So it begins. Cooler air = Worse MPG - Honda CRZ Forum: Honda CR-Z Hybrid Car Forums
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post #1 of 24 (permalink) Old 09-09-2016, 01:40 PM Thread Starter
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So it begins. Cooler air = Worse MPG

heading into the fall and winter temps, my MPG has already dropped, thanks to my morning commute. All summer, it was >75F in the morning. the last week, it has been <70F, and I"ve dropped from 43mpg highway average down to 40mpg highway average.

Back in March, I was getting around 38, when outside temp was around 45F

Going to take the snorkel off the intake box for a free hot-air intake this weekend and see what the warmer intake air gets me.
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post #2 of 24 (permalink) Old 09-09-2016, 01:54 PM
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Originally Posted by 96firephoenix View Post
heading into the fall and winter temps, my MPG has already dropped, thanks to my morning commute. All summer, it was >75F in the morning. the last week, it has been <70F, and I"ve dropped from 43mpg highway average down to 40mpg highway average.

Back in March, I was getting around 38, when outside temp was around 45F

Going to take the snorkel off the intake box for a free hot-air intake this weekend and see what the warmer intake air gets me.
This is interesting as I have found my MPG on my previous car when it got cooler it went up not down. I have to check my log book for The Speed Bump. I have found my mileage on The Speed Bump has changed quite a bit since I started playing with the modes and change in location. I still find the MPG on The Speed Bump beats my previous car by quite a bit and I am happy to feed it as much fuel as it wants!

Is it possible the drop in air pressure in the tires is part of your cause?
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post #3 of 24 (permalink) Old 09-09-2016, 02:47 PM Thread Starter
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This is interesting as I have found my MPG on my previous car when it got cooler it went up not down. I have to check my log book for The Speed Bump. I have found my mileage on The Speed Bump has changed quite a bit since I started playing with the modes and change in location. I still find the MPG on The Speed Bump beats my previous car by quite a bit and I am happy to feed it as much fuel as it wants!

Is it possible the drop in air pressure in the tires is part of your cause?
well, what causes the drop in tire pressure?

I'll check them too, but I've been intending to pull the snorkel anyway, since more constant intake temp = more constant MPG year-round in theory.

All of my other cars have gotten worse mpg in winter (exception being my Explorer. That gets 17mpg...in all conditions). I've been able to offset that on a couple cars by using premium or mid-grade, but that is only cost-effective on the CR-Z when the higher grade is less than 30 cents more per gallon (assuming that it boosts my mpg back up to 42, which it probably won't).
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post #4 of 24 (permalink) Old 09-09-2016, 03:10 PM
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well, what causes the drop in tire pressure?

I'll check them too, but I've been intending to pull the snorkel anyway, since more constant intake temp = more constant MPG year-round in theory.

All of my other cars have gotten worse mpg in winter (exception being my Explorer. That gets 17mpg...in all conditions). I've been able to offset that on a couple cars by using premium or mid-grade, but that is only cost-effective on the CR-Z when the higher grade is less than 30 cents more per gallon (assuming that it boosts my mpg back up to 42, which it probably won't).
Drop in air temperature causes drop in tire pressure. I check my tire pressure every 2 weeks. I take it you never check yours or have had nitrogen put in your tires? But you may just be joking with me.

Cold Air being denser should give you better Fuel economy in theory. This is what is behind the whole concept of forced induction. The CR-Z may have something in it's tuning that is over compensating for the temperature change though.
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post #5 of 24 (permalink) Old 09-09-2016, 03:57 PM

 
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I have almost exclusively gotten better fuel economy in winter, but you could argue that Arizona doesn't "get" winter and that an average low of 40 is small time. I absolutely love running the heat with the windows down, getting auto stop at every light. But, I don't have the defroster and insane humidity ruining that.



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post #6 of 24 (permalink) Old 09-09-2016, 04:18 PM Thread Starter
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But you may just be joking with me.
The winky face was the hint that I was joking.
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Cold Air being denser should give you better Fuel economy in theory. This is what is behind the whole concept of forced induction. The CR-Z may have something in it's tuning that is over compensating for the temperature change though.
In theory... like I said, I've never gotten better mpg in winter in any vehicle. I think that can mostly be attributed to winter fuel additives depressing the effective octane rating... I get that the octane rating isn't a measure of how much power you get from the gas, but with EFI engines that have octane sensors, they typically alter the timing slightly to get optimal power out of the gas without causing any knock... so the engine is retarding the timing on what it senses as lower octane gas, which puts the explosion at a less-than-best point in the stroke.

Just my theory.
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post #7 of 24 (permalink) Old 09-09-2016, 04:53 PM
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The winky face was the hint that I was joking.

In theory... like I said, I've never gotten better mpg in winter in any vehicle. I think that can mostly be attributed to winter fuel additives depressing the effective octane rating... I get that the octane rating isn't a measure of how much power you get from the gas, but with EFI engines that have octane sensors, they typically alter the timing slightly to get optimal power out of the gas without causing any knock... so the engine is retarding the timing on what it senses as lower octane gas, which puts the explosion at a less-than-best point in the stroke.

Just my theory.
Try experiments with Octane boosters but I just drive and if I take the hit I take the hit.

It may be the more rolling resistance from the winter tires too.
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post #8 of 24 (permalink) Old 09-09-2016, 05:02 PM Thread Starter
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Try experiments with Octane boosters but I just drive and if I take the hit I take the hit.

It may be the more rolling resistance from the winter tires too.
haven't gotten the winter tires yet. I'm still on the (factory?) all-seasons it had when I got it.

I'm not really wanting to get the octane boosters... math says they aren't money ahead on just buying higher octane gas.
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post #9 of 24 (permalink) Old 09-09-2016, 05:19 PM
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haven't gotten the winter tires yet. I'm still on the (factory?) all-seasons it had when I got it.

I'm not really wanting to get the octane boosters... math says they aren't money ahead on just buying higher octane gas.
If you only need a little bit more then the boosters make sense. If you need a lot more than the higher octane fuel makes more sense. All in all I just take the hit in either direction on temp versus MPG. The CR-Z is so much better on fuel than my Grand Prix GTP which required Minimum 91 octane fuel.

The much smaller tank on the CR-Z makes adding boosters less expensive usually the bottles are for 25 gallon tanks.

But you are right it may just be the winter blend fuels.
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post #10 of 24 (permalink) Old 09-09-2016, 07:00 PM
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Tire pressure drops even without a change in temperature due to permeation, about 1psi a month but you also lose about 1psi for every 10F drop in temp at passenger car pressures. So if you haven't checked your pressures in two months and the temps have dropped 30F then you could be down by 5psi or more. Some tires permeate more than others. Winter Tech Information - Air Pressure, Temperature Fluctuations

Its more than just winter fuel blends. Running higher octane has been beaten to death as a waste of money on vehicles that don't specifically require it (forced induction/highly modified members disregard).

"Cold weather affects your vehicle in more ways than you might expect:

Engine and transmission friction increases in cold temperatures due to cold engine oil and other drive-line fluids.
It takes longer for your engine to reach its most fuel-efficient temperature. This affects shorter trips more, since your car spends more of your trip at less-than-optimal temperatures.

Heated seats, window defrosters, and heater fans use additional power.

Warming up your vehicle before you start your trip lowers your fuel economy—idling gets 0 miles per gallon.

Colder air is denser, increasing aerodynamic drag on your vehicle, especially at highway speeds.

Tire pressure decreases in colder temperatures, increasing rolling resistance.

Winter grades of gasoline can have slightly less energy per gallon than summer blends.

Battery performance decreases in cold weather, making it harder for your alternator to keep your battery charged. This also affects the performance of the regenerative braking system on hybrids."
https://www.fueleconomy.gov/feg/coldweather.shtml
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