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BACKGROUND
To the best of my knowledge, the only internal change to the 9-5's engine working parts over the years was that beginning with the 2000 model year, the LPT versions no longer had even flimsier internals. Thus, any change in recommended oil viscosity or brand is a marketing or management decision, not a technical one. At the launch, 5W40 was the highest recommended viscosity and what went in at the factory.
Now there are three main organizations setting standards for motor oil: ACEA (Europe), ILSAC (the United States and Japan), and API (for all practical purposes, international.) SAE had established the framework for viscosity ratings at the dawn of time, and all the standards organizations follow the SAE conventions for viscosity.
ILSAC tends to be very sensitive to emissions and fuel economy, and generally doesn't even rate 40 weight oils. It's somewhat telling that Mobil 1 0W-40 does, I think, have an ILSAC sticker. When you dig down to the actual numbers, the Mobil 1 sits right on the line between a 30 weight and 40 weight oil. As did (and perhaps still does) Castrol 0W30, once known as "German Castrol" as the product was imported from Europe, not blended in the USA.
ACEA seems more sensitive to the performance of the lubricant, a testament to the need for engines to hold together on the autobahn and the traditional Europeans' penchant for towing big things with small cars.
API seems to try to maintain a level playing field, but tends to be more responsive to ILSAC standards. For example, when ILSAC began limiting the phosphorous percentage in motor oil, API followed suit for viscosities that were covered by ILSAC, but not for viscosities that ILSAC didn't cover. For example, 5W40 synthetic diesel oils often carried an API gasoline engine rating despite having far more phosphorous than ILSAC allowed.
PRACTICAL MATTERS
The oil needs to do a lot of things, most of which are independent of viscosity. The one thing that requires an adequate viscosity is the fluid film that prevents metal-to-metal contact in places like the bearings, the cam and cam follower interface, and the pistons and rings. Here the design of the engine affects the viscosity requirement: larger clearance requires higher viscosity. higher temperature requires higher viscosity. sliding cam followers require higher viscosity than roller followers (and good EP properties as well).
MY RECOMMENDATION
in order of importance:
Change your oil.
Change your oil often, more often than the 10,000 mile book recommendation.
Use synthetic oil.
Use a name brand synthetic oil.
Use an oil meeting ACEA A3/B3 specification.
Use an oil with HTHS values closer to 4 than 3.5. (That pushes you toward a 5W40 oil, which is not common outside heavy duty diesel formulations. The pluses and minuses of using diesel oil are beyond the scope of this thread.)
Use a synthetic fiber mat type of filter, like a Fram Ultraguard or a Purolator "Boss". This style is superior at removing very fine particles than can result in chain wear.
posted by 65.35.8...
, Tue, 20 Feb 2018 13:19:13
1, Fri, 23 Feb 2018 22:18:28
, Tue, 20 Feb 2018 07:22:24
, Sat, 17 Feb 2018 18:25:09, Fri, 16 Feb 2018 18:15:49, Fri, 16 Feb 2018 09:40:05, Fri, 16 Feb 2018 08:55:22
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