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My '03 LX Civic's MPG seems to be getting worse and worse. Never had a Civic (6th gen) give me less than 34 MPG in mixed driving and from what I know the 7th gen's MPG shouldn't be different yet my car is only getting me around 29 MPG even when half of the time I'm driving hwy, which I think really sucks especially that I live in Vancouver, BC, THE MOST EXPENSIVE place to buy gas in all of Canada (about $ 5.70 CaD/gallon -BIG RIP-OFF, just like everything else here). No codes and the car seems to be working fine. It's not my driving habits because I'm not hard on the car at all and try to keep the RPM under 3000 most of the time. Just read somewhere that it's a good idea to change the primary oxygen sensor as it can have a big impact on MPG, but again, no lights and no codes. I'm planning on changing the PCV too since I know it too can impact mileage and oil consumption. Any suggestions....other than the basic maintenance stuff and tire pressure, 'cause I know that's not the issue here ? I regularly use fuel injection cleaners. Oh, and does a bad cat. converter cause any codes to come on ?
Colin42, It's not that I think the cat is bad. I'm just wondering if a bad one would cause codes or CEL to come on, or is it possible to have a bad cat without any lights or codes ? But yeah there is a tiny hairline crack that's barely visible in the manifold but no noise and not much of a smell inside the car. The Civic ('00) I had before this one had a bigger and wider crack but that car had better mileage (34+ MPG/mixed drvng) and that car had a whole bunch of heavy tools in the trunk the whole time while this has an empty trunk.
ezone, I know cold temps and gas additives in winter affect MPG but no it's not cold here yet (Similar to WA State weather). I always keep track of my MPG and this car gave me better MPG in Feb than it's giving me now. Even in the middle of summer it never gave me more than 31 MPG even with 50% or more hwy driving. Not Civic-like.
No mods but it does have shitty old winter tires (I think Firestone). Old as in age but tread is actually really good (maybe 70% as the previous owner only drove the car like 6000 miles/year) but I think these tires are bad quality -from what I read- and noisy. Maybe they've hardened too much due to age and are causing too much friction but would that cause a loss of 5 miles/gal ?
I know that site quotes 29 MPG but there are other sites where owners' report getting more than 40 and even up to 50 MPG. And as I mentioned, I never had a Civic give me less than 34 MPG at worst but usually more than 36 or 37 MPG/mixed driving. Yes they were 6th gens but that shouldn't make a difference. This car has 100K miles on it while all the other ones I had had 160 K miles and above.
When I read the reviews on this car I see it over and over again - amazing gas mileage. 29 isn't amazing by any stretch. Most sites/owners report 30+ city driving, not mixed.
As you can see, 310civicEx got about 39 MPG -probably hwy- even with all the problems with his car (if we calculate the average US gas price to be around $2.85/gal. $60 is about 21.5 gal....).
I drive a 2012 Civic. It was rated at like 29/38 or something close to that.
It's got an instant economy display and an average economy display that I keep it reset with each tank fill up.
With the original LRR tires I could get over 50 MPG showing on the mileage display, but I had to drive it a certain way and it had to be all highway at consistent 50-55 mph, never slowing or stopping. As soon as I got to a town and stopped or turned the average numbers dropped fast. That was on a routine trip to my sisters place about 50 miles each way.
With 18" wheels and tires installed my average fuel economy dropped by 20% or more in some situations.
Nowadays when I travel on the interstate fast enough to keep up with traffic (sometimes 80-90 mph lol).......i can see UNDER 30 MPG average
ezone, I know stop and go driving will greatly affect fuel economy and here where I live driving is more stop than go but I had a bunch of other previous gen (6th) Civics to compare this one to but this is definitely the worst by far, and even on hwy MPG is crap.
I don't think there's any problem with wheels spinning freely and brakes aren't grabbing or anything. My suspicion is the crappy tires on the car especially that they're winter tires might be contributing to the bad MPG. One rear tire, or at least what I suspect is the tire is making too much noise that sounds like a bearing noise but the noise changes depending on the pavement and when the car was on the hoist (during an oil change) there was no play and no noise when the mechanic checked it. I know this isn't the most reliable way to check for a bad bearing but I'm wondering if a bad bearing can affect the mileage.
I would still like to know if a primary O2 sensor is something that I should consider changing -even though there is no CEL light and no codes. Could it be a bad injector ? Fuel filter/strainer ? F/A mixture thing ?
With the rip-off gas prices we're paying here -on top of all the other rip-offs here- I'd really like to get the most MPG out of my car and feel like I am driving a Civic.
One rear tire, or at least what I suspect is the tire is making too much noise
Choppy tread, probably eating the inboard edge (or more) of the tread
Bad alignment could cause fuel economy to drop, and eat up tires.
But the tires can get eaten up just from lack of care too, even with perfect alignment.
Next set of tires, look into LRR type. They may not be for everyone though. I'm sure they have some trade offs. Read reviews. Hell, look for reviews on the tires you have now.
I would still like to know if a primary O2 sensor is something that I should consider changing -even though there is no CEL light and no codes.
Sure, you can try it.
Also, check valve adjustment? Cam timing off a tooth?
Can you get straight gasoline there, no ethanol?
where I live driving is more stop than go but I had a bunch of other previous gen (6th) Civics to compare this one to but this is definitely the worst by far, and even on hwy MPG is crap.
Consider the 7th gen is heavier than a 6th gen, so it should need more fuel to move more weight from a stop..... I just google searched 'vehicle curb weight database'
The weird thing is that the tires look perfectly fine. No uneven wear anywhere on the tires. All look good actually. The previous owner was good with doing all the maintenance on this car as I have the records. It's not an alignment issue either as the car drives straight. They're a well known brand as I mentioned but like I said they had poor reviews especially on the noise problem. But I'm still not sure if the noise I have from one rear tires is actually the tire itself or the bearing. I think I'm going to put the tire on the front and see.
No. No ethanol-free gas here. Same as in the US. Hell, I wouldn't be surprised if the gas is mixed up with water here to try and make more money. But I'm sure it's not the ethanol because my other Civics still gave much better MPG.
Yes I realize the 7th gen is a heavier car but it is supposed to give the same MPG as the 6th, if not better from what I see on the net (from owners). And with my previous Civics I used to carry my tools (100+ lbs) in the trunk all the time but this one had the trunk almost completely empty for about 2 months, and still was getting less miles. Yes I realize as a heavier car it is going to use more gas from a stop but not 5 mpgs per gallon and like I said even on hwy it's not giving more than around 31 mpg.
It might need a valve adjustment 'cause I don't see it in the records. I'm not sure if it's a timing thing either but I'll try to get it checked next time (I don't have a timing gun myself).
Any way the primary O2 is bad even though no CEL is on. Are there any kinds of checks to see if the fuel/air mixture is all right ?
I can't stare at a tire and see noise unless the tread is absolutely horrible.
I have to spin a tire and watch the tread blocks as they go by. Any ripple or unevenness from block to block is a place noise can originate.
But I'm still not sure if the noise I have from one rear tires is actually the tire itself or the bearing.
Rotate the tires. If the noise moves to the front you know it was tires.
Any way the primary O2 is bad even though no CEL is on
How do you know this?
If it really is bad it can absolutely murder your gas mileage, especially if the computer keeps trying to add fuel because of it.
ezone, yeah I'm going to rotate the tires to see if the source of noise changes.
As for the O2 sensor, I'm not stating that it is bad. I'm asking if there's any way it can be bad -when there's no CEL on. I know the upstream sensor will cause the CEL to come on but don't know if it's the same case with the downstream. BTW, any recommended dwnstrm O2 brand ?
ezone, yeah I'm going to rotate the tires to see if the source of noise changes.
As for the O2 sensor, I'm not stating that it is bad. I'm asking if there's any way it can be bad -when there's no CEL on. I know the upstream sensor will cause the CEL to come on but don't know if it's the same case with the downstream. BTW, any recommended dwnstrm O2 brand ?
Thanks for taking the time to reply.
There are several codes possible for each of the individual O2 sensors.
Not all possible sensor related problems always cause codes to set. Then it sometimes becomes "No-code diagnostics."
Whatever brand the factory installed is what I like to see. As stated, see what yours has, it will be either NTK or DENSO.
i put a new o2 sensor on one side of my rustang and left the 100k mile sensor on the other side. below you can see how differently they perform. in my case factory calibration is as long as they switch from lean to rich once every 60 seconds, it is considered working. you can see in the graph below though that the new sensor switches from lean to rich 10x where the old o2 only switched once. it needs to cross a set value of .3v -.5v range for the computer to see it as functioning. so the computer says that old low lethargic line is fine. my logic is a bit updated, so if one side fails to switch within 15 seconds, the other o2 is used to calculate fuel trims on both sides.
...from another post i wrote as it's a PITA to load the datalog, filter out the temps under 180, make a custom chart, etc etc. -the yellow line is a bit washed out so you might need to squint a little.
just showing how a lazy sensor looks, not saying it's your issue. i'd blame the snow tires, check the air filter, etc. but i make signs, i'm not a mechanic so just my 2¢
Alright. I think it's worth it to replace the O2 sensor even if the one on the car might still be working, unless if I find out it's already been replaced. Even if it gives me an extra mile or two it will be worth it. I'm also going to replace the PCV valve. I don't think I'll be replacing the tires unless I find good used ones but I've read about people getting more MPG on tires with higher (than recommended) PSI. I won't go too much over but I'll see if that works.
I think the thermostat is working properly since the temp has always been where it should be since I bought the car. No fluctuations or anything regardless of the weather.
BTW, I had posted a question here when I first bought this car back in Feb and that's when and I was having a flashing CEL and getting codes (I think it was P0301, 02, 03 or 00) and the car would start choking or hesitating (at higher speeds) while the CEL was flashing but after a bottle of good fuel injector cleaner the problem never came back and all codes just disappeared, but I still wonder if there's still some kind of a problem with the fuel system. The spark plugs and coils were all fine.
I think I need to get rid of the M+S tires.
Do the O2 sensor sockets sold on Amazon work ? It seems a lot of people are having problems with them when it comes to the removal of the old O2 sensors.
They will work, you're in BC so you guys don't get rust issues that bad.or go to a parts store/canadian tire
You're doing the one right on top of the manifold right?
get the car warm, have your tools ready,
when you get home, pop the hood, unplug the o2 sensor, slap the socket on there and remove the sensor.
The hot exhaust will make removal easier. or with the car cold, hit it with some penetrating fluid, careful to only get on the threads.
Don't forget the antiseize for the new sensor
I'd replace the Primary O2 sensor with OEM Honda, Denso or NTK. PCV too. I'd also consider changing the spark plugs with OEM Honda NGKs only since you are at 100K miles. Tires at 35 PSI. New air filter too.
I think the thermostat is working properly since the temp has always been where it should be
Irrelevant, because the temp gauge is heavily buffered. The needle will stand in its normal position throughout about 50*F range of temp variation. (IIRC roughly 165-215*F does not change the needle position)
The only way to know for certain is with live data or an external monitor method.
Thanks, Colin. Yeah my understanding is that the O2 on top of the manifold is the one that affects the mileage and it's the one I should change to see if that helps with the MPG.
NDNV, Spark plugs aren't old (according to the car records from the previous owner) and they looked fine when I checked them a few months ago and I think they were NGK. Air filter was clean.
ezone, I might consider changing the thermostat but I'll wait and see if the O2 makes a difference first. I know colder operating temp or colder weather can affect mpg but this car never gave better mpg even when the temps here were 30+ (close to 90 F) this past summer.
I was on RockAuto looking at the O2 sensors and it seems they have different Denso/NTK (upstream) sensors for the same Civic model. Don't know which one to order.
I'm also looking for some brake pads, if someone can recommend a good basic ones.
did you figure out if you have a denso or ntk?
one you have that, go to the manufacturer's website and put in your car info, it will tell you what sensor to get.
i got mine from amazon, it was within a couple dollars and i got free shipping
Colin, not yet. I'm waiting for the socket to arrive. Tried to see if I could read the name on the O2 that's on the car but I don't think that's possible without removing it first.
09-24-2018
