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Discussion Starter #1 (Edited)
My last tank was from an off-brand (Valero) and only got me 65mpg (I know, great, but not based on my recent tanks). When I filled up, I was told it was winter gas and I never used the cabin heat. Based on my previous tanks, that tank took about a 10% hit in mpg. Yesterday, I filled up at my normal gas place (local Speedway) and was also advised they were on winter gas. My r/t to work was nearly my norm I got all summer (71mpg). I used passive heat with temps in the lower 50s. Perhaps cabin heat is a bigger influence on mpg than winter fuel?

Let's use this thread to track how winter fuel affects our MPGs. Our goal should be to find the biggest influencer on efficiency. Some of us already have had a full winter to deal with. I've seen cabin heat be a major culprit (unless you wear mittens and don't use it). Let's help each other make the most of our Insights. C'mon! We can't let Toyota or Hyundai beat us! Go Insights! #mpgocd #brandsmatter
 

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Adding some observations posted last year in the Winter MPG thread, to help build the 'database':
- 20% decrease from winter gas (before snow tires) noted by @Thack (with additional results posted on Fuelly) in Canada
- 25.6% decrease from winter gas plus snow tires noted by @Misterb in Canada
- 18% decrease in winter noted by @BabyBleu in Pittsburgh
- 15% decrease in winter noted by @ronnie on cross-country drive
- 29% decrease in winter noted by Fuelly member
- 18 to 21% decrease with winter tires and winter gas noted by @Insight'nAround
- 15% decrease in winter noted by @hobokencentral

Temperature-related observations:
- 16% decrease in cold weather (near 0) versus warmer winter weather (40-50) noted by @FRR
- 10% decrease in 30F versus >50F winter weather noted by @gerryzub
- 18% average decrease in 30F versus >50F weather noted by @dr_glenn
 

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My last tank was from an off-brand (Valero) and only got me 65mpg (I know, great, but not based on my recent tanks). When I filled up, I was told it was winter gas and I never used the cabin heat. Based on my previous tanks, that tank took about a 10% hit in mpg. Yesterday, I filled up at my normal gas place (local Speedway) and was also advised they were on winter gas. My r/t to work was nearly my norm I got all summer (71mpg). I used passive heat with temps in the lower 50s. Perhaps cabin heat is a bigger influence on mpg than winter fuel?

Let's use this thread to track how winter fuel affects our MPGs. Our goal should be to find the biggest influencer on efficiency. Some of us already have had a full winter to deal with. I've seen cabin heat be a major culprit (unless you wear mittens and don't use it). Let's help each other make the most of our Insights. C'mon! We can't let Toyota or Hyundai beat us! Go Insights! #mpgocd #brandsmatter
Well I'm on winter gas. Its cooler too. We have days of wet roads, where overcast from frequent showers discourages drying out of the pavement, which in turn leads to the mpg hurting "drag" of increased tire roll resistance.

Mpg on short trips is especially hurt due to more engine warm up cycles, Occuring with each power off at end of short trip. Using my landmark process I'm finding short trips that yielded 45 mpg are now 25 mpg, sometimes less. Temperatures vary from mid 50's to low 60's.
Am making good use of the warm up cycles to run the heater (using manual not automatic climate control settings), while the engine is on, so must now remember to turn it off, in order access EV mode. Though I keep my light jacket on, the cabin temperature is quite comfortable.

Daily mpg which routinely hit the mid 70's mpg by late Aug. and into Sept., have slipped to the low 70's, and just 69.5 yesterday. But am enjoying "a blast from the past" with some Metallica and Ozzie's Boneyard on XM radio! :)
 

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2019 Honda Insight EX (White Orchid Pearl)
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I took a 3-4mpg hit with current temps between 50F-65F along with winter gas(no heater usage yet).

Long trips: 60-65mpg
Short trips: 48-53mpg

I'm currently doing enough long trips to cushion the lower mpg I'm getting on the short trips. I did a 55 mile trip yesterday and got 62.1mpg. Had ACC set at 65mph with short bursts of 70mph-80mph.
 

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Since my commute doesn't change much, I thought I'd add that currently I'm seeing about a 4mpg loss in average. But I haven't checked tire pressure yet for October, I suspect that I'll be adding some air.

We are in winter gas, and I can attest that cabin heat plays a large role in fuel economy. I try my best to use it as little as possible when needed (mainly for defrosting). What I've been working on, is using it in a burst style method.

I start my drive as normal as possible (unless I can't see, then I use a similar modified method):

So no cabin heat/defrost etc. I let the ICE kick in, and as soon as it stops during my drive I know it's at operating temperature. Unless I'm stopped at a light, I turn on the heat or defrost at 72*, as soon as I feel warmth, I crank the blower speed to max and let it run for 30 seconds. I then turn it off and enjoy passive heat method.

If I need it to clear my windshield to drive. I start the car, put it in sport mode, let it run for one minute. Then turn on defrost at 72*, as soon as the window is cleared, I turn off climate control and put the car in eco and enjoy passive heat.

I find that if I can weather *no pun intended* the weather without any climate control, I can actually beat my summer time numbers with AC. It's all good until the fiancé gets in the car, she's always cold, and always wants the heat on.
 

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My mileage dropped from 59-60 to 55-56 just due to cooler temperatures. I haven't had to fill my car since I put summer gas in it a few weeks ago. (I don't drive if I don't have to. . . it's nice being
retired). . .
 

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My mileage dropped from 59-60 to 55-56 just due to cooler temperatures. I haven't had to fill my car since I put summer gas in it a few weeks ago. (I don't drive if I don't have to. . . it's nice being
retired). . .
I saw similar mpg effect with a 15-20F drop in temp (from 60+F to 40-50's F) and while still on summer gas. Was this similar to your 'cooler' temperature range? If not, over what temperature difference did you see your reported mpg results?
 

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I started trying to find the exact difference between winter blend fuels and summer blend (there are over 20 different blends in the USA at any given time).

Biggest things I've been able to confirm, winter blend has a lower evaporating point (generally represented in the form of RVP (Reid Vapor Pressure) rating.) Most winter blend fuels use simpler and lighter additives such as butane which is more volatile (affects RVP), but has less energy content than Octane. The additives in winter mix are generally cheaper, and require little maintenance to switch over from summer blend. This combined with less driving during winter months is why winter gas is cheaper.

Summer Blend gasoline generally contains heavier additives, to help reduce volatility. The major purpose of this is so that the gasoline doesn't evaporate before reaching the cylinder, preventing vapor lock, and reducing emissions. The additives for summer blend are harder to implement in the refinery process, so the gas companies tend to do their yearly maintenance at the same time as the fuel switch. The downtime, and more expensive additives are why every spring we see a spike in fuel prices.

The EPA estimates the energy content of Summer fuel is 1.7% greater than winter fuel, which has a small impact on fuel economy.

How Stuff Works, Fuel Blends
 

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Anybody know how to improve winter gas? Maybe an octane booster?i want to take advantage of the colder temps and no AC use to maximize mpg..

Also kind of off-topic , but does anyone use Lucas, Chevron, etc fuel system cleaners? I have a bunch of big Lucas bottles I got for free so I’m going to start using it.
 

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I wouldn't think an octane booster would help, especially if you deal with cold temperatures. Octane rating = resistance to detonation. Higher octane fuel is actually harder to burn than lower octane fuel. If you check out the thread, winter-gas-effect-mpg you'll find tips on how to maximize fuel economy in the winter.

Check air pressure in tires.
Don't idle, don't "pre-warm" car.
Try to minimize use of cabin heat.
Try to take less longer trips, than frequent short trips.

Just to name a few.
 

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Does the energy content really matter though? If I understand the power train correctly, the ICE is primarily spinning the generator at a fairly fixed rate, with battery assist as needed, and the ICE only directly engages when speed dictates (the most efficient portions of the ICE power band), and even then it’s concurrent with the electric drive. With this and the ICE typically operating at a fairly constant RPM and load, does fuel energy content actually matter?
 

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Does the energy content really matter though? If I understand the power train correctly, the ICE is primarily spinning the generator at a fairly fixed rate, with battery assist as needed, and the ICE only directly engages when speed dictates (the most efficient portions of the ICE power band), and even then it’s concurrent with the electric drive. With this and the ICE typically operating at a fairly constant RPM and load, does fuel energy content actually matter?
Minimally, less than in a traditional ICE car, except at prolonged periods of highway speeds.

As a hybrid we have other cold related efficiency losses that will affect our cars more. Primarily battery charging/discharging, cabin heat use, and road conditions, as our cars are built for efficiency (minimized Coefficient of drag, and rolling resistance), any additional rolling resistance and drag hurts. I'd suspect that rolling resistance is a greater factor than drag alone, unless the vehicle is used primarily at highway speeds.
 

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Does the energy content really matter though? If I understand the power train correctly, the ICE is primarily spinning the generator at a fairly fixed rate, with battery assist as needed, and the ICE only directly engages when speed dictates (the most efficient portions of the ICE power band), and even then it’s concurrent with the electric drive. With this and the ICE typically operating at a fairly constant RPM and load, does fuel energy content actually matter?
I think it does matter, but at an amount that is likely roughly equal to the degree that fuel energy content differences influence the mpg of a non-hybrid car.

However if load is held constant, than a higher energy fuel will likely need lower RPM, than the same load using a lower energy fuel in the same ICE / generator system.
 

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As an update, I'm seeing a -18% impact on fuel efficiency, which is similar to the results recapped in post #2 from last winter. But more specifically, I think -13% impact is from winter gas, and -5% impact is from lower temperatures.

Observations from standard daily drive route with passive heating as constants:
- Summer gas at 50*F = 60 mpg (baseline)

- Summer gas at 35*F = 57 mpg (-5% impact from temperature change alone)
- Winter gas at 35*F = 49 mpg (-18% impact from temperature and gas change)​


Summer blend is 'only' stated to have +2% more energy value over winter gas, but drive observation suggests a bigger (13%) net effect on cold weather fuel efficiency.
 

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Discussion Starter #15
As @insightfully pointed out via a graphed comparison of my MPG vs. ambient temperature over time, weather (temperature in particular) is a HUGE factor.

My drive in today was with winter fuel, but the temps were in the low-50s. I got 72.3mpg for the 50-mile drive to work. This rivals what I was getting in the summertime.
 

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Adding 'the chart' posted in break-in thread for quick reference here. Top graph is temperature (hi, lo) and middle graph is mpg.

The temperature and mpg curves have such a similar pattern (excluding noted exceptions/reasons) that one might say being able to predict the weather would help to predict fuel efficiency (weather forecast = mpg forecast) -?

 

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My ratings for cooler temps went from being in the 70's/80's down to the 40's. Temps in Denver have been variable--down to 3 degrees one night and up to the 70's again
in just a few days. Crazy weather, not the usual consistent fall temps.
 

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Our INSIGHT is horrible mpg (per average) when I turn the HEATER ON. This car is meant for no heater, and speeds less then 60mph

Temp: 30 F and Below

@75mph

Fuel economy Avg. 32mpg-38mpg

😞😞😞😞
 

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Our INSIGHT is horrible mpg (per average) when I turn the HEATER ON. This car is meant for no heater, and speeds less then 60mph
Agree... but would add that this applies to all hybrids, by the nature of how they're designed to run/function. It's different by design from a traditional car, so otherwise not an apples-to-apples comparison.
 

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The hardest truth is the simplest:

ICE cars will always be the most consistent in the gas mileage department, they are designed to be at 100% run time (at least while driving).

Hybrid cars are extremely susceptible to environmental factors, drive style, creature comfort tax etc... Hybrid efficiency is directly related to how many miles we can cover with the ICE off/ vs miles with ICE running. Those that are getting better gas mileage, are mitigating these factors to their best advantage, giving up certain factors. Those with the least winter impact will always have long sub-70mph commutes, or a heated, or at least relatively warm garage.

Quick update now that I've got 1000+ miles into this winter season, averaging 46.2mpg vs 52.7 (11,000 mi) summer average. I'll be honest, I go pretty extreme on mitigating what I can. Generally my car is driving with absolutely no active climate control, and I'm in my hat, winter coat and gloves. (Approximately 90-93% of my winter drive time this season).
 
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