I noticed my mileage has dropped a bit since getting some maintenance done about a month ago: oil and drain/fill ATF at the dealer and cabin and air filters (K&N drop-in). The car is a 2011 Sport model that I bought used 3 months ago. Before the maintenance work, I was getting 30mpg mixed (mostly city), but I am getting about 25-26mpg recently on my last two fillips. Note that I'm getting all these estimates from the dash. I don't drive the car really hard, but I do use the paddles once in while and drive it bit harder when I do. I did get about 38mpg on a long trip doing about 70mph on the freeway. Should I not be concerned?

 

Maybe remove the K&N, and put the OEM filter back in and see if the Mpg goes back up.

 

I'm right there with you purist. I had Toyota flush out my Vibe and fill the tranny with the proper World Standard fluid. I was consistently getting 33 mpg around town for years. Once the procedure was done, I struggle to get 31. I was even getting 29-30 with winter gas. While 30 mpg is just fine in a Corolla engine, there is no disputing that I have knocked off close to 3 mpgs as a result of removing the NUMMI OEM World Standard fluid and putting in fresh fluid. I can't explain it, but there is is. So I propose that your issue likely has something to do with the ATF fluid transfusion you did. I recently did the same thing (drain not flush) on my 2007 Fit. I have no way of knowing what the mileage was before that because I had to get the fluid out immediately; the previous owner left the OEM fluid in for 94,000 miles. Bottom line: I think you will be just fine. There seems to be no substitute for the original fluid put in at the assembly line.

 

@YouKantPimpInaKIA: I actually found a deal on a cheap OEM air filter so I'm going to at least try to eliminate that as a possibility.

@Burntz: You're probably right that I'll be OK. It's just annoying as you probably felt with your Vibe.

Let me see how the new air filter goes in addition to doing a few more fill-ups to see if the drop is consistent.

 

Probably used a higher weight oil than you had before causing more drag inside the engine.

 

Last week upon checking the oil level, the dipstick was one quart low. After adding a quart, I immediately went from 36 mpg to 34 mpg. This was not a surprise, as I am reminded by this every time I replenish the oil. The extra quart of oil also causes extra drag as Loudbang mentions.
FYI, the ecomoders purposely run a quart low to boost their mileage numbers. I read about this, and tried it for a while when I first got my Fit, and yes my mpg did go up. However, I don't like having to check the oil all the time. Also, I got paranoid about running too low on oil.
On my 1986 Accord, I used to add oil whenever the "oil" light went on. This practice worked great, as I got 317,000+ miles on that car (BTW, it was still running strong all the way up to the time I replaced that car with the Fit). However, I discovered that the "oil pressure" warning light on my GD3 does not glow until the oil level is already below a quart low!

 

That was the other thing I was thinking. If I still can't figure it out, I will change out the oil also.

Do most owners here use the suggested 0w20? I'm considering synthetic, but I'm worried it might be overkill.

 

I don't know about "most." Synthetic is better oil and not much more, especially if you're following the MM and getting a lot of miles between changes.

0W20 makes sense too.

I switched from using conventional 5W20 (came with this new in 09) to 0W20 and noticed an improvement in MPG at the time. But it was accompanied by a change to better tires so I'm not sure what helped, but the better oil didn't hurt...

 

I haven't been able to find conventional 0W-20 oil in may area, synthetic only. Honda claims to have conventional 0W-20 but it's bulk oil, they told me they would sell me some if I bring a container. I'm not sure of what I would actually get. I went with Mobil 1 synthetic as that's all I could find at my last change

Clifton

 

Interesting that these came with 5W20 back then, but now they recommend 0W20. There seems like a possibility the dealer put in 5W20. I'll give them a call to see what they typically use.

As for synthetic, I'll probably give this a try at the next change. I've been very happy with Amsoil in my old Galant VR4 and in my S2000 currently, but I'm sure Mobil 1 would do well in the Fit also.

 

0w-20 only comes in synthetic or synthetic blend....just run synthetic most Fits only need an oil change once every 8.5K or so.

 

I usually notice the same thing too.... a little drop in MPG right after a service.... THen it will even it self out after about a month.

 

If you reset the trip odometer on the way in, that makes sense- they probably do a lot of starting and stopping and driving short distances and leaving the car running...