How much mpg do you lose in winter?

[SubieRubyRoo]

Hey folks,

How much mpg do you lose in winter vs. the best of what you get in spring/summer/fall?

I don't have a trip computer in my car, but by my manual calculations I got 28 mpg in late summer/early fall and now that temps have plunged here in central Alberta, I only got 23.7 mpg on my last tank. That's a drop of about 15%.

Just wondering if this is normal/typical.

Simple existing math can get you close; for each 10*F reduction in air temp, N/A engines make about 1% more power, and forced induction about 2%. Take this number and multiply it by the rated HP of your engine. Convert that HP # to BTUs, and divide by the average BTU of winter gasoline (I believe kschachn has posted the number before). Then, calculate in divisions of 10, the temperature difference from 70*F. So, if a week’s temp was 20*F, the multiplier would be 5. Multiply that by the number you got when dividing BTUs, and that should give you a decent estimate of the overall mpg “hit” from the colder temps.

In my old 175HP Fusion and my 169HP Transit Connect this works out to about .4 mpg per 10*F drop, and has proved pretty close (when there’s been say a week at roughly the same temps). My 3.5 EcoBoost, with the ~500rwhp tune in it loses roughly 1mpg per 15* drop.

So, when we had 20* weather, I see about a 2-2.2mpg drop in the Transit Connect. The truck would drop from low-mid 21s into the high 16s-low 17s depending on remote start usage.

Maybe I didn’t explain it the best, but if you discard minor variables like tire pressure and gas energy content, I think the calculation based on air temp is probably the best guesstimate since those factors are known to be true based on many years of SAE power testing data and other power/fuel calculations. There’s no real way to calculate the overall impact. It is what it is.

 

[Rmay635703]

2001 Dodge Ram 15mpg summer 8mpg winter

 

[tbm5690]

Simple existing math can get you close; for each 10*F reduction in air temp, N/A engines make about 1% more power, and forced induction about 2%. Take this number and multiply it by the rated HP of your engine. Convert that HP # to BTUs, and divide by the average BTU of winter gasoline (I believe kschachn has posted the number before). Then, calculate in divisions of 10, the temperature difference from 70*F. So, if a week’s temp was 20*F, the multiplier would be 5. Multiply that by the number you got when dividing BTUs, and that should give you a decent estimate of the overall mpg “hit” from the colder temps.

In my old 175HP Fusion and my 169HP Transit Connect this works out to about .4 mpg per 10*F drop, and has proved pretty close (when there’s been say a week at roughly the same temps). My 3.5 EcoBoost, with the ~500rwhp tune in it loses roughly 1mpg per 15* drop.

So, when we had 20* weather, I see about a 2-2.2mpg drop in the Transit Connect. The truck would drop from low-mid 21s into the high 16s-low 17s depending on remote start usage.

Maybe I didn’t explain it the best, but if you discard minor variables like tire pressure and gas energy content, I think the calculation based on air temp is probably the best guesstimate since those factors are known to be true based on many years of SAE power testing data and other power/fuel calculations. There’s no real way to calculate the overall impact. It is what it is.

Many forced induction engines are normalized, so they are not producing as much boost in the winter since lower intake temps allow them to hit power targets without as much help from the turbo. Point is, you don't gain power seasonally in turbocharged engines quite like you do for NA.

 

[fdcg27]

All of the above would only be true if one actually used the additional engine output.

 

[SubieRubyRoo]

Many forced induction engines are normalized, so they are not producing as much boost in the winter since lower intake temps allow them to hit power targets without as much help from the turbo. Point is, you don't gain power seasonally in turbocharged engines quite like you do for NA.

That’s not what SAE says, and it’s not what my boost gauge shows. I make ~21.8 ish boost in the summer, and ~22.6 or so in the winter.

 

[barryh]

I commuted summer and winter on a motorcycle for 14 years and recorded every drop of fuel it used. The mpg graph is a recognisable sine wave that consistently swung by a 13% difference between summer and winter. Being air cooled probably made it worse than it would have been with a water cooled engine that at least runs at a consistent temperature once warmed up. An air cooled engine has no means of controlling excessive winter cooling so doesn't get fully warmed up at all in the winter. I confirmed that by oil temperature measurement.

Although I made the same mpg plots for my car the summer/winter pattern is very much more confused probably because it wasn't being used consistently for the same trips. All you can discern is the highest peaks occurred in the summer and the lowest lows in it he winter. The overall mpg pattern is dictated more by journey length than ambient temperature.

 

[eljefino]

My prius drops from 60 to 47 or so. Running cheapo winter tires, they cause a lot of it.

 

[odie]

3 M.P.G. for the ACCENT . Possibly 4 M.P.G. with studded tires of the FIT . Keep tires at 3 > 4 p.s.i. over the recommended tire pressure .

 

[twX]

Looking at my fuel logs, fuel consumption is 24% higher in Dec-Feb vs Jun-Aug. It can get down to -40 degrees here, and fuel efficiency takes a big hit, even using a block heater and not idling the engine too much.

 

[redtrucker610]

I was under the impression that it was because or winter blend gas. Wouldn’t the ecm also make the fuel mixture a little richer to adjust for the colder temps?

 

[twX]

I was under the impression that it was because or winter blend gas. Wouldn’t the ecm also make the fuel mixture a little richer to adjust for the colder temps?

It's mostly from longer engine warm up, denser air increasing aerodynamic losses, and higher rolling resistance from the tires. The fuel mixture will be richer at low coolant temperatures, but mostly in the first minute after the engine is started, so it's not a huge factor.

 

[andrew_j]

20->18 MPG so about 10%

 

[Number_35]

Hey folks, I've tried to compile a list of reasons mpg is less in winter. Let me know if I've forgotten anything or if I've gotten anything wrong.

1. Lower tire pressure (if you've forgotten to add more air as the temperatures drop).

2. Possibly higher rolling resistance of your winter tires (depends on the tires I guess).

3. Denser cold air means more drag.

4. More engine time spent below normal operating temperature.

5. More time spent idling waiting for the car to warm up.

6. Winter blend gas is a bit less energy dense.

7. Slippery surfaces means more wheel spinning.

8. Some transmissions won't get to higher gears (or lock up the torque converter clutch?) until fully warmed up.

9. Cold temperatures harder on charging system/alternator? (Not sure about this one, just guessing.)

10. Longer nights mean you're more likely to be running your lights.

11. Running the rear defroster.

12. Heavier winter steel wheels maybe.

13. More AWD/4WD usage.

On the other hand there's a few things helping to *increase* mpg in winter too:

A. You've got your windows rolled up presumably, so less drag.

B. You don't have the AC on.

Excellent list!

One more consideration - many vehicles run the AC compressor when the HVAC controls are set to defrost. Such vehicles would run the compressor more in winter than summer (here).

 

[BillyHW]

2001 Dodge Ram 15mpg summer 8mpg winter

Ouch.

 

[BillyHW]

I commuted summer and winter on a motorcycle for 14 years and recorded every drop of fuel it used. The mpg graph is a recognisable sine wave that consistently swung by a 13% difference between summer and winter. Being air cooled probably made it worse than it would have been with a water cooled engine that at least runs at a consistent temperature once warmed up. An air cooled engine has no means of controlling excessive winter cooling so doesn't get fully warmed up at all in the winter. I confirmed that by oil temperature measurement.

Although I made the same mpg plots for my car the summer/winter pattern is very much more confused probably because it wasn't being used consistently for the same trips. All you can discern is the highest peaks occurred in the summer and the lowest lows in it he winter. The overall mpg pattern is dictated more by journey length than ambient temperature.

View attachment 191402

Wow, fantastic graph.

 

[skyactiv]

2001 Dodge Ram 15mpg summer 8mpg winter

That is a 46.7% drop in fuel economy.

 

[BillyHW]

Simple existing math can get you close; for each 10*F reduction in air temp, N/A engines make about 1% more power, and forced induction about 2%. Take this number and multiply it by the rated HP of your engine. Convert that HP # to BTUs, and divide by the average BTU of winter gasoline (I believe kschachn has posted the number before). Then, calculate in divisions of 10, the temperature difference from 70*F. So, if a week’s temp was 20*F, the multiplier would be 5. Multiply that by the number you got when dividing BTUs, and that should give you a decent estimate of the overall mpg “hit” from the colder temps.

In my old 175HP Fusion and my 169HP Transit Connect this works out to about .4 mpg per 10*F drop, and has proved pretty close (when there’s been say a week at roughly the same temps). My 3.5 EcoBoost, with the ~500rwhp tune in it loses roughly 1mpg per 15* drop.

So, when we had 20* weather, I see about a 2-2.2mpg drop in the Transit Connect. The truck would drop from low-mid 21s into the high 16s-low 17s depending on remote start usage.

Maybe I didn’t explain it the best, but if you discard minor variables like tire pressure and gas energy content, I think the calculation based on air temp is probably the best guesstimate since those factors are known to be true based on many years of SAE power testing data and other power/fuel calculations. There’s no real way to calculate the overall impact. It is what it is.

I'm trying to follow, but if a naturally aspirated engine produced more power in cold air, wouldn't you just let off the gas slightly to compensate and achieve the same speed? So why would you see a drop in MPG?

 

[BillyHW]

Looking at my fuel logs, fuel consumption is 24% higher in Dec-Feb vs Jun-Aug. It can get down to -40 degrees here, and fuel efficiency takes a big hit, even using a block heater and not idling the engine too much.

I wonder if anybody has done a calculation of the cost of running a block heater vs. the cost of the gas saved by using one. Of course it would depend on the price of electricity and the price of gas currently where you live, and also the ambient temperature, and your specific engine, but it would be really interesting to see.

 

[Rand]

A fully warmed up vehicle probably only loses 5-10%
but with extended warm up and cold fluids its more like 25% except on extended drives.(ie vacation or hundred+ miles.

My subaru takes at least 15miles to get fully warmed up and even then the gear oil and such is still colder than summer.

My Jeep warmed up pretty fast its winter mpg was better than my subaru even with 100hp more and 800lbs..

I wonder if anybody has done a calculation of the cost of running a block heater vs. the cost of the gas saved by using one. Of course it would depend on the price of electricity and the price of gas currently where you live, and also the ambient temperature, and your specific engine, but it would be really interesting to see.

how about a transmission heater, axle heaters etc.. everything has to warm up.. to achieve good fuel economy. The engine is just part.

 

[BillyHW]

I was under the impression that it was because or winter blend gas. Wouldn’t the ecm also make the fuel mixture a little richer to adjust for the colder temps?

Does more fuel energy go into warming up the air than in driving the piston down?