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I'm not convinvced SM is an improvement Posted by MI-Roger [Email] ![]() ![]() In Reply to: SL, jeff in MD, Wed, 13 Apr 2011 03:38:15 Members do not see ads below this line. - Help Keep This Site Online - Signup |
SM rated oils contain reduced amounts of anti-wear additives, such as ZDDP. These additives were removed from some weights of motor oils because they can foul catalytic converters if the engine is burning excessive amounts of oil.
Sort of like padlocking the barn door after the horse has been stolen. If the engine is burning oil, it is already polluting so much that it may not make any difference if the converter is operational. Any car spewing a cloud of blue smoke probably won't be long for this world anyway.
I have read that some wieghts of oil can carry the SM rating AND contain the higher previous limits of these antiwear additives. These sources identify 5W/40 as one such weight as it is primarily now specified for diesel engine use, and diesel engines are highly dependent upon these additives for long life. Internet spread urban rumor or truth? I don't know.
I haven't heard what changes were made to create the new SN grade.
posted by 198.208.15...
_______________________________________ Saabs owned: 2008 9-5 Aero Sedan, sold at 227K miles 2006 9-3SC 2.0T - Wife's daily driver 2000 Viggen Convertible - Sold May, 2022 1964 Quantum IV Formula Car - Retirement project 2000 9-5lpt Sedan, sold at 318K miles
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