Oil preferences?
 

Just purchased an 03 civic. Does everyone run Honda recommended weight? It seems really thin...

I'm going to run full synthetic regardless.

What do you run in your civic?

Honda recommended viscosity. You really can't go wrong, especially if using synthetic oil.

i use 15W-40. got 120k miles so i like the thicker oil

I spoke to a Mobil chemist a while back. He told me that the most important number is the first one. a 5W-20 oil, for example will "pump up" to pressure much faster than a 10W or 15W-XX oil, even at 70 degrees F. He went to say that most engine wear occurs during startup and yes, even at 70 degrees F.

If you have an engine with over 75,000 miles on it, high mileage-specific oil may help slow down leaks but there are many brands of high-mileage oil with 5W-30 or 10W-30 viscosity. 15W-40 is more of a racing oil.

Run the Honda recommended... I work for Acura and I've seen what happens to motors when they aren't properly maintained. Engineers don't do extensive studies on what oil viscosity works the best in engines for nothing. The recommended oil is what performs best in the engine, yes it isn't detrimental to put 5w30 instead of 5w20 once, but in the long run you will be hurting your engine. Honda doesn't just pull the numbers out of their ass, each engine has a different recommendation and I say follow it. In my Civic and CRV I run Mobil 1 full synthetic, I get it through work and Mobil 1 makes Honda's fluids. Just because it seems thin to you doesn't mean change it, the engineers are paid big bucks to know what is right, so believe them and what they say.