Below average winter mileage - 07 Civic - 107k miles

I'm worried about the transmission service that the dealer performed and that it's now hesitating to go into 5th gear, does the transmission slip at all? That would cause loss of gas mileage. Have you changed the fuel filter? Also cause a of loss of gas mileage. giving your car antibiotics doesn't really work such as fuel additives ect. The best thing to give your vehicle is the best of everything premium fuel would be a good start.

at 107,000 miles the service recommendations are as follows:

Air Cleaner Removal/Installation

Disconnect the MAF sensor/IAT sensor connector (A).
Fig 1: Disconnecting MAF Sensor/IAT Sensor Connector
Remove the air cleaner housing cover (B).
Remove the air cleaner element (C) from the air cleaner housing (D).
Loosen the bolt (E), and the pipe (F).
Remove the air cleaner housing.
Install the parts in the reverse order of removal.

Air Cleaner Element Inspection/Replacement

Open the air cleaner housing cover (A).
Fig 2: Opening Air Cleaner Housing Cover
Remove the air cleaner element (B) from the air cleaner housing (C).
Check the air cleaner element for damage or clogging. If there is damage or clogging, replace the air cleaner element.
NOTE: Do not use compressed air to clean the air cleaner element.
Install the parts in the reverse order of removal.
Install the parts in the reverse order of removal.
If you did not replace the air cleaner element, this procedure is complete.
If the maintenance minder required air cleaner element replacement, reset the maintenance minder.
If the idle speed fluctuates, do the idle speed inspection.

Dust and Pollen Filter Replacement

Open the glove box. Remove the glove box stop on each side, then let the glove box hang down (see PASSENGER'S DASHBOARD UNDERCOVER REMOVAL/INSTALLATION ).
Remove the dust and pollen filter assembly (A) from the evaporator.
Fig 1: Identifying Dust And Pollen Filter Assembly
Remove the filter (A) from the housing (B), and replace the filter.
Fig 2: Identifying Filter And Housing
Install the filter in the reverse order of removal. Make sure that there is no air leaking out of the evaporator.

REMOVAL & INSTALLATION
NOTE: Manufacturer's terminology for this filter is dust and pollen filter.
CABIN AIR FILTER
Removal & Installation

Open the glove box. Remove the glove box stop (B) on each side, then let the glove box hang down. See Fig 3.
Fig 3: Locating Glove Box Stops
Remove the dust and pollen filter assembly (A) from the evaporator. See Fig 4.
Fig 4: Dust & Pollen Filter
Remove the filter (A) from the housing (B), and replace the filter. See Fig 5. Install the filter in the reverse order of removal. Make sure that there is no air leaking out of the evaporator.
Fig 5: Identifying Filter And Housing
If there was a maintenance reminder to replace the dust and pollen filter, reset the maintenance reminder, and this procedure is complete. Maintenance reminder can be reset using a factory scan tool, or equivalent aftermarket scan tool.

Dust and Pollen Filter Replacement

Open the glove box. Remove the glove box stop on each side, then let the glove box hang down (see PASSENGER'S DASHBOARD UNDERCOVER REMOVAL/INSTALLATION ).
Remove the dust and pollen filter assembly (A) from the evaporator.
Fig 1: Identifying Dust And Pollen Filter Assembly
Remove the filter (A) from the housing (B), and replace the filter.
Fig 2: Identifying Filter And Housing
Install the filter in the reverse order of removal. Make sure that there is no air leaking out of the evaporator.

REMOVAL & INSTALLATION
NOTE: Manufacturer's terminology for this filter is dust and pollen filter.
CABIN AIR FILTER
Removal & Installation

Open the glove box. Remove the glove box stop (B) on each side, then let the glove box hang down. See Fig 3.
Fig 3: Locating Glove Box Stops
Remove the dust and pollen filter assembly (A) from the evaporator. See Fig 4.
Fig 4: Dust & Pollen Filter
Remove the filter (A) from the housing (B), and replace the filter. See Fig 5. Install the filter in the reverse order of removal. Make sure that there is no air leaking out of the evaporator.
Fig 5: Identifying Filter And Housing
If there was a maintenance reminder to replace the dust and pollen filter, reset the maintenance reminder, and this procedure is complete. Maintenance reminder can be reset using a factory scan tool, or equivalent aftermarket scan tool.

Some background on that transmission service.

I brought it to that dealer for the 100k service. They replaced the transmission fluid, brake fluid, power steering fluid, and did an oil change. I went to this particular Honda dealer because the one closest to my house was $500 more expensive for the same services (minus a top end tune up).

Since I don't drive the car too often during the week I didn't notice the loss in mileage till I went on a longer trip. I took it to the Honda dealer nearest my house, explained to them the issue and recent service history. They found the transmission fluid had been overfilled by 4 qts so they drained, flushed, refilled and added trans fluid cleaner. It was an immediate difference. The car no longer hesitated to shift up to 5th and the mileage improved greatly.

Now, the car hesitates to shift to 5th when the motor is cold and has been sitting overnight in below freezing temps. So if I'm going 60mph at 2.2k RPM it won't shift up to 5th gear and drop to 1.6-1.7k RPM unless the motor is warm or has been running for more than 5 minutes.

The car doesn't shift hard or slip in an out of gears and anything that I thought was out of the norm I've been told by the dealer was normal for Hondas.

All air filters have been replaced within the last 5k so I'm pretty sure those are clear.

I guess I could check the trans fluid level and see if somehow that's off again, but I highly doubt it. I'm just concerned because I've never seen this much of a mileage drop off due to winter blends of gas.

To add to this, this vehicle has only been to Honda dealers since it was new for any service. So it's bizarre this is happening now.

the failure of the transmission not going into fifth gear property is most likely causing your fuel mileage, your fifth year on the transmission is your overdrive gear where you get all of your Fuel mileage. I would take it back to the dealer tell them after they service to transmission is having trouble going into fifth gear show him your evidence of your fuel mileage and see what they say.

I'll ask them about that this weekend when I go for an alignment. I noticed this morning when I let the car warm up for 3-4 mins before driving off, the transmission had no issues at all shifting up to 5th gear. I'm wondering if the cold weather is playing a role and if that's normal.

Either way, I'll ask Saturday.

ok, let me know what they say.

While at the dealer for an alignment, they checked / inspected the transmission. According to them, everything is fine. The fluid level is where it should be and the fluid is not dirty. It was taken for a lengthy test drive and everything was within spec.

The conclusion was that the delay in shifting to 5th was caused by the extreme cold we've been having lately combined with not letting the engine warm up and going straight to highway speeds.

Essentially, everything is okay.

I'm glad to hear that