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Old 07-23-2013, 07:59 AM   #59
bluesubie
Scooby Guru
 
Member#: 767
Join Date: Jan 2000
Chapter/Region: Tri-State
Location: N.J.
Vehicle:
04 FXT

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Even if you do a used oil analysis on a WRX factory fill, it comes back as a 20 grade and I suspect they use an extremely thin 30 grade or even a 20 grade at the factory. I know in some countries, they newer n/a Foresters allow 5W-30. In many cases, a 5W-30 and 5W-20 are made from the same base stock. The 5W-30 is just loaded with more viscosity modifiers to thicken it up which is why a 5W-20 can actually be more stable than a 5W-30 and many 5W-30's will shear to a 20 anyway.

Yes, a 0W-20 is thinner in extreme cold and will give you better fuel economy before the car is fully warmed up. So you're getting something like .25% better fuel economy for the first 5 minutes of operation. The cold cranking viscosity for a 0W is tested at -35C and a 5W is tested at -30C.

http://www.pqiamerica.com/coldcrank.htm

Of course, all 0W's aren't the same viscosity in sub-freezing temps you want one that is thinner on the MRV test at -40C. Looking through product data sheets is one way to find MRV.

http://www.swri.org/4org/d08/global/...vs/default.htm

http://www.mobiloil.com/USA-English/...mpability.aspx

Of course, it can be tricky trying to compare oil specs since some companies list CCS and others list MRV.

http://www.mobil.com/USA-English/Lub...l_Economy.aspx

http://www.eneos.us/product/1

A viscosity graph can be helpful as well and you just enter the 40C and 100C Kinematic Viscosity. It's just less accurate below 0C but it gives you a good idea of actual viscosity.

http://www.widman.biz/English/Calculators/Graph.html

-Dennis
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Last edited by bluesubie; 07-23-2013 at 08:19 AM.
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