Drop in MPG (09 Civic)

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harrad
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Drop in MPG (09 Civic)

Post by harrad » Sat Oct 13, 2018 6:24 am

I have a 2009 Civic with 90K miles. For the past 4 months I have noticed that the miles I get out of a tank of gas is has reduced quite noticeably. My drive habits have not changed. I have changed the air filter 2 months back and weekly check my tire pressures (32 psi or more in all tires). The car AC usage has come down a bit with moderating temperatures. A recent state mandated pollution inspection shows no issues.

I usually get 30-32 miles per gallon. It has now come to 22-23 miles per gallon. Any ideas.

pqwerty
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Re: Drop in MPG (09 Civic)

Post by pqwerty » Sat Oct 13, 2018 6:33 am

If they haven't been done recently I would start with plugs and coils. Just my opinion...

undertheradar
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Re: Drop in MPG (09 Civic)

Post by undertheradar » Sat Oct 13, 2018 6:40 am

Sounds like an Oxygen sensor if not plugs and coils.

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BoglePaul
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Re: Drop in MPG (09 Civic)

Post by BoglePaul » Sat Oct 13, 2018 6:47 am

Yes, sounds like it needs a tune-up (spark plugs).

livesoft
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Re: Drop in MPG (09 Civic)

Post by livesoft » Sat Oct 13, 2018 6:50 am

I am not awake this morning, so my initial post was irrelevant.
Last edited by livesoft on Sat Oct 13, 2018 7:00 am, edited 2 times in total.
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zeusrock1
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Re: Drop in MPG (09 Civic)

Post by zeusrock1 » Sat Oct 13, 2018 6:54 am

Maybe pcv valve?

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sunny_socal
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Re: Drop in MPG (09 Civic)

Post by sunny_socal » Sat Oct 13, 2018 7:20 am

- All the previously posted items
- Stuck brake (eg hand brake)
- Ignition coils
- Bad gas (avoid ethanol, it yields poor mpg)
- Dirty injectors (run a bottle of techron through the car)
- Needs valve adjustment?

Rupert
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Re: Drop in MPG (09 Civic)

Post by Rupert » Sat Oct 13, 2018 7:44 am

I vote ignition coils. I noticed a substantial drop in mpg in my Acura a year or so before a couple of ignition coils failed.

Nissanzx1
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Re: Drop in MPG (09 Civic)

Post by Nissanzx1 » Sat Oct 13, 2018 7:58 am

+1 On Techron fuel system treatment. Plugs are due if they haven't been done yet. Use OEM plugs. I'd clean the throttle body with throttle body cleaner.

Air filter, fuel filter. Make sure the basics are covered. Inspect the exhaust system for any damage (restriction of flow).

Run the car for any computer codes.

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ClevrChico
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Re: Drop in MPG (09 Civic)

Post by ClevrChico » Sat Oct 13, 2018 8:03 am

Try using top tier gasoline, because it contains 2x the detergents:

https://www.toptiergas.com/licensed-brands/

Tests show it may take 5k miles to clean out the carbon. I have similar behavior in my '09 Honda, and it seems to be gradually improving after using top tier gas. I believe CR recommends, so it's not just marketing.

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wander
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Re: Drop in MPG (09 Civic)

Post by wander » Sat Oct 13, 2018 8:10 am

You need to use the OBD reader to find out if there is any code. Autozone folks can help you for free. You don't want to replace an Oxygen sensor for no reason. If you are lucky, the ODB reader can find some fault code and you can go from there.

onourway
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Re: Drop in MPG (09 Civic)

Post by onourway » Sat Oct 13, 2018 8:13 am

I would take it to a good mechanic (hopefully you have one). Could be many things including those already mentioned here. Could be a stuck brake caliper, bad wheel bearings, the list goes on and on.

bubbadog
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Re: Drop in MPG (09 Civic)

Post by bubbadog » Sat Oct 13, 2018 9:03 am

You may want to check if one or more of the wheels is noticeably warmer than the others after a drive. If so, it might help determine if it is brake/ wheel bearing issue. A brake caliper dragging on the rotor will generate a lot of heat and it should be a noticeable difference in temperature.

inbox788
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Re: Drop in MPG (09 Civic)

Post by inbox788 » Sat Oct 13, 2018 6:43 pm

bubbadog wrote:
Sat Oct 13, 2018 9:03 am
You may want to check if one or more of the wheels is noticeably warmer than the others after a drive. If so, it might help determine if it is brake/ wheel bearing issue. A brake caliper dragging on the rotor will generate a lot of heat and it should be a noticeable difference in temperature.
Been looking for an excuse to get one of these temperature guns:

https://www.amazon.com/Etekcity-Lasergr ... 00837ZGRY/

I've seen similar ones go on sale for about $10.

So far, the only reason for me to use one is to check the outflow from the AC ducts, but with summer over, it won't be needed again for at least another 6-9 months.

You can always use your hands to get a feeling, but if you want to attach a number to it, and not just go by what's in your head, this would be another use. And if you had the toy, I'm sure you'd find other novel uses.

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baconavocado
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Re: Drop in MPG (09 Civic)

Post by baconavocado » Sat Oct 13, 2018 6:53 pm

That's a huge drop, it must be something major. As others have suggested, I would check the required maintenance schedule against the service history as a starting point. Make sure everything is being replaced when it needs to be replaced. 90K isn't that much for a Honda.

I usually notice a transient drop in mpg, 2-5 mpg, when I get new tires, but I've never seen a 10 mpg drop.

aqan
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Re: Drop in MPG (09 Civic)

Post by aqan » Sat Oct 13, 2018 7:01 pm

Those are some really good tips. Although I don’t have this issue but it’s a good knowledge that can come handy anytime. This is why I love this forum.

Smoke
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Re: Drop in MPG (09 Civic)

Post by Smoke » Sat Oct 13, 2018 7:12 pm

Have you noticed any performance issues?
Does it drive the same. uphills, accelerating etc etc?
I would expect some sort of noticeable performance issues dropping 30% in mpg.

Besides what was already mentioned...
Don't rule out gas siphoning, or a fuel leak, which would only leak under pressure, so no noticeable puddle under a car turned off.

maineminder
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Re: Drop in MPG (09 Civic)

Post by maineminder » Sat Oct 13, 2018 7:13 pm

Hard to diagnose. Most recently for me this was a stuck rear caliper. You've gotten quite a bit of good advice in previous posts.

I'm reminded of a previous 'Car Guys' episode where a young lady called in about her dad requiring her to log the amount of gas she bought and the mileage in a book in the glove compartment. This shows this sort of stuff.

After the car guys giving her a hard time after learning that he paid for the gas their advice was to start paying for your own gas if you don't like it! Great episode if you can catch it.

I ask my kids/wife to do the same :-)

Jack FFR1846
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Re: Drop in MPG (09 Civic)

Post by Jack FFR1846 » Sat Oct 13, 2018 7:38 pm

maineminder wrote:
Sat Oct 13, 2018 7:13 pm
Hard to diagnose. Most recently for me this was a stuck rear caliper. You've gotten quite a bit of good advice in previous posts.

I'm reminded of a previous 'Car Guys' episode where a young lady called in about her dad requiring her to log the amount of gas she bought and the mileage in a book in the glove compartment. This shows this sort of stuff.

After the car guys giving her a hard time after learning that he paid for the gas their advice was to start paying for your own gas if you don't like it! Great episode if you can catch it.

I ask my kids/wife to do the same :-)
This brings up a very good point. I don't know how many times I hearr people complain about the miles they get out of a tank with nothing but noticing how many miles have transpired since they last filled up. But they don't record the miles or gallons so actually have no real clue what the miles per gallon is that they're getting. If you are writing this all down with every fill up and have noticed the reduction consistent over many tanks, then I would agree that there's something in need of fixing. 22-23 is horrible for an 8th gen Civic. Even with a slush box. I can almost get that in my Wrangler.
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Smoke
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Re: Drop in MPG (09 Civic)

Post by Smoke » Sat Oct 13, 2018 10:27 pm

Something else to look at, the Thermostat.
If it is faulty it won't let the car get to full operating temp. it will run in open loop.
Very fuel inefficient. And my not be noticeable performance wise.

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whodidntante
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Re: Drop in MPG (09 Civic)

Post by whodidntante » Sat Oct 13, 2018 11:35 pm

I think ignition coils/plugs are unlikely. If you don't have good ignition you'll throw out unburned fuel. If you're throwing out that much unburned fuel it will occasionally burn in the exhaust pipe, and your catalytic converter will not live long. It tends to manifest as a misfire and it'll set a code, usually a flashing light as it's a catalyst damaging fault. However, you are coming up on the required replacement for the plugs, so at least do that. Ignition coils are not a maintenance schedule item, they are only replaced when failed unless you like burning money.

Measurement error (user or equipment). Miles driven / gallons put in to first click off is pretty close.
More stop and go miles or excessive idling
Theft of gas
Fuel leak
Parking brake stuck or dragging brake
Thermostat stuck open
Transmission
Low compression

It could also be a combination of minor factors.

harrad
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Re: Drop in MPG (09 Civic)

Post by harrad » Sun Oct 14, 2018 7:33 am

Thanks all for the fantastic replies especially if I read them in the "Car Talk" guys voice :wink:

I am hoping that it is not the ignition coils and spark plugs as I don't have any back firing or rough idling. The tire temperatures are not out of the ordinary and I don't see any issue braking at high/low speeds (no veering) so hopefully that rules out brake issues. No noise or change in ride comfort during riding at slow/highway speeds.

Diagnostics did not throw any any codes so hopefully that rules out any O2 sensor issues.

The operating temperatures have also been normal - the car warms up to the same point as usual (from the temperature dial at the dashboard).

No changes in acceleration and driving has been at Houston metro. So no hill driving.

I have been measuring the miles driven by the mileage trip meter in Civic - have been doing that since I bought the car. So I hope that gives consistent readings.

I have been filling at walmart for the past few months and am trying to instead use premium gas. That could be a possibility or it could be leak of gas. Any ideas on how I can rule this out. I do not see any puddle when the car is parked overnight or at the office.

Smoke
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Re: Drop in MPG (09 Civic)

Post by Smoke » Sun Oct 14, 2018 9:02 am

harrad wrote:
Sun Oct 14, 2018 7:33 am
Thanks all for the fantastic replies especially if I read them in the "Car Talk" guys voice :wink:

I am hoping that it is not the ignition coils and spark plugs as I don't have any back firing or rough idling. The tire temperatures are not out of the ordinary and I don't see any issue braking at high/low speeds (no veering) so hopefully that rules out brake issues. No noise or change in ride comfort during riding at slow/highway speeds.

Diagnostics did not throw any any codes so hopefully that rules out any O2 sensor issues.

The operating temperatures have also been normal - the car warms up to the same point as usual (from the temperature dial at the dashboard).

No changes in acceleration and driving has been at Houston metro. So no hill driving.

I have been measuring the miles driven by the mileage trip meter in Civic - have been doing that since I bought the car. So I hope that gives consistent readings.

I have been filling at walmart for the past few months and am trying to instead use premium gas. That could be a possibility or it could be leak of gas. Any ideas on how I can rule this out. I do not see any puddle when the car is parked overnight or at the office.
It could be a fuel leak only under pressure in the fuel lines, so parking over night may not show.
Have a good look under the car while it is running, perhaps place a long clean piece of cardboard under the car and run it for 15 min while also looking. Have you noticed any gas/fuel smell lately? After running the car and lifting the hood? Sniff around, Fuel injector O-rings may be leaking as well.

Oxygen sensors may be bad without throwing a code they wear out over mileage.
Usually needing replacement every 50k to 60k. depending on car and year.
When new they run lean and gradually run the engine richer and richer as the miles pile up.

A locking gas cap is under $20.

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pfrank
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Re: Drop in MPG (09 Civic)

Post by pfrank » Sun Oct 14, 2018 1:34 pm

I would start with the easy stuff first. First clean the air intake with SeaFoam Top Engine Cleaner. Then add SeaFoam Motor Treatment to the gas. That is simple DIY stuff. Plenty of YouTube videos on it. See what happens. If that doesn’t work, check to see if the brakes are okay (dragging emergency brake, stuck caliper, etc.). That can be DIY too if you are comfortable with taking off a tire. If that doesn’t work, bring it in to a mechanic for a tune up.

RudyS
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Re: Drop in MPG (09 Civic)

Post by RudyS » Sun Oct 14, 2018 3:40 pm

I've been driving since the late 50's. In the early years, one of my favorite remedies for issues that appear related to engine performance has been a can of GumOut. Usually worked well. Other brands would be good too. I would for sure try that first. But for the last few decades, the incidence of such issues has been minimal, if not actually zero.

And by the way, I did the keep a log book for at least 20 years. Never really learned much except that the gas mileage for a 53 Ford was about 16 mpg, and a 64 Chevelle not much better.

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