Since last fall, late October, I’ve noticed a mileage drop in my Accord (4 cyl/auto). Normally when winter blend arrives, I get around 27 mpg but now I’m getting less than 24 mpg. A scan shows no codes or pending codes. The air filter and spark plugs were changed in August and the MAF sensor was cleaned. Tire pressure is good and brakes are not dragging. In all the years I’ve owned this car, I’ve never seen MPG this low. Anyone have an idea about what could be causing it?
What method are you using to determine your mileage?
And where, roughly, do you live? It was crazy cold here for a few weeks, and my gas mileage suffered as a result.
Also, are you filling the car up at the same gas station every time?
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Year? Miles?
I use the same method I’ve always used: Miles driven divided by gallons in a fill up. I’m in NE Ohio and this problem has been ongoing even when the temp has been normal (for winter here).
This is an '04 model with almost 165k on it.
At 165,000 niles, perhaps the compression isn’t what it used to be. You might want to check your odometer with a measured mile. Did you replace your tires recently and, if so, are the new tires the same size as what Honda specifies? I once owned an AMC Javelin that came with 6.95 X 14 tires. I found some good used 7.75 X 14 tires and put them on. All was well until we took a road trip. When I stopped for gas, my mileage was 7 mpg less than what it normally was. The engine took a quart of oil which it had never done before. When I was running an indicated 70 mph on the speedometer, the engine seemed noisy and the car didn’t have much acceleration above an indicated 70 mph. We were making a trip from Indiana to Nebraska. My wife, who likes to calculations figured out when we crossed over into Nebraska that we had averaged 82 mph across Iowa. I was running the little 232 six in the Javelin practically wide open. I learned to transpose the indicated speed on the speedometer to the actual speed and we calculated a constant to multiply the miles indicated on the odometer to actual miles traveled.
When did you change the spark plugs?
A drop of over three MPG from compression loss? It would have to drop a few rings for that much loss. No new tires recently.
Plugs were changed in August and mileage was consistent with previous checks up until fall.
Tires can make a rather big difference in MPG’s even in the correct size, even properly inflated.
Also, everything that rotates has 165K miles on it. Normally a car’s MPG’s improve with run-in miles. Yours is past run-in and deep into wear-out miles. There are many, many things that can affect the MPG of the car. A sudden drop usually has a cause and can be a cause the engine computer can’t measure - so no CEL.
Does the engine take a long time to warm up? A failing thermostat will cause that symptom and drop your MPG’s like a rock.
It is a possible transmission problem. Has the fluid ever been changed? Maybe you should drop the trans pan and take a look inside for metal bits. It takes fuel to tear up the inside of the trans. If it looks OK, change the filter and fluid while you are there. Check drive axles.
Carefully inspect engine oil for metal flakes. Run a compression test on the engine or better a leak-down test. Check all the injectors - idle the engine and unplug the injectors one at a time and see the rpm drop. It might be time to replace the coils, plugs and wires.
The list can be endless but if you want to find the “red X” or cause, it will take time and effort.
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No it wouldn’t take anywhere near that much. 3 MPG from 27 is 11% One compression ring would cause that in a 4 cylinder.
I have been getting around 29 MPG, measured the same way as you do in my 14 Subaru Legacy, but this winter it has dropped to around 26, even lower in some weeks of extreme cold. I think most people are getting worse than normal fuel economy this winter.
Normal warmup time and the trans fluid is changed every 30k miles. I’m meticulous about care with the car and my previous two Accords went well over 200k miles without this type of problem or any serious problems. When I changed the plugs, the old ones showed normal color. I did add Techron fuel injector cleaner last week. I’ll have to wait for a week or two to see it that makes a difference.
Best I can tell you is to keep an eye on your MPG’s and see if it returns to normal levels for your car. If it doesn’t, you have some investigating to do.
Or not. If something is failing, you’ll find it fairly soon. If it is just age, even if you find it, would you spend money to “refresh” it to get your 11% back?
There are many reasons the MPG drops in cold weather.
http://www.fueleconomy.gov/feg/coldweather.shtml
Tester
I agree. Worst case, I’ll have to wait until summer blend comes back.
That article shows some good points but I’ve used this car for the past 14 winters and never seen mileage this low. Thanks for the help.
One common reason for unexplained lowered mpg is a faulty thermostat. If it distorts and leaks even a little, it will lower the operating temperature. Even a slightly reduced temperature will noticeably lower mpg. If the thermostat has never been replaced, that would be my first guess. I had to replace the thermostat on my Corolla a year or so ago for that reason. When I removed it, very clear it had distorted from the corrosive and thermal effects of being in the engine doing its job for a long time, and no longer presenting an effective seal to regulate the coolant temperature.
I live in Western NY near Buffalo, I just got an email from National Grid that this winter has been 13 % colder than normal.
If I were you , I wouldn’t do anything until summer.
If you want to be really happy about your gas mileage, do like most people do, only check it on a summer road trip, but brag about it all year 
on such a big mileage, if air/fuel ratio sensor (this is also called an “upstream oxygen sensor”) starts to deteriorate, it will often err on the lean side, leading to ECU over-correcting into running rich, resulting in higher fuel consumption
if that sensor was never replaced, it might be one of ideas to entertain