Join Date: Dec 2008
Location: Tyler, TX
Thanked 407 Times in 347 Posts
Diesel vs LSD vs ULSD
After Duke posted about his fuel leak on the 7.3L I decided to perform some snooping, and see what I could dig up on fuels.
As I have posted in the past, the fuels we have available in the USA are mostly crappy in terms of quality. At this time there are NO regulations for cetane, moisture content, lubricity, specific gravity etc., only on sulpher content.
Years ago the sulpher content of diesel was unregulated, and generally it was much higher than 500 ppm (parts per million). When it became evident that diesel engines would need catalyst mufflers in the early '90s, the Feds mandated that sulpher in diesel be reduced to 500ppm or less. Diesel that is 500 ppm sulpher or less is called Low Sulpher Diesel (LSD). This was to pretect the cats from damage, and to reduce the formation of sulpherdioxide, a form of acid rain.
It was believed by most that this would cause lubricity problems in the injection pumps, because sulpher was thought to add lubrication to these components. I was always skeptical of this because the exact same fuel systems are used in other parts of the world and they did not have any troubles with lower sulpher contents - but I had no test data to prove it.
Question: Did you notice that the fuel filters on older equipment, pre LSD, were often stained the color of the fuel (reddish, greenish), but would be considered "clean"?
When the LSD came into the market, it was felt that there needed to be some addatives in the fuel to 'make up for" the (presumed) reduction in lubricity due to the loss of sulpher. So how was this achieved? The refiners (not all, but it is very common) began mixing small quantities of used engine oil into the diesel. We all know engine oil is an excellant lubricant, and in very small quantities will not create any detectable exhaust smoke when mixed into fuel.
Question: Have you noticed that "black ring" on your fuel filters beginning in the mid '90s? Guess what, that is evidence of the used oil that was mixed into the fuels.
Many people are worried, or have experienced fuel leaks after switching to the new 15ppm sulpher content diesel fuel; Ultra Low Sulpher Diesel (ULSD). So far, the content of the sulpher, or the refining methods were blamed for these leaks. While it is true that ULSD is "dry" fuel, because of how the sulpher is removed with a process called Hydro-cracking, that is NOT the cause of the leaks.
The used oil mixed into the LSD fuel supplies caused the fuel seals and o-rings to SWELL because they were not designed to be in contact with OIL, but only with fuel. When ULSD is then used, the "dryness" of the fuel leaches the oil out of the seals and o-rings causing them to contact (shrink) and leak. This is also why most engine manufacturers are stating the if the egnine was run on LSD for only a "short time" there is substantially less risk of seal and o-ring leaks. Makes perfect sense to me.
Bottom line: Don't balme the ULSD, or the Feds, blame the refiners for adding things that should never have been un LSD to begin with.
Legal Disclaimer: This post in no way implicates any one refinery or retailer of fuels, it is only ment to outline the practices of some in the industry, and to make the consumer aware of this problem.
'93 F-250 HD, 7.3L IDI, 5spd - FARM TRUCK
I Support: Trailer brakes an every axle over the towing vehicle's GVW; CDLs for RVers; Safety inspections for ALL vehicles and 6 axle trucks (97K GVW proposal).
Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote - Benjamin Franklin
I vote for LIBERTY!