I seeking some factual info - good and bad - on the current trend thats sweeping across all the car user forums on the web - adding 2 stroke oil to diesel.  I thought this Forum could add some reality to all the "its works for me" type of posts you read elsewhere (Google it, they are endless !).  

Its the new snake oil - or is it ?  I've actually tried it in my Nissan TD42 and it does seem to have an effect.  The engine is quieter and pulls better.  Although I've not proved the lower fuel consumption bit yet, its looking good, certainly not worse.

So whats going on ?  Why does adding 2T oil to ULSD suddenly make the engine seem a different beast ?  Why does no manufacturer recommend this ?  Why does the current ULSD respond to this treatment when the fuel suppliers say the fuel already has lubricity alternatives to the sulphur thats been removed ?  Surely if a simple mix of 2T solves problems we need some facts from the fuel makers as to whats wrong with the current ULSD blend ?

Answers guys, and sorry if its already been covered, post me the link, I searched but didn't find anything.

The only thing that I do with my '91 Cummins is to use a "diesel additive" with each fill up to add a bit more lubrication to the pump since we are now using a very low sulfur content fuel. I have a bunch of 2 cycle oil...guess I could try that.  It's oil and not much different than the commercial additive...cheaper?

Don't know the exact mileage on my Dodge...Bought it new Feb. 1991 and the odometer "died" about ten years ago at 186,000...I checked the valve lash at 110,000 and change oil and fuel filters regularly. Runs just fine. Certainly has paid for itself!

You should absolutely never do this in an engine designed for ULSD. At the 200:1 ratio, your catalyst could be seeing 2.5 units of sulfur for every designed 1 unit of sulfur, turning your 250,000 mile catalyst into a 100,000 mile catalyst, voiding warranties, and opening yourself up to other trouble. At a more realistic 50:1 (or other similar 2-stroke type ratio) your catalyst could now be seeing 7 units of sulfur for every designed 1 unit of sulfur, turning your 250,000 mile catalyst into a 36,000 mile catalyst. With one good high-sulfur slug (say you add too much with a low fuel tank) and you can actually brick your catalyst within a few hundred miles (it's at least partially recoverable but the controls won't recover it because they won't know what happened).

Ultra Low Sulfer Diesel in most western countries is supposed to meet a specification for lubricity, measured by an apparatus called a High Frequency Reciporicating Rig. So prolly the best way to put your mind at ease is to get your diesel from a reputable supplier.  I have some familiarity with the test method (from a project looking at gasoline instead of diesel), and my experience is almost any lubricity improver will move it at very low levels.  0.2-0.3% of vegetable oil will boost lubricity significantly.  Although that is a pretty low level, I don't know it wouldn't affect low temperature properties or long-term injector fouling.  The commercial additives used at fuel terminals to adjust ULSD lubricity have had extensive no harm testing.  It's not hard to improve the lubricity of ULSD with additives, just expensive from a terminal point-of-view.

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