Changed from 5W-20 to 0W-20...
 

2010 Civic sedan M/T. Have been using dealer fill 5W-20 (Quaker State) for a while now. Several days ago however, I got my hands on some Honda Genuine 0W-20 Synthetic blend oil in SN/GF-5 flavor (Conoco/Phillips blend). Ever since changing, the engine struggles less at low rpms, allowing me to short shift even more. Where as normally anything under 1700-1800rpms ended up bogging & lugging, I can now shift even lower and land in the 1500rpm range and still accelerate smoothly in that gear. Wasn't expecting to notice a difference at all. Just starting learning basic hypermile techniques so I'm interested to see how much better I can do.

It is good they are shifting to semi synthetic blends on the 2011 but I have hard time believing you would feel any difference between them, especially at eco speeds/rpm (low rpm) .There both 20w , at cold temps I can see engine running with less drag at bit but once warmed up I would think it be like the 5w20 .
When you see dyno graphs comparing synthetic to normal grades of same weight its only few hp and needs high rpm to show that .

Anyway glad its working I was thinking of trying it as temps by me are pretty cold now .

I agree Ed, might be a placebo effect...unless gaKC let his oil run way too long and it has broken down to sludge before you got it changed :-p But since he's going to a dealer and its a 2010 I kinda doubt that he has! (kudos to gaKC for starting the engine's life off with regular maintenance!)

Kansas might be cold right now, but its not THAT cold that you would have a considerable difference in feel from change the oil weight.

The only other idea that came to mind was that previous oil fill has overfilled. Or on your regular one year maintenance gaKC got a new air filter! :-p

Remember the 5W to 0W switch has its best gains at start up as the oil is "less thick" (hold that term loosely). Once the 5W-20 and the 0W-20 get to temp there should be no difference with viscosity. Do you go alot of short trips? Maybe your car never gets to full temp? My Subaru takes a solid 20 minutes of driving in winter to get everything warmed up to the point where the intake holds a stable temp and I can a best out of my eco-miles.

Edit: What is your mileage? New engines have a wear in period. And if you ever read driver logs most cars deliver better performance than when they drove off the lot (check out Car and Driver's long term tests). It is possible that your Civic's engine and trans have reached through this transition as well.

It has been super cold here for the last 2 weeks. Rarely above 20, most nights into the single digits, sometimes negatives. I only drive 15-18 minutes to work (about 60% interstate). Mileage just clicked 10K, the old oil was at 15 % life left (just under 6K). Who knows. It's supposed to be up into the 60s for the next week so I'm looking forward to better mileage. It is miserable when it is cold.

I think what is making the difference is that synthetic blended oil is more slippery than regular oil. I'm assuming the quaker state is regular oil? My train of thought is, less friction = less load on engine = less lugging at low speed