I've had my oil changed at the dealership (Bianco) since I got my WRX. Now that Bianco is shut down, I've been doing it myslef. Bianco (Marin county Ca.) has been putting 10-30 in it. I read through the owners manual and it said 5-30 prefered. I though, might as well give it a try. It made a big difference. The car is definately quicker. I'm not sure why, but it just seems like the engine revs quicker and runs smoother. I'll never go back to 10-30.

 

depending where you are located quite a few people use 10-30. kind of depends on the temperature of the area, but 5w is supposed to be smoother i believe.

 

Hmm, my manual suggested 10W30
Guess next time I'll give 5W30 a shot

BTW, does your engine sound different after changing your oil? Just curious is all...

 

my car came with 5W-30, but mine is an 04, so was there a change in the oil weights from 02 and 03 to 04? i have recently done my first oil change and put in Redline 5W-30 synth

 

5w30

 

you should run oil based on the climate and type of driving you do.

hotter climates and more aggressive driving (aka track days) should use a heavier oil and colder climates or everyday driving should use a lighter oil.

there isnt' much difference between 5w-30 and 10w-30. living in the bay area, you can use either and there isn't much of a difference. if you live in areas like phoenix or las vegas, i would not run 5w-30 during the summer time. and vice versa i would not run 10w-30 in minnesota during the winter.

lighter oil breaks down at a lower temperature than heavier ones. but the lighter oil does warm up to normal operating temp faster and is easier to start up the engine, especially during winter months.

for me personally, i usually run 5w-30 in the winter and 10w-30 in the summer. i have even run 15w-50 when i was doing a lot of hard driving in really hot summers

 

^^^
What he said