Diesels run cleaner now?

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Jan 21, 2003
Elizabeth City NC
I have owned several Mercedes diesels 1972,1977,1980 and one of the things I ran into was the recomended oil change interval. At the time I owned these cars the manual and dealers recomended 1/2 the distance for oil changes. The gas Mercedes recomended 6000 miles changes and the diesel recomended 3000 miles changes. The thinking was that diesels had more junk that would get in the oil and needed quicker changes. Is this still true today with the newer Diesels??
I don't know if the difference would be in the engines or in the lubricant itself. I would think that the newer engines would be harder on oil since they now use EGR valves to reduce emissions. This dumps even more dirt into the combustion process. The lube manufacturers have reformulated their blends to handle this increase in soot better than ever before. I own two Volkswagen diesel cars.. one is a newer Golf TDI ('99 model) and one is a old Rabbit ('82 model). My newer Golf holds 4.5 liters of oil and my old Rabbit holds only 3 liters. It is easy to see how the oil sump on the Rabbit could become contaminated quickly. With 5000 mile oil change intervals using CF rated 10W/15W-40 oil the little Rabbit has been plugging along for 21 years.
The newer diesels run much cleaner. The fuel is burnt more efficiently so less soot is produced. This equates to cleaner exhaust, cleaner oil, less wear on engine. HL
The difference is the fuel. Back in the '70s and 80's, diesel contained much more sulfur (as much as 3%). The limit in North America has been 500 ppm for the past 10 years.
So are they now less oil-abusive than gasoline engines? The reason I ask is because of the new GM-LL-A/B-025 oil specs. The gasoline spec ("A" version) is for 30k km, while the diesel spec ("B" version) is for 50k km. I'd think the shorter interval would go to whichever engine was more oil-abusive.
Diesel lube has a more robust additive package, and often diesels have a larger oil sump. Diesels are dirtier than gasoline engines, but for these reasons the oils can handle it. Anybody here worked on both engines?...it takes a lot more scrubbing to get the diesel's black stuff off your hands. Check this thread about diesel lube in a big truck for 25,000 miles and still no need to drain the oil. http://theoildrop.server101.com/ubb/ultimatebb.php?ubb=get_topic;f=26;t=000022#000000 Ken
Ken2, This difference in drain intervals is achieved using the same ACEA "A3/B4" rated passenger car oils.... I believe the primary reason for the longer drain intervals achievable with TDI diesel engines is that their average fuel efficiency is 50%-60% higher than a comparable gas engine. As a result the # of combustion by-products getting into the crankcase is much lower. This also results in less thermal and oxidative stress on the oil. For example, the VW TDI diesel gets approx 50 mpg, whereas the 2.0L VW gas engine gets about 30 mpg. Drain intervals for these two engines in Europe are 50,000km and 30,000km respectively ....Sump sizes are 4.7 qts vs 4.2 qts, so that also contributes to the longer drain interval in the passenger car diesel engines ...Finally, fuel dilution with (reformulated) gasoline tends to degrade oil more than does diesel fuel (at least for on-road low sulphur fuels) TS
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