interesting gas milage notice.

[rocking23nf]

so all winter, I do basically the same route, 2-3 KM with 3-4 red lights, then 20KM of highway driving at 110km/per hour, then another 8km of city driving with up to 20 lights.

My fuel estimator has been pretty much locked in at 10.1 to 10.2L/100KM, I live in Alberta, tempuratures are usually in the minus 10C range in the mornings during the commute and maybe up to -5 in the evening commute.

the last 2 weeks have been warm, around freezing during the morning commute, and 5C in the evening commute.

My L/100K has dropped down to 9.9, and I went from estimating 570KM to a tank, to around 650KM to a tank.

not complaining of course, just didn't think that slight change in weather would make such a difference. my hunch is that the car drinks more gas during the engine warmup phase, which is shorter depending on the weather?

Anyone else see this?

 

[vroom]

Normal. The Skyactive engine spends a lot of gas warming up when its cold. I go from around 10.4 L/100KM in winter to about 8.0 L/100KM in summer. So good news, it'll just get better!

 

[yugrus]

I do here in Ontario. Our temperatures are not as bad though, however, we hit -20C-something the other week.
The ECU has to maintain stoichiometric air/gas ratio in closed loop mode. Air mass increases for the given volume when temperature drops. Air becomes more dense. So the computer has to inject more gas in every compression stroke to maintain the stoichiometric ratio. That, on top of the longer open-loop warm-up period gives you lower mileage.

 

[rocking23nf]

I have found that most mornings the Blue engine light has not gone off until I hit the highway phase of my drive.

 

[Goguinness]

Isn't winter gas also formulated different, and less efficient?

 

[yugrus]

Isn't winter gas also formulated different, and less efficient?

Yep, that too, big time.

 

[vroom]

Air gas ratios and winter mixes probably have something to do with it, but from experience very little compared to warm up. I can easily go well below 8 L/100km on long highway trips (say 3 hours) at - 20C with winter gas in my tank, just because the warm up time becomes small compared with the total trip.

As far as stoichiometric ratios, cold air is more dense and has even more oxygen in proportion because of a far lower water content, so yes, it amounts to more gas being needed for the same air volume, but it should also translate to more bang for the buck, so in the end it should not make a large difference. In fact, cold, denser air probably has a larger impact aerodynamically.

 

[yugrus]

As far as stoichiometric ratios, cold air is more dense and has even more oxygen in proportion because of a far lower water content, so yes, it amounts to more gas being needed for the same air volume, but it should also translate to more bang for the buck, so in the end it should not make a large difference. In fact, cold, denser air probably has a larger impact aerodynamically.

I used to think this way too. But if you don't need that extra power, or pep, you're still burning more gas, mandated by the ECU settings, even cruising at 50mph. More oxyfen, more fuel burned. Although yes, there is a benefit to power junkies, you squeeze relatively more power out what you've got, when it's cold...

 

[vroom]

Not sure because that would also mean that you have to depress the gas pedal just a bit less to maintain you speed.

In any case, even if you were right in theory, as I said I manage very similar MPGs on long trips in both winter and summer. Real life experience make any theoretical consideration kind on moot (even if they are interesting to discuss!)

 

[Unobtanium]

This is part of why I average around 22-23mpg. Short trips to work. Almost always in warm-up cycle.

 

[yugrus]

My wife gets consistent 23mpg commuting to work in winter on her 5mi trip. We normally take the car on a long drive (200+ mi) at least once a week, to burn off the fuel/water dilution and to keep the exhaust rust in check. This helps bringing the fuel consumltion down.
By the way, I noticed that the exhaust gets way more rust then normal in our climate, despite being stainless steel. Has anyone noticed that ad well?

 

[GAXIBM]

I do here in Ontario. Our temperatures are not as bad though, however, we hit -20C-something the other week.
The ECU has to maintain stoichiometric air/gas ratio in closed loop mode. Air mass increases for the given volume when temperature drops. Air becomes more dense. So the computer has to inject more gas in every compression stroke to maintain the stoichiometric ratio. That, on top of the longer open-loop warm-up period gives you lower mileage.

The throttle and the length of time the intake valves remain open in the Miller Cycle reduce the amount of air entering the compression stroke to what you need for the power requested. I think heating the cat quick to reduce emissions kills very cold startups and the dense air/stiff rubber tires and winter gas don't help...

 

[MikeM.]

I used to think this way too. But if you don't need that extra power, or pep, you're still burning more gas, mandated by the ECU settings, even cruising at 50mph. More oxyfen, more fuel burned.

The colder air has more oxygen but that will not cause more fuel to be injected at the same rpm/vehicle speed because the variable valve timing will automatically adjust to let less air in due to the fact that it is more dense.

 

[yugrus]

The throttle and the length of time the intake valves remain open in the Miller Cycle reduce the amount of air entering the compression stroke to what you need for the power requested.

I thought Miller Cycle was all about elongation of the intake valve open position timing, way past the beginning of the compression stroke, to increase volumetric efficiency. Not reducing the open valve timing.
Electronic control of the throttle means it is as much wide open as it could be, providing the inputs, to reduce air restrictionn.
Only happens in fully warmed-up engine, within closed loop. If the loop is closed, it is stoichiometric ratio, no deviations. I'd like to see the data to the contrary, would be glad to stand corrected.

 

[banjos-n-beer]

Isn't winter gas also formulated different, and less efficient?

Yes, and couple that with Ethanol (we have 10% Ethanol gas, or so the pump states) and colder weather and you're probably bound to get lower MPG than advertised.

However, I decided to finally take a fuel measurement since I've only been relying on the computer to tell me my MPG. The trip was 284 miles round trip, with probably 270 miles of it Highway, and 14 secondary and backroad miles at speeds between 30 and 40 MPH. I did my best to maintain a steady 75 MPH on the highway, but did have to pull up to 80 a few times to keep up with the pace of Boston traffic. Wind was light, and temps were around 40F on average, but were in the 20sF when we departed.

The results? 284 miles traveled, 10.256 gallons used. That equates to 27.7 MPG on winter blend with Ethanol. I also have studded snowtires on at the moment.

I'm eager to test again with my summer tires and gas blend. So far I am very happy with my CX5's MPG, and struggle to understand why a certain number of folks get such worse stated results.

 

[MikeM.]

I'm eager to test again with my summer tires and gas blend. So far I am very happy with my CX5's MPG, and struggle to understand why a certain number of folks get such worse stated results.

Most people who get low mpg numbers admit to one or more of the following:


1) considerable "warm-up" idling
2) regular highway speeds of 80 mph
3) Traffic congestion, stop/go.
4) Many short trips with a cold engine

 

[GAXIBM]

I thought Miller Cycle was all about elongation of the intake valve open position timing, way past the beginning of the compression stroke, to increase volumetric efficiency. Not reducing the open valve timing.
Electronic control of the throttle means it is as much wide open as it could be, providing the inputs, to reduce air restrictionn.
Only happens in fully warmed-up engine, within closed loop. If the loop is closed, it is stoichiometric ratio, no deviations. I'd like to see the data to the contrary, would be glad to stand corrected.

We are saying the same thing - my quote "intake valves remain open" - your quhote "elongation of the intake valve open position timing".
When not in Miller Cycle, the throttle limits the air to what is needed for the power requested. No extra fuel needed to meet fuel air targets in either case...

 

[Unobtanium]

Most people who get low mpg numbers admit to one or more of the following:


1) considerable "warm-up" idling
2) regular highway speeds of 80 mph
3) Traffic congestion, stop/go.
4) Many short trips with a cold engine

But I've never seen these things cause bad mileage in relation to epa ratings before. I treat all my vehicles the same. The cx5 reacts very poorly to this treatment while the others kept returning their epa ratings or close to. For example, my jeep got 14.5mpg in normal daily use. My cx5 gets 22.5 to 23.5. 70% highway, 30% non congested (mostly) city

 

[MikeM.]

We already know you had a magic Jeep. Too bad it constantly needed expensive repairs.

 

[Chris_Top_Her]

I thought Miller Cycle was all about elongation of the intake valve open position timing, way past the beginning of the compression stroke, to increase volumetric efficiency. Not reducing the open valve timing.
Electronic control of the throttle means it is as much wide open as it could be, providing the inputs, to reduce air restrictionn.
Only happens in fully warmed-up engine, within closed loop. If the loop is closed, it is stoichiometric ratio, no deviations. I'd like to see the data to the contrary, would be glad to stand corrected.

I can check with torque pro to see what the afr is during initial start up