Does anyone else notice that during the winter you get horrible gas mileage? I have a 98 Honda Civic DX and during the summer I got great gas mileage and now I get around 200-220 to the tank all city. I do let it warm up during the morning for about 15 mins and other days I'll take off without letting it warm up at all. Anyone have any ideas why its not lasting as it should?

 

It's normal to get significantly worse mileage in winter.

 

Alright, that's what I though but I wasn't 100% sure. Its definitely a significant decrease compared to any other time of the year.

 

Colder air means more dense oxygen molecules, which means more air coming into the cylinder, and to make up for more air, it needs more fuel to keep within a good A/F ratio.

 

15 minute warm ups is a bit much isn't it? Letting the car idle for that long can't be good for gas mileage. I'm no expert but I drive off after 1 min and got 406 to my last tank in a mix of city/highway.

Stock 96 dx 5-speed in cold DC area weather.

 

It may be but if you want to get technical Honda says no warm up period. If it starts you're supposed to drive it.

 

It is a bit long I would say but some days when the windshield is completely frosted I can't just take off and it takes a lil while for the heat to get going.

 

it is worse in the winter, but it shouldn't be that bad. i remote start my integra every morning and i still get high 20s mixed driving (300 or so to a tank)

 

Exactly.^

OP, think of it this way. That's 15 minutes of 0 mpg.

Two main reasons for lower mpg in winter.

1) It takes longer for the engine to reach normal operating temperature. During this longer warm up period, the ECU uses a predetermined rich fuel mix.

2) Summer and winter gasolines are made differently to overcome the reduced ability of liquid gas to produce gas vapor in cold temperatures. This necessary modification of gas will slightly reduce gas mileage.

And also do make sure the engine is tuned up.

 

It's not that long. I let the civic warm up for about half an hour in the mornings (I let it warm up while I take a shower and it takes me half an hour to get a shower and get dressed, otherwise I would only let it warm up for 15 minutes. Even at that when I left this morning I still had to scrape after having it idle for half an hour with the heat and defrost on, and the needle was still below the C. It just will not warm up at idle unless it sits there for about 45 minutes. If I just hope in it and drive it though It's up to temperature in less than 5 minutes. 15 minute idle times do cut into the mileage though.

 

I know this has been debated to death, but warm-up periods are not necessary. I just let it start, wait a few seconds for the oil to circulate, then go (slowly). You need to remember that other parts of the car also needs to "warm up". Like the transmission/diff for instance. If you have frost on your windows, just scrape it off.

Most winter mix gasolines are 10% ethanol, which burns cleaner, but your MPG takes a hit. Which kind of doesn't make sense to me, because that just means people will have to buy MORE gas and in the end, same amount of pollution is emitted. Maybe I'm not understanding something, though.

Also take into account that winter air is colder (denser). This means richer burning fuel (think of it like a CAI all-season long). More power, but less mileage.

 

The winter gas mix is less about emissions and more about producing a fuel that can efficiently atomize/vaporize under very cold conditions.

This is not an issue when the IAT sensor is working properly.

 

That doesn't always work very well. Sometimes the windows will start to fog up on the inside until you get heat. And if you get splashed or have to washer fluid it tends to freeze as soon as the wipers wipe (even with the -40 stuff.

 

I see. Thanks.

You can always turn the A/C on to get rid of the foggy windows. Has worked for me in the past...

 

1) warm up period
2) snow tires (more rolling resistance)
3) denser air


I notice my car, I can let it sit and run 10 mins, and it gets luke warm at best...drive it a minute and let the coolant flush around and it gets so hot I gotta crack the window.

warm-up periods aren't very beneficial as far as Im concerned

 

Again, a functioning IAT sensor eliminates this issue, right?

 

^ I thought it didnt matter, it would still affect it, however Ron---I think your one of the brightest guys on here, so Ill go with you!

 

The purpose of the IAT sensor is to measure the temperature of air entering the intake manifold. This way the ECU can adjust fuel injection to compensate for the higher density of cold air and the lower density of warm air.

 

Ron (and everyone else) I found this online---- I am in no way trying to argue with Ron, or anything, just opening this up for more discussion, and more importantly learning as we go. I by no means am an expert on this, just keeping our discussion rolling.

"Add to that the fact that gasoline doesn’t atomize and burn as well in cold temperatures; trace amounts of unburned fuel are left in the cylinder and evacuated with the exhaust. Yes, it’s a double-whammy. Not only does that unburned fuel equal lost power, it also substantially increases your vehicle’s emissions. But that’s not all—throw in heavy use of the heater, winter gas formulations and short trips to and fro, and it’s a recipe for pain at the pump."

check the article out under this -- couple points we didnt hit...like cars taking longer to reach optimum temp. Oil/fluids being thicker, yada yada yada.... interest read, I thought


It's Winter ... What's Happened to my Car's Fuel Economy?
Cold Weather Kills Fuel Mileage

Numb fingertips. Icy toes. Frosty windshields and frozen locks. Just when the cold blustery days might be getting you down, you notice that it’s taking more fuel to fill-up your vehicle. While it may be tempting to think that your calculator's batteries just need replacing, it’s time to face the cold, hard truth:

Winter conditions do cause a drop in fuel economy.

But wait—don’t make plans to move south yet. Grab your laptop and snuggle up by the fire or woodstove and take five for a few quick tips to keep more bucks in your wallet.
Old Man Winter’s Pinch

So, why exactly does colder weather throw a wrench at most vehicles’ regular fuel economy? Well, there are lots of reasons actually, but friction is a big one. While it's always an issue, cold weather increases friction on almost every front. Most vehicle fluids, from motor oil and transmission fluid to power steering fluid and differential gear oil, are thicker and more resistant to flowing when cold. Translation: Harder to pump, more work for the engine. Another less obvious source of friction is rolling resistance.

First of all, cold temperatures lower the pressure in your vehicle’s tires by 1 to 2 PSI for every 10 degrees that the temperature plummets. Secondly, when the weather turns foul, vehicles must work harder to push through snow and slush. Both of these conditions equal greater rolling resistance and more fuel used to cover the same distance. Add to that the fact that gasoline doesn’t atomize and burn as well in cold temperatures; trace amounts of unburned fuel are left in the cylinder and evacuated with the exhaust. Yes, it’s a double-whammy. Not only does that unburned fuel equal lost power, it also substantially increases your vehicle’s emissions. But that’s not all—throw in heavy use of the heater, winter gas formulations and short trips to and fro, and it’s a recipe for pain at the pump.
What’s Happening under that Hood

All vehicles have an optimum operating temperature, and the colder it is, the longer it takes to get there. While modern engines make very efficient use of the fuel mixture entering the engine, they rely upon the oxygen sensor to monitor the O2 content of the exhaust, as well as sensors for manifold pressure, mass air flow, throttle position, and coolant temperature, among others. All of this information is communicated to the vehicle’s computer that continually adjusts ignition and valve timing as well as fuel injector pulse width, to fine tune the amount of fuel delivered to each cylinder. This is done many times per second. But here’s the caveat—this engine-management system is only at tip-top efficiency when the engine is at full operating temperature. And when the mercury’s showing low, all vehicles require longer periods of time to reach that full operating temperature—and it’s in that warm-up period that efficiency is lost.

Add to that the common practice of making short trips (to minimize running to and fro in sub-zero temps and wind chills), and each time your vehicle cools down it has to come back up to optimal operating temperature. It all takes its toll.
Bottom Line: Here are the Tips

That’s right. We’re not here to bring on an even worse case of SAD (Seasonal Adjustment Disorder). We believe in being proactive and taking the bull by the horns … well, you get the idea. Anyway, here are some quick and easy ways to minimize the dip that your vehicle’s fuel mileage takes in the winter months:

Check your tire air pressure monthly—and keep it in the recommended range. Even if you don’t have an air compressor, you can invest in a tire-checking gauge and then swing in to the gas station. That’s five minutes that can save more than $5/month.

Plan your trips ahead of time—and do all your errands in one area at one time. By minimizing the stop-and-start, sporadic on-and-off operation of your vehicle in sub-zero temperatures, you’ll not only save time, you’ll minimize the amount of time your vehicle spends in warm-up mode.

Go easy on the accelerator. We can all take this advice. And it’s easily worth 1-2 mpg. Avoid jack rabbit starts and heavy motor-down mama driving. The guy in front of you will appreciate it—and the results will show up on your next fuel bill; plus, it might help prevent a wipe-out on black ice.

When possible, park your vehicle in a garage to keep it warmer, thereby shortening the time needed to reach full operating temperature.

Consider a block heater, an oil pan heating pad or a fuel heater for cars parked outside in frigid parts of the country; the initial expense will be recouped many times in added fuel efficiency.

 

So according to the article---your right, IAT (working correctly) will correct all that, however what they are saying is that until you reach operating temperature, it isn't working correctly. So lets say your warming your car up for 10 mins, and then you drive 5 mins before you reach operating temperature (both ways to and from work) so your running your vehicle for 30 mins a day and getting by default 0 mpg, or very bad.

I hope you agree, since that does make sense.

 

I did not read the entire article you posted, but where exactly does it say this^?

 

I don't have working A/C right now. But yes that does work well, also a lot of these cars didn't have A/C to start with. Or to put it another way, if you live in an area where you civic was originally equipped with A/C and it still works chances are you don't like in an area where winter driving is a major concern

 

Even with the IAT working, there is still more air coming in, and out, so the o2 sensor will notice this, and in turn the ecu will give more fuel to keep within a healthy A/F ratio.

The IAT is more for cold starts and engine warm up, the ECU compares ECT and IAT signals to give the right amount of fuel on cold starts and until warm.

 

The O2 sensor is ignored by the ECU when the engine is cold (open loop), so the O2 sensor does not affect the fuel trim until the engine is hot.

The ECU continues to use the IAT sensor signal even after the engine is hot.

 

Towards Ron--- (regarding optimum temp) however, in the article it says it has nothing to do with 02 sensor, which you have already negated. I dunno how viable this article is.