Originally Posted By: Zako2
Originally Posted By: 90Notch
Well I went over the service history and the car has been running on Chevron 5w30 conventional for the better part of its life with no ill effects!
I think you most likely know that Saab 9-2 is using a Subaru engine (it's a Saabaru ;p), so you can find a lot of information on subaru community web sites as well as here.
"Ill effect" is hard to measure. If the engine runs its whole life on "wrong" kind of oil, the ill effect could be, for example, that it dies at 150K miles. But that's hard to observe if you don't keep the car so long. A common wisdom seems like turbocharged engines are harder on oil, so they should preferably use synthetic or at least synthetic blend oil. Some people follow "thicker is better" philosophy.
The problem with conventional oils is that they are more likely than synthetic oils to shear (lose viscosity). A lot of conventional 5W30 oils shear down and become a 5W20 after just one or two thousand miles. Some people feel uncomfortable with this. But then again, what matters more is whether the engine wear is low or high, which should be possible to find out with used oil analysis reports. Still, if you look at some UOAs for synthetic oils, such as Mobil 1 5W30 or 0W-40, they often show some shear, but the oil still stays within the designated grade (good sign).
+1. And if you go look at some of the technical forums on some of the Subaru community sites (IWSTI, nasioc, legacygt) you will find more than one recent blown turbo thread from someone running Energy/Resource Conserving 5W-30. An oil discussion can go on for weeks and then someone posts a new thread out of the blue about turbo or bearing failure.
One thing in the Aero's favor is the 2.0T isn't quite as tough on oil as the 2.5T, but Subaru of America does recommend synthetic in all turbos.
-Dennis