuel. The ball develops a flat spot over the course of the test which is called the wear scar, the diameter of which is the measure of diesel lubricity. All diesel sold in South Africa must pass this test with a maximum wear scar of 460 microns which ensures adequate lubricity for all diesel fuel systems. The 50ppm Forecourt diesel passed the test by a decent margin with a wear scar diameter of 363 microns. Surprisingly, the 50ppm diesel with 2 Stroke Oil actually decreased the lubricity by around 10% with a wear scar diameter of 396 microns. The NF Diesel Lubricity+ impressed by improving lubricity by around 33% with a wear scar diameter of 243 microns:

Diesel Lubricity Test Graph

In conclusion, we would definitely suggest using a properly developed diesel additive over 2 stroke oil as proven by this particular test.