Very Low Gas Milage In Cold Weather. Why??

[Infantrylowlife]

I noticed today that in like 15 degrees my car get crapy mpg like I only got 280 miles on a full tank when i normaly would get like 370 to a tank???????

 

[Mocoso]

Well I woudnt expect it to get 30% less so I would re-check your numbers but (My total WAG theory based on my limited and possible wrong knowledge))one possible reason could be that colder air is denser = more air into the engine

In order to keep the right air/fuel mixture (AFM) correct (so it wont over lean)more fuel would need to be added OR the amount of air being let in would need to be lowered

I thought our ECU would actually manage both depending on the power being requested by your foot which would mean that if you werent stomping on it more the ECU should be able to mantain the AFM by adjusting the air rather than increasing the fuel....

Then again it could just be somewhat dumber and assume you would want the extra power and just give it more fuel... but that would mean that people in Colorado would be getting much better fuel economy than those in Death Valley and that isnt the case (not the 30% you are talking about) lot more experts here in the forum that can explain this better -

 

[schmitty]

I have always had poor gas mileage in the winter. I assume it had to due with th colder air being more dense. It could also be that you are running the fans and idling more.

 

[ForceFed]

It has to do with most people starting their car and letting it idle to warm up and MAINLY with running the Defrost alot...The defrost mode actually runs the AC compressor and results in lower milage.

 

[autoxes]

threadjack
wait, so when I remove my AC system for autocross this year, it takes away defrost capabilities?

 

[ForceFed]

threadjack
wait, so when I remove my AC system for autocross this year, it takes away defrost capabilities?

It removes the moisture removing ability which is the heart of a defrost system.
The heat will dry and defrost the window on its own...just not as efficiently.

 

[terbow]

dont forget the gas recipe changes in the winter too. that can change your mpg. the summer blend gives off less smog but its not good for starting in the winter.

 

[sahtt57]

There can be several reasons for poorer fuel mileage during the winter months. I used forum dig poor fuel mileage Additional idling and inadaquate ECU adjustments can be to blame, but the more avoidable attributes to poor gas mileage are typically under inflated tires because of the colder weather and the heater, which can use a ton of energy to power.

 

[Hirudin]

It has to do with most people starting their car and letting it idle to warm up and MAINLY with running the Defrost alot...The defrost mode actually runs the AC compressor and results in lower milage.

I don't think I'm alone here: I run my car with the A/C on at virtually all times in the summer.

 

[AllLostThings]

Do you have a normal Mazda 3? I tend to get about 270-280 out of a tank of gas on average with my Speed3.

 

[aaronc7]

yeah this cold weather sucks here too in FL...high of 82 today...

 

[Infantrylowlife]

Ok I found out what the problem was. Its my IMRC sensor its gets stuck closed on our motors in very cold temps there is a recal i think for it but its happening more on the cx7's and ppl are reporting 16 mpg with the bad sensor. After the new one with the stronger spring is installed ppl can tell a big diffrence in power and mgp. All the IMRC ( Intake manifold runner control) dose is close off ports for starting and for more power at lower rpms and usualy makes the ceck engine light come on too.

 

[BluMicaR]

Hey, a little off topic, kinda...

When I have the heat on and temp is, say, 78*, and I hit 'auto' the "A/C" button comes on and the fan kicks up, as if it was auto for hot weather... WTF is goin' on? I thought maybe defrost would come on, but why is A/C coming on when the heat is on???

 

[Hirudin]

BluMicaR, that happens in my car too... When I notice it I hit the A/C button to turn it off.

 

[robin2660]

Ok I found out what the problem was. Its my IMRC sensor its gets stuck closed on our motors in very cold temps there is a recal i think for it but its happening more on the cx7's and ppl are reporting 16 mpg with the bad sensor. After the new one with the stronger spring is installed ppl can tell a big diffrence in power and mgp. All the IMRC ( Intake manifold runner control) dose is close off ports for starting and for more power at lower rpms and usualy makes the ceck engine light come on too.

The answer is a couple posts up ....

In case you don't find it, AC lowers the humidity, which reduces fogging. It is a built-in feature. On older cars, it is a common recommendation to turn on the AC with the heater for just that purpose. I just crack my windows a little bit.

 

[Infantrylowlife]

That had nuthing to do with what i posted.

 

[bacarl]

Yeah, little confused by that too robin; mis-quote?

Another reason for the lower mileage is that in the winter the engine trys to work harder until normal operating temps are reached. In the summer it doesn't have to do that.

 

[Olestra]

No not misquote, he just didn't explain it fully.

In newer cars, AC comes on with the heater in all modes from "Feet" to everything clockwise.
So, in otherwords, AC comes on with (and those settings in between the following):
Feet
Feet/Defrost
Defrost

Even if you don't have the AC button activated, the AC will automatically run in those situations for the reason stated in an above post (release humidity).

There are multiple other reasons for lower gas mileage, which all add up to give you terrible mileage.

- Tires under inflated
- Longer idling times
- Idle at higher RPMs to warm up engine on initial start up
- Denser air (maybe?)
- Winter tires (more grip = more rolling resistance = friction)
- Winter gas mixture
- More frequent stops due to slower traffic
- Snow creates more resistance to movement

There are probably others I haven't thought of.

 

[bacarl]

perhaps, but what's that got to do with the IMRC sensor -- which is what Infantry's quoted post was about???

btw, are you sure the defroster comes on for the Feet position? I'm inclined to disagree. I don't recall ever hearing the defroster/relay clicking on and off for the Feet position, only those that specify that the defroster will be running.

 

[Olestra]

Oh I see, my bad, Robin did misquote. I think he was trying to reply BluMicar's post.

Anyways, I was pretty sure it was feet and clockwise, I will have to check around to be sure. I think the owner's manual might even have information on this.