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Story: I recently bought a 2013 Civic and during my first oil change I noticed that the person before me had completely removed the big splash guard that goes underneath the engine (a big plastic sheet-like piece that runs the width of the car and from the front fender to about 1/3rd of the way to the rear; it has 2 metal sheets attached to it).

I eventually tracked one down at a junk yard and saw an immediate difference of 1-2 MPG in every kind of driving condition. My city-only trios went from 26 to 28, mixed went from 36 to 37 or 38 (it varied). And once a month I take a long drive upstate where I just set the cruise to 65 the whole time; I used to max out at 47 MPG, now I'm maxing out at 48.

Anyways, I know sometimes people lose these splash guards for whatever reason, but make sure you keep yours on, as it's well worth having.
 

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They are the underbody spoiler air diffuser and they smooth out the underside so it's less resistance aerodynamically. Some remove them due to braces being added and they are unable to fit with them installed without being modified. I'll be in that boat for the rear one when I install the Ultra Racing rear subframe brace.
 

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Good post. Honda spent alot of money designing that piece and testing it in wind tunnels and is a part of the car just like a door handle or windshield wiper and yes it absolutely helps MPG especially long highway drives.
 

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Good post. Honda spent alot of money designing that piece and testing it in wind tunnels and is a part of the car just like a door handle or windshield wiper and yes it absolutely helps MPG especially long highway drives.
Agree, but I have to wonder what is worse:
a front engine under cover plate that is missing
or
a front engine under cover plate that is mangled or detached in the front

How some here are getting 26 MPG or more in town continues to baffle me.
My '12 sedan is doing good to get 23. something under these conditions, last tank it got 22.1 MPG.
In town trips for me rarely are faster than 35 mph, or longer (one way) than 3 miles.
 

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Story: I recently bought a 2013 Civic and during my first oil change I noticed that the person before me had completely removed the big splash guard that goes underneath the engine (a big plastic sheet-like piece that runs the width of the car and from the front fender to about 1/3rd of the way to the rear; it has 2 metal sheets attached to it).

I eventually tracked one down at a junk yard and saw an immediate difference of 1-2 MPG in every kind of driving condition. My city-only trios went from 26 to 28, mixed went from 36 to 37 or 38 (it varied). And once a month I take a long drive upstate where I just set the cruise to 65 the whole time; I used to max out at 47 MPG, now I'm maxing out at 48.

Anyways, I know sometimes people lose these splash guards for whatever reason, but make sure you keep yours on, as it's well worth having.
They are the underbody spoiler air diffuser and they smooth out the underside so it's less resistance aerodynamically. Some remove them due to braces being added and they are unable to fit with them installed without being modified. I'll be in that boat for the rear one when I install the Ultra Racing rear subframe brace.
Agree, but I have to wonder what is worse:
a front engine under cover plate that is missing
or
a front engine under cover plate that is mangled or detached in the front

How some here are getting 26 MPG or more in town continues to baffle me.
My '12 sedan is doing good to get 23. something under these conditions, last tank it got 22.1 MPG.
In town trips for me rarely are faster than 35 mph, or longer (one way) than 3 miles.

i think op's missing the front so he add it back...

the front under body panel is only available for the r18 civic, si don't have it, i did install the front underbody panel on my car and i did not see any improvement, we also remove the rear one and i also don't see any negative effect without the rear under body panel..

the only aerodynamic honda part that made a huge difference (on any of my car) will be my honda accord plug-in factory 17" wheels with aerocover... my r18 jump from 26mpg to 36mgp, i usually swap wheels once every 6 months~1 year, but this forged factory wheel perform so well that i have been using it for 2 years straight.

my r18 with 300mm brake kit never fade anymore (stock is 272mm), when 18-wheeler next to me at high speed, my car do not drag into it anymore, it is the one of the best wheels i have ever experience since since 1986. even my 13lbs forged joustmeister don't perform the way oem plug-in wheels does...
 

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Agree, but I have to wonder what is worse:
a front engine under cover plate that is missing
or
a front engine under cover plate that is mangled or detached in the front

How some here are getting 26 MPG or more in town continues to baffle me.
My '12 sedan is doing good to get 23. something under these conditions, last tank it got 22.1 MPG.
In town trips for me rarely are faster than 35 mph, or longer (one way) than 3 miles.
I'm supercharged now, and still somehow manage 26.5MPG. That's mainly "normal" driving, with probably 7-8 WOT pulls to redline in 3rd gear.

Mine will probably worsen though, when I finish the tuning process with Vit.
 

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How some here are getting 26 MPG or more in town continues to baffle me.
My '12 sedan is doing good to get 23. something under these conditions, last tank it got 22.1 MPG.
In town trips for me rarely are faster than 35 mph, or longer (one way) than 3 miles.
My '12 LX 5AT averaged 23 to 24 in city (stop-and-go) driving most of the time. I got a high of 42.5 on a highway trip once. Usual highway was about 36.

My '15 LX 5MT regularly gets 28 city/33 highway under the same conditions. The only difference is the transmission.

Is yours an Si, Teeps?
 

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Agree, but I have to wonder what is worse:
a front engine under cover plate that is missing
or
a front engine under cover plate that is mangled or detached in the front

How some here are getting 26 MPG or more in town continues to baffle me.
My '12 sedan is doing good to get 23. something under these conditions, last tank it got 22.1 MPG.
In town trips for me rarely are faster than 35 mph, or longer (one way) than 3 miles.
Yeah I only get like 22-24 somewhere in btwn. I blame the traffic.
 

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Yeah I only get like 22-24 somewhere in btwn. I blame the traffic.
I get around 20-21 MPG in the city as well...its horrible and its also why if Im just going a few blocks over from my building and I can help it to leave the car at home I do so and instead just walk...I try my best to only use my car when I have to go out of the city to visit family or old friends who live outside of the city as well but that's not always possible because it's murder walking home with heavy grocery bags.
 

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My undercarriage panels were collecting snow and ice and ended up filling and dragging on the ground everywhere I went. They had to come off. Just my $.02
 

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Agree, but I have to wonder what is worse:
a front engine under cover plate that is missing
or
a front engine under cover plate that is mangled or detached in the front

How some here are getting 26 MPG or more in town continues to baffle me.
My '12 sedan is doing good to get 23. something under these conditions, last tank it got 22.1 MPG.
In town trips for me rarely are faster than 35 mph, or longer (one way) than 3 miles.
This won't help your feelings but the very least I get in town is 32mpg and more commonly 34 to 35mpg. in a 2012 stock automatic EX. I do anticipate stop lights and just let it glide to them if they're red. Other than that I drive about 5mpg over the limit and more. I also use mid-grade fuel. Regular gas is not as good as it used to be IMHO. There's a definite difference in the way mine runs on mid-grade and premium. I seldom use premium because I can't tell that it makes a difference in anything over mid-grade. Other than that, I just keep my foot out of it. I get 42-43 on the highway doing 75mph. I do run it up to 6000rpm or above now and then just to keep the crap out of it.

I also let the car glide when I know a stop is coming. It uses no gas when gliding. A Civic will coast a long way with foot off the gas due to the aerodynamics being so good. Look at it from the side and it's shaped well. Also, the under-plates help reduce turbulence under the car. All of this helps with mileage. I also anticipate hills. When going down hill I may let it build up speed well above the speed limit so it will glide most of the way up the next hill thus using the throttle very little going uphill. In heavy traffic, I take it off ECON because that's where I want power when changing lanes or when I need to dodge the stupid drivers. Otherwise, I keep it in ECON mode which does work for me. Hope maybe this gives you some new insight, Teeps. You sure do help a lot of people here and it's appreciated by me at least. ; )
 

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After changing my cvt fluid recently, i noticed that my aluminum under body cover was bent upwards (imagine a transmission tunnel shape). it was also missing one of the screws that hold in place. when i went to dealer to get the screw, they showed me a new underbody pan...and it was flat. guess i ran over something that dented it. glad it was there! also, with it having to be removed to change the oil filter...i imagined that Honda decided this was needed for some reason or another - so, i kind of flattened it out and reattached it - albeit still one screw short. dealer couldn't figure out what screw i needed by the diagrams. he kept bringing me the plastic ones.

btw, i get about 31 in town, but i anticipate stops and such and drive similarly to R/C above (never thought i would ever make a statement like that!)
 

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I get around 20-21 MPG in the city as well...its horrible and its also why if Im just going a few blocks over from my building and I can help it to leave the car at home I do so and instead just walk...I try my best to only use my car when I have to go out of the city to visit family or old friends who live outside of the city as well but that's not always possible because it's murder walking home with heavy grocery bags.
must be a socal thing :wavey:
when I drove down to san diego i got like 31mpg in my SI so its definitely possible to get decent mpg. Just in normal day to day driving, traffic down here is just brutal at times which definitely kills your mpg.
 

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This won't help your feelings but the very least I get in town is 32mpg and more commonly 34 to 35mpg.
Nothing to "feel" about it, it is, what it is.
The traffic and short one way trips; most of which are from a cold start condition, certainly contribute to my car's lower MPG that your's
The other socal guys/gals here report similar MPG to what I am seeing, with my '12 EX sedan a/t.
I've done octane tests over several fill ups and never saw a consistent difference in MPG.
What does bump the MPG is when the car gets on the freeway. One 50 mile round trip will bump the MPG 3 to 4 MPG, for that tank.

What is painful, is the paying for the gas.
 
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