Question about GC vs Mobil 1 15w50

[glxpassat]

One of the specs that I look for in an oil is that it meets not only the A3/B3, but also the B4 which is a tougher diesel spec than B3. While looking at a bottle of Mobil 1 15w-50 I noticed it meets the A3/B3 spec but did not list the B4. How can a thick oil like this not hold up to the B4 spec when a thin oil like GC 0w30 can? Even if the Mobil 1 has alot of polymer VI's, would it shear to a weight less than GC? I wouldn't think so, but I guess it would. So what am I missing here?

 

[SSDude]

GC is not thin. It is almost a 40wt and sometimes oxidizes into a 40wt.

 

[yannis]

B4 refers to a better cleaning ability-more detergents.

 

[JohnBrowning]

Could also be that M1 did not test it for cert. for this rateing? You have to figure that they already have Delvac 1330,1300 and Delvac-1 wich are all diesel oils! THey may not want to compete with them selfs in the diesel market.