1999-2009 [Subscribe to Daily Digest] |
Friction modifers do not require low viscosity oil, nor do low viscosity oils require friction modifiers. The modifiers are required by ILSAC, an industry governing body which addresses only certain viscosity range oils.
Not all lubricated parts are separated by a hydrodynamic film. Friction modifiers address those parts (like sliding cam followers, chain-and-sprocket, and roller element bearings). Friction modifiers are required by ILSAC GF "starburst" specifications, and ILSAC only covers oils ranging from 0W20 to 10W30. Friction modifiers *may* be included in heavier oils, which would earn them the "energy saving" designation on the API "donut" on the label. Friction modifiers do nothing to improve lubrication and wear - they are for fuel savings.
Main and rod bearing lubrication is controlled by the "HTHS" viscosity of the oil (high temperature, high shear), which is uncontrolled by ILSAC and API designations. SAE specifies a HTHS viscosity of 4.0 or so for SAE 40 and above single grades, and 15W40 and 20W50 grades, but for 10W40 and below it allows HTHS to be as low as 3.5. ACEA A3/B3, requires at least 3.7. There are 0W30 synthetic and 5W30 synthetic blend oils which meet ACEA A3/B3, and those could be more suitable for Saab Turbo cars than an XW-40 oil which fails to meet ACEA A3/B3 specs.
IF you want to be safe, use Amsoil 5W40, as it meets GM LL 025A, ACEA A3/B3, API SL and CI-4, and a host of other vehicle-specific specs. That covers each and every specification that Saab has ever published. Note however that to meet these specs, Amsoil has paid to have the test sequences run, and you will be compensating for that in the price of the oil. Oils such as Shell Rotella synthetic 5W40 or Mobil 1 "Truck" 5W40, which are API SL and and CI-4, might well meet the other tests if their respective refiners chose to pay for the test. API CI-4 is pretty stringent in terms of wear protection, shear stability, and engine cleanliness, and any oil which meets it has to be pretty good oil. In the end, though, it's your car and you (and successor owners, if any) who will live with the consequences of the choice.
You might look at http://www.lubrizol.com and follow the links to their "knowledge base." Note that the "knowledge base" part of site requires IE 5.X or above - it will not work with Netscape.
posted by 65.25.68...
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