crazymagman

My wife watches her gas mileage religiously in her '07 TSX, and when I change the oil the mileage always seems to drop off a couple mpg's. I thought she went to a different gas station or something the first time, but after the dealer changed it and her mileage jumped from 31mpg to 33mpg consistently, then I knew something was up. I changed the oil myself here recently, and it has dropped back to 31mpg. I called the dealer and asked what oil weight they are using, and they said 5W20 on all vehicles except the turbo RDX, and it uses 5W20 synthetic.
The '07 TSX calls for 5W30, so I wonder why in the world they use 5W20?

curls

Because they can't read the oil cap, nor their own engineers' recommendations to use 5w30 in the TSX K24 engine.

Stick with 5w30 to give a slight edge towards protection of your engine, over fuel economy. But personally I don't see a huge problem if you continued to run a good quality 5w20 (synthetic preferred).

nj2pa2nc

The dealer near me in NC uses 5W20 oil on my tsx-did not change the MPG. When I have the oil changed in Pa (I try to have it done there as much as possible they use 5W30. They also told me there is nothing wrong with using the 5W20. My gas mileage went down when I put on new tires. (Yokohama Avids 4vs) My car has 90,000+ miles.

Itchytoe

Brand of oil also makes a difference. They all have very different addatives in them which change the physical properties of the oil. For example, oil that is harder to shear will result in lower fuel economy, while oil that shears easily will result in higher economy. Bear in mind that oil that shears easily isn't providing nearly the same protection to your engine as a good oil.