Want to improve highway mileage

[Ryland]

I tend to put on mostly highway miles, 100-160 miles at a time, and my mileage is still only 40-44mpg at it's very best, I know my 92 civic vx can do better! but I'm running out of ideas of things to check/tune/replace.
recent work:
New front bumper (old one was missing a chunk)
New throttle body.
New o2 sensor.
New 165/70 tires set at 44psi (max rated) front, 35 psi rear.
Synthetic 0w-30 engine oil, 10w30 synthetic motorcycle oil in tranny (had 0w 30 and a bearing was making noise)
a/c removed, grill to be blocked off as soon as the part shows up.
New cap, rotor, wires, ngk zfr5f-11 plugs.
New pcv valve, radiator cap, thermostat.
New larger oil filter to give more filter media/less restricion.
Removed and cleaned fuel injectors.
Replaced exaust and muffler with origonal fit aftermarket parts.
Replaced timing belt and water pump.

I normaly use 92-93 octane 100% gasoline.
I just ordered new oem suspension bushings as my front wheels have just a little play linked to the lower controle arm bushings.
I also ordered oem thermostat, I don't really trust the generic and I haven't been able to find a 192F thermostat, and don't want my fan coming on if it's not needed, and haven't been able to find proof/numbers that hotter is better, just theory so far.
I carry 200+ pounds of work related "stuff" with me alot of the time, but I try to go thru and remove extra unneeded weight when possible.
my compression is 180-185 accrose all cylenders (ideal is 185, 120psi is lowest alowable spec) and the engine seems to run smooth, you wouldn't know it has 220,000 miles on it.
I've thought about a belly pan, and I might make one, but as it is the front bumper's farring extends back nearly to the front axle.

So what can I do? I've been working on pushing this car for better mpg for year that I've owned it now and it's stayed at 40mpg for most of that year, creaping up a little but hardly noticable, it's not even reaching the epa mpg.

[thisisntjared]

i think it would benefit ever so slightly from a pcv catch can, just to help out with the octane of the air/fuel mixture. also cleaning all that gunk out of the intake manifold from all those miles will help raise the octane of the air/fuel mixture. those two go hand in hand

you already mentioned the belly pan which will definitely help. how is the alignment?

also i noticed two filters werent on your list: air filter and fuel filter, with 220k miles each could hinder the mpg. have they been replaced recently?

[Matt Timion]

I'm curious to know why you are using 92-93 octane. That engine is made for 87, so unless you are living 4000 feet below sea level I don't know why you'd need such high octane gas... unles you enjoy spending money.

I second jared's recommendation to get a new air filter and a new fuel filter. Don't forget to chagne the brass washers when you change that fuel filter. Trust me on that one.

Was it you that had the california VX, or was that someone else? If it's you, you really need to look into converting it to non-CA VX. It will take an extra wire and a new ECU. With that modification alone you'll break 50mpg (lean burn mode). If I'm thinking of someone else, please ignore me

At highway speeds your biggest mpg killers are due to aerodynamics. Work on that belly pan, and start brain-storming about rear wheel skirts. Maybe even getting some flat hubcaps would be a good idea.

Oh yeah, ditch the mudflaps.

[philmcneal]

try to maintain speed by pressing ever as little as possible on the pedal (usually this magic number is 40mph but on the highway try to maintain 50-55mph 60 is pushing it for your small engine)

but drafting works just be very careful. Sometimes it can be hardcore or it can be pretty damn sweet.

[krousdb]

Ryland, at what speed do you drive?

[SVOboy]

Just wondering, since I am about to swap injectors, what method did you go about the clean them out?

[krousdb]

Make sure you scrub your shizzles real good!

[SVOboy]

Okay, you lost me on that one!

[krousdb]

You know, the shizzie. It's the dealy bob that goes up and down in the injector.

[SVOboy]

Saturday is the day I wake up at 1 o'clock because I've only slept 20 hours during the week...help me out here.

[krousdb]

http://www.gassavers.org/forum_topic/gassavers_dictionary_of_technical_terminology.html

[Ryland]

I tend to drive 75mph, but the last few weeks I've taken a rout that requires me to stay around 60-65mph, going 75mph I'll get 39.5-40mpg going 65mph I'll top out around 44mpg, it's already close to a 3 hour drive every monday morning, so droping my speed by 10mph adds half an hour to my commute, or half an hour that I'm not sleeping or getting paid.

I changed the underhood fuel filter a year ago when I got the car... is there another filter? I should find out, at the same time I checked fuel presure, and it was within spec.
my air filter is a washable foam "turboflow" or something like that foam air filter, I've washed it twice, re-oiled it with foam filter oil, I've also put in a standerd paper filter for a tank or two of gas to make sure that wasn't draging me down.
when I replaced my throttle body a few months back (had a dead spot in the TPS) I sprayed some carb cleaner in the intake manifold, and also peeked in the injector holes in the intake manifold when I had the injectors out, to clean the injectors I removed them, scrubed off the carbon build up, soaked them in Sea Foam, and brushed them with a tooth brush untill they looked clean, I did not take them appart, and their internal resistance is within spec.
I have a 49 state civic vx, with a brand new 5 wire NGK sensor, o2 sensor wires are in good shape with a clean plug.
I had an alinement done a year ago and it still goes straight down the road, I plan to get an alinement done again after I replace some of the suspention bushings.
I'll look in to cleaning the intake manifold more.
I checked my valve clearnces today, last did it 15,000 miles ago, they were pretty good, 3 exaust valves were maybe .001" tight, one intake was just a little loose, they are now all exact, so we'll see if that helps any, but I think they were all close enough that it shouldn't matter.
I'm really hoping to get my highway mileage up, as this june we are planing to do a road trip out west, 3 people, 2000+ round trip, and every extra will help.

[JanGeo]

You need to reduce friction - add some oil additives. I don't go 75 in my xB but my 280 mile trip yesterday at night in rain got me 40.1 mpg there and 41.3 back doing 60-65 and try to get behind a bigger vehicle or a line of vehicles - if the line of vehicles is big enough they get the air moving your way and it greatly reduced drag. I was going 65mph and getting 55 mpg for a while behind a tractor trailer truck.

[krousdb]

Originally Posted by Ryland

I tend to drive 75mph, but the last few weeks I've taken a rout that requires me to stay around 60-65mph, going 75mph I'll get 39.5-40mpg going 65mph I'll top out around 44mpg, it's already close to a 3 hour drive every monday morning, so droping my speed by 10mph adds half an hour to my commute, or half an hour that I'm not sleeping or getting paid.

In the Prius on a warm day, 65 MPH = 55 MPG and 55 MPH = 65 MPG. I would rather go to bed 1/2 hour early and leave for work 1/2 hour early for one day a week than to give away 10 MPG. But thats just me. I am a nut!

[n0rt0npr0]

Ryland,

Brake Drag could be a factor. Just do a search on the site for more info into that.

Otherwise the aero mods are worth some research.

[rh77]

For me, driving at 60 mph or under worked wonders for the highway MPG. I know it sucks getting passed by everyone, but I get 40+ on the highway at 57 mph and about 20-30 MPG at 80 mph -- it's just the simple physics of wind resistance vs. power. I just need to get the city driving figured out because that's really killing my mileage right now.

RH77

[Compaq888]

Originally Posted by n0rt0npr0

Otherwise the aero mods are worth some research.

BINGO!!!!!!!!!!!!!!!!!!!!!!!!!!

we have a winner. It doesn't matter how fast you're going on the freeway, aero stuff that's done right always helps.

[n0rt0npr0]

Originally Posted by rh77

For me, driving at 60 mph or under worked wonders for the highway MPG. I know it sucks getting passed by everyone, but I get 40+ on the highway at 57 mph and about 20-30 MPG at 80 mph -- it's just the simple physics of wind resistance vs. power. I just need to get the city driving figured out because that's really killing my mileage right now.

RH77

Some sweet info...
You could potentially log all speeds and create your own specific non-linear graph. Lucky OBDII people!