why has my gas mileage gotten worse?

paulr

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I have a 1998 Honda Civic 5sp in good shape with regular maintenance, purchased new. Mileage in the first few years was maybe 30-31 hwy, 25 or so around town, not bad. When I took it in for the 60000 mile/4 year service they did stuff to it that increased the mileage by about 3 mpg both city and hwy, so I was very happy. Recently though it has gotten a lot worse, maybe 22 around town (these days I only use it for commuting, I haven't been out on the highway lately). What could cause this? At my last tune-up they said it was due for a wheel alignment (not that anything was visibly wrong, you're just supposed to have them every so often) but I haven't gotten around to scheduling it (just a matter of finding the time). Tire inflation is fine and tread wear looks even, so I figured the alignment isn't urgent, though I've been meaning to get it done. Could that have something to do with it?

Thanks for any ideas.
 

likeguymontag

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Try the Honda-Tech forums. There are some very knowledgable people who hang out there, and as internet car forums go, it's really quite good. Much less of the usual nonsense. Edit: at least in the Accord subforum. The Civic subforum might be full of ricers who flunked grammar. ;)
 
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Flying Turtle

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Don't know why your mileage has slipped, but I can't believe it's alignment related. They're always happy to relieve you of some bucks for alignments, but, like you said, the tire wear is even and inflation, so you shouldn't need one. Should be safe to wait on that.

Geoff
 

EngrPaul

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Gasoline has become less potent due to government regulations, including most recently mandatory ethanol. Has your commute habits changed? Shorter trips or more weight in your car will lead to poor ecomomy as well.
 

powernoodle

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Where I live, the government bureaucrats change the gasoline flavor twice a year, and I can notice that one flavor decreases my mpg by about 2, and then 6 months later it goes back up when the other gas blend is reinstituted. Maybe thats not your issue, but something to consider. Your prob could be anything from a dirty air filter to a brake caliper thats not releasing. Good luck.
 

vtunderground

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How many miles does your car have on it now? How old are the plugs/wires and air filter?

Keep in mind that you'll see lower fuel economy in the winter because the cold air is denser, so the ECU automatically adds more gas to maintain proper air/fuel ratio.
 

likeguymontag

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Keep in mind that you'll see lower fuel economy in the winter because the cold air is denser, so the ECU automatically adds more gas to maintain proper air/fuel ratio.

Probably has more to do with cold starts. The engine will run in open-loop mode until it reaches operating temperature, which of course takes longer when the block is 30°F rather than 80°F.

Remember that if you have more air and more fuel in the cylinder because the air is dense, you'll get more power in return, so you'll back off the throttle... giving the engine less air.
 

Hooked on Fenix

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I have found that gas stations are selling poor quality gas more often. My "09 Toyota Corolla got 30 mpg on the last tank. I added a Penzoil fuel additive and have averaged over 36 mpg on my current tank. The additive was around $1.30 at Walmart. If your dealer has been maintaining your car and covering the basics, you shouldn't have to worry about the tire pressure, air filter, oil level, spark plugs, fuel injectors, etc.
 

chmsam

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Get it checked out from a service shop (dealers can be way too expensive) and a second opinion on the car is as valid an option as getting one from another doctor for a medical problem (but usually a lot cheaper).

OK, some thoughts on some really, really basic stuff (you probably know it already but there are some who might not):

- When was your last oil and filter change? Some vehicles will see a drop in mpg and it's a simple fix you should be doing anyway.

- When was the last time you added fuel injector cleaner? Ditto for above. Castle Fireball Plus is good stuff but there are others. Follow the instructions on the bottle. Cheap preventive maintenance that actually works.

- Yes there are different gasoline blends for different seasons. That will change your mpg. If this is the cause, there is probably little to be done for the rest of the season but the change in the mpg should not be all that drastic.

- Are your tires inflated correctly? Check them when the tires are cold. Inflate according to the information on the inside of the door or door panel on the drivers door (there should be a sticker) or per the owners manual.

- If it really is an alignment problem your tires will start to show different patterns of wear. Most car owners manuals will show you what to look for but if not, it should be easy to find some pictures on the web.

- Also regarding alignment, the car will likely start to pull to one side or pick up a vibration even if only at certain speeds (examples would be between 40 and 45 or 60 to 65). Carefully drive down a flat, smooth, and straight road. When it is safe to do so, you might want to hold the steering wheel as lightly as possible for a few seconds to see if the car pulls to one side or the other. Some roads are "crowned" (have a slight incline at the middle of the road so that water drains off) and that will naturally cause the car to pull toward the shoulder to some degree so be aware of that. If the car has a vibration the easiest way to tell is to hold the steering wheel at the twelve o'clock position with one hand while holding onto the wheel normally with the other hand. With the hand that is at twelve o'clock, stick the index finger straight up and watch for it to wiggle. Any pulling or vibration should get attention and not just because of the loss of mileage. This is a big safety issue as well as causing increased tire wear as well as poor gas mileage.

- Check the oil and radiator for cross contamination. Water in the oil or oil in the coolant will make the engine run worse. Unfortunately these are signs of a blown head gasket. $$$

- Pull the spark plugs and inspect them. Do they all look OK? Are any of them too dark, too light, or oily? This is an easy diagnostic check for several different problems. A mechanic can easily tell what's going on or you can get a good repair manual and DIY.

- Bad plug wires can also lower mpg. When it is darker outside, pop the hood with the car running (outside -- not in the garage) and with a mist-like spray on a garden hose spray the wires. If you see any arcing or sparks, replace the spark plug wires and/or the spark plug boots (rubber covers over the plugs).

Again, this is old school, really basic stuff that a lot of people just don't get taught any longer. These are standard to-do items for any car owner and should help you in the direction for getting the problem fixed. If you were to do all of these checks, it should take about an hour and it is a lot cheaper to go to a mechanic if you already have an idea of what is going on. Cheap, fast, and easy!

Good luck.
 

Hooked on Fenix

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One thing to add is if your car has been recently Presmogged and Smogged, it may lower your mpg. During a presmog, a mechanic may adjust some things to lower the emissions to help your car pass smog. Unfortunetly, this results in poorer combustion in the engine and can basically counter a tune up. If you get a tune up, always get it after your car has been presmogged and not before.
 

paulr

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Thanks for all the advice everyone. Hmm, the car did get smogged last year, though I'm sure it passed without any problems. I think the cold starts are the likeliest explanation: I've been using the car almost completely for short distance commuting recently (3 miles each way), and the weather has been colder. But, I would have thought 22 mpg was terrible for this type of car even in the worst conditions.
 

Monocrom

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You did mention in your first post that you haven't been out on the highway as of late. That simple change in your driving habit could be the main reason why you're getting less MPG.

Short trips in & around town result in less MPG. Depending on the car, a lot less in some cases.
 

Big_Ed

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I think the cold starts are the likeliest explanation: I've been using the car almost completely for short distance commuting recently (3 miles each way), and the weather has been colder. But, I would have thought 22 mpg was terrible for this type of car even in the worst conditions.

My situation is virtually identical. I moved back in November to an apartment only 2 and a half miles from work. Previously it was around 10 miles or so. My average mileage has gone from about 25-26 mpg to around 17-18. The combined cold weather, and short city only trips killed my mileage. I have to warm up my car a little bit (maybe 5 minutes or so) in the morning to clear the fog/frost off the inside of the windshield. It doesn't even fully warm up by the time I get to work. That doesn't help mileage either. I'm sure it will get better when it warms up this spring.
 

likeguymontag

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[...] It doesn't even fully warm up by the time I get to work. That doesn't help mileage either. I'm sure it will get better when it warms up this spring.

Amusingly, it's also not good for your muffler. If the muffler doesn't heat up fully, it can't evaporate the water from the exhaust that condenses inside while it's cold. It's probably the one component of a car that lasts longer the more you drive.
 

Big_Ed

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Amusingly, it's also not good for your muffler. If the muffler doesn't heat up fully, it can't evaporate the water from the exhaust that condenses inside while it's cold. It's probably the one component of a car that lasts longer the more you drive.

True. But if I remember correctly, I think my car came from the factory with a stainless steel exhaust system. I'm not sure if that means the muffler is stainless steel too, though.
 

saabgoblin

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On a manual tranny? :thinking:
Can you say slipping clutch, that would definitely rob a few miles off of your commute. Shouldn't necessarily need one at 60000 but I live in San Francisco with 45degree hills that eat brakes and clutches for breakfast. Do you downshift to slow down, brake, or a combination of both, downshifting all the way back through all gears will shorten the lifespan of your clutch.

Just a thought after you cross off all of the little/easy fixes listed before and the short trip thing sticks out like a sore thumb especially if you are staying in lower gears.
 
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