My gas mileage is 10mpg less than it should be

[llmercll]

Hello everyone,

I have a 2001 Honda Civic HX (manual transaxle) in good shape, with a strong engine. I'm here because my gas mileage is not very good. I'm getting about 24.5 MPG when almost everyone website says I should be getting 10mpg more than that. My miles are split between highway, country road, and city.

http://www.fueleconomy.gov/feg/noframes/16514.shtml

According to this I should be getting even more if it's all city! I don't drive rough at all, and go 70 on highway and 50 on country roads. I'm a smooth accelerator and breaker.

Any ideas what's going on and what I can do to improve mileage?

thanks for reading!

 

[SwampSurvivor]

I'd look at the condition of the following:
- Tune Up Hardware (plugs, wires, air filter, maf sensor)
- Alignment (can easily take away mileage)
- Dragging brakes
- Bad wheel bearings.

 

[SatinSilver]

How are you going about calculating your mileage? Make sure tires are full of air, to the recommended psi. Also try not to be a smooth breaker. Otherwise, you'll be fixing things all the time.

 

[JHZR2]

Not trying to be mean, but Ive generally found it to be user error, either in maintenance and/or driving style.

Winter gas blends can hurt too, but not sure if that is an issue yet.

Have any check engine lights? Is everything maintained? What kind of tires do you run?

 

[ThirdeYe]

Originally Posted By: Miller88
I'd look at the condition of the following:
- Tune Up Hardware (plugs, wires, air filter, maf sensor)
- Alignment (can easily take away mileage)
- Dragging brakes
- Bad wheel bearings.


These are all good suggestions. Might I add:
-Tire pressure
-Oil viscosity
-Potential fuel leak/evaporation
-Oxygen sensor(s)
-Driving habits

The biggest one for me is my last suggestion. I can easily lose 10 mpg by driving spiritedly.

 

[Quattro Pete]

Originally Posted By: llmercll
I'm a smooth [..] breaker.


Oh yeah, what have you broken smoothly? Whenever I break stuff, it's usually with a big bang.

Seriously though, I will restate the previous poster's question: are you sure your calculations are correct?

 

[Danno]

Add "plugged cat convertor" to the checklist as well.

 

[SevenBizzos]

That website is pretty funny. It says my Prelude should be getting 19/24 and I've always scored 27.5-29 and an occasional 30+ when I was trying. That's with blended fuel too.

As for your issue, I'd think something isn't firing right. I think you'd notice the backpressure difference from a plugged converter, but could certainly be wrong..

 

[ThirdeYe]

Originally Posted By: SevenBizzos
That website is pretty funny. It says my Prelude should be getting 19/24 and I've always scored 27.5-29 and an occasional 30+ when I was trying. That's with blended fuel too.

As for your issue, I'd think something isn't firing right. I think you'd notice the backpressure difference from a plugged converter, but could certainly be wrong..


I'd think you'd notice something wrong if the cat was plugged, too...

I used to consistently get above EPA estimates in my car when I did more highway driving. I've gotten as high as 36 in my car, when it's only rated for 29.

 

[davebarnum]

Originally Posted By: llmercll
Hello everyone,

I have a 2001 Honda Civic HX (manual transaxle)...



BIG variable right there. My first advice would be to review your shift points. And yeah, driving habits.

 

[llmercll]

thanks for the fast replies, you guys are the best!

No check engine light. Alignment is ok (doesn't pull to the side much). oil viscosity is manufacturer recommended 5w-20.

The engine purrs, and even though it's 13 years old used oil still comes out pretty clean (not super black). I think the transmission has a worn input bearing though, since I hear some chattering when i accelerate in low gears, and get some slight "grinding" at idle when the clutch is engaged (it's silent when I push it in).

I don't get any acceleration hiccups, or anything bad for that matter. the car runs great. I haven't checked spark plugs or wires, or air filter. I don't know how to tell if wheel bearings are bad or if my brakes are dragging (they seem fine though). My shift point is around 2.5k rpm

maybe the fuel injectors are dirty?

 

[bepperb]

We had an 03 Civic EX manual and I drove it pretty hard and don't think I ever had a tank below 30mpg in mixed city/highway.

Can you jack the wheels up and make sure all four spin smoothly (no bad wheel bearing, no dragging brakes... etc)? That and a tune up and see. Has the timing belt been replaced, any chance it's one tooth off?

 

[Merkava_4]

You might be at the beginnings of a plugged up catalytic converter. Pull the oxygen sensor
and screw in a back pressure gauge. You should not have more than 2 PSI back pressure.

 

[cchase]

Set the car on a level surface, disengage the driveline, take the parking brake off, and see how easy it is to roll. If you can't roll it, I'd start jacking it up one corner at a time and spinning the wheel in question to make sure you don't have a dragging brake.

 

[eljefino]

Originally Posted By: cchase
Set the car on a level surface, disengage the driveline, take the parking brake off, and see how easy it is to roll. If you can't roll it, I'd start jacking it up one corner at a time and spinning the wheel in question to make sure you don't have a dragging brake.


Yeah this!

Also find a slight hill then drive up it and throw it in neutral. Let it roll to a stop then start rolling backwards. If there's drag you'll feel it on the reversal.

 

[L_Sludger]

That's friggin miserable mileage. Maybe you have an issue with your oxygen sensor or something. Something's really wrong. I'd kvetch if my Insights (70mpg nominal) were getting 10mpg less. Your car is in Chevy Silverado V8 truck territory. Hope you can figure it out.

 

[artificialist]

Does this car use a MAF? If it does, it may be inaccurate, but not inaccurate enough to trigger a warning light or error code.

Does the engine coolant temp sensor work correctly, and does the thermostat open at the specified temperature? If that isn't happening, your car will run in open loop mode, and never have good MPG. This happened to a Honda Accord I had many years ago.

 

[hattaresguy]

How are you calculating the mileage and is your odometer even correct? Verify the odometer with a GPS.

Mileage over a tank doesn't really mean much, you need to calculate the mileage every single tank to see trends developing.

For example with my work truck over the past 80k miles I have averaged 14.5-15.7 around town and in the 19 range on the highway. But my out outliers have been as low as 11 and as high as 20.5.

 

[llmercll]

I checked the car by rolling it today. It rolls, but does take a bit of effort. I assume thats normal since it's a 2000lb vehicle.

I added some air to my tires today, they weren't very low though (honda only recommended 30psi)

 

[eljefino]

So you pushed it by hand, did it creep to a stop or "just stop"?

This is hard to describe online, but I think you have dragging brakes.

Try pushing another car, the same weight.

Do both when they're warm so the wheel bearing grease is less viscous.