[arjithin]

Temperature vary between 30 degree Celsius in summer to -10 degrees in winter in northeast USA. I bought my CRV 3 years back and observed that every winter the car returns a lower mpg ( ~4-5 mpg or 20% less compared to summer). This is the 4th winter and same story again. The impact on mpg is more during the first 4-5 miles in a cold start, but the overall mpg returned is less even once the engine reaches the operating temperatures.

My observations - It could be engine not producing enough power (lean burning) or higher rolling resistance. I could feel vehicle speed dropping fast as I step out of the accelerator or higher push in accelerator to maintain a given speed in winter compared to summer in the same daily commute routes. The car feels more rigid in winter.

Would like to understand why this happens, and what can be done to reduce the drop in mpg.

[goandude]

Originally Posted by arjithin

Temperature vary between 30 degree Celsius in summer to -10 degrees in winter in northeast USA. I bought my CRV 3 years back and observed that every winter the car returns a lower mpg ( ~4-5 mpg or 20% less compared to summer). This is the 4th winter and same story again. The impact on mpg is more during the first 4-5 miles in a cold start, but the overall mpg returned is less even once the engine reaches the operating temperatures.

My observations - It could be engine not producing enough power (lean burning) or higher rolling resistance. I could feel vehicle speed dropping fast as I step out of the accelerator or higher push in accelerator to maintain a given speed in winter compared to summer in the same daily commute routes. The car feels more rigid in winter.

Would like to understand why this happens, and what can be done to reduce the drop in mpg.

Surprising, as engines should run better with the higher density of air. But OTOH this increase in density would increase wind resistance. Another thread on the better winter running is here http://www.team-bhp.com/forum/techni...ng-better.html

[GTO]

In the typical Indian winter, cars actually feel & perform much better (Link to thread). However, that's because our summers are so very severe.

East coast winters can freeze you to the bones (been there, done that). I think you'll be seeing a lower MPG because:

- Engine takes a lot more time to reach optimal temperatures. And right after start, the engine idles at a high rpm for too long a time.

- Even if I had to wait for 5 minutes, I'd keep the car running (just to keep the interiors warm). That's not the case in pleasant weather where you'd switch the engine off.

- Slower average speed, as a result of cautious driving in the adverse conditions.

- Lower tyre pressures. Unless you increase the PSI by 1 - 2 points.

- I frequently drive in a lower gear when driving in slippery conditions, and I'm sure you do too.

- Increased load on the car : From the heater, wipers and lights

[noopster]

I like our Indian definition of winter much better than the classical one! Don't think I could survive one of 'em Northeastern winters...

Over here, winters are better for FE. Case in point.

[tsk1979]

Do you use heating?
Many western cars use electrical heaters(instead of using radiator heat) which run off engine power. Using heating in such cars will lower your mileage.

[volkman10]

Added to the above points,cold temperatures lower the pressure in the tyres. When the weather turns bad( snow,etc), vehicles must work harder to push through snow and slush. Both of these conditions equal greater rolling resistance and more fuel used to cover the same distance!

Cheers!

[bblost]

Could the additives added to fuel for use in freezing temperatures have anything to do with lower mpg?

[vina]

Originally Posted by bblost

Could the additives added to fuel for use in freezing temperatures have anything to do with lower mpg?

Actually it isn't just additives, the composition of fuel itself changes. Gasoline is a mixture and the refineries (US based) change it to keep it from becoming too viscous in winters.

In addition, as GTO wrote, there are several practical factors - heating usage is more (whether you have electrical heater or direct heating from engine - ultimately that burns fuel), driving conditions are less friendly etc.

By the way, colder air is denser and hence will help engine generate more peak power than it otherwise could (with warmer air) - as far as FE in similar driving condition goes, the denser air is not very useful, and engine does need to keep warm - more fuel will actually be used up to keep engine warm and to keep lubricants flowing.

[Mpower]

If you are in snow or slippery conditions, there is constant wheel spin that results on loss of energy and hence low FE.

But the big killer is cold starts and short drives.

[Aroy]

. Cold start
. Lower tyre pressure
. Heater
. Tyre slippage

All of these contribute to lower FE.

[arjithin]

Thanks for all your inputs.

Originally Posted by vina

as far as FE in similar driving condition goes, the denser air is not very useful, and engine does need to keep warm - more fuel will actually be used up to keep engine warm and to keep lubricants flowing.

- Does this make a big impact?

Consider this scenario - A non stop 100 mile drive in an interstate highway from my home to my sisters home which I do atleast once every month.
In summer, I normally get 30 mpg, I use a/c in the lowest speed.
In winter, outside temp is 1 degrees, no snow, no ice, tire pressure is 31-32 psi (same all season Michelin tires) which is 1-2 psi higher than normal, I use heater for the first 5 minutes or so, once the car is in highway, the radiator heat is enough to keep us warm.
I drive the same way as summer, but i get 25-25.5 mpg max for this trip. As mentioned in the original post, I can literally feel engine working hard to keep the speed and vehicle loosing speed fast once compared to summer. The vehicle doesnt feel smooth ( compared to winter) as well.

With the above points, I can correlate only the denser air as the probable reason in the above scenario. What else you can think of?

I raised this with my Honda service station, but they too cant give a satisfactory answer. I didnt see this pattern with my older car, but the pattern repeated 4 times with my CRV.

Note: I squeezed 35 mpg from my CRV once in a summer round trip in the same stretch (tankful to tankful)

[infotech58]

that looks like perfectly normal. i have stayed in Indiana for many years and have observed a fuel mileage drop on most of my cars during winters. an Accord V6 used to give me 22-23 MPG in city in summers and in winters the same delivered 16 MPG. there are various factors (in addition to the ones already mentioned by GTO) which i read about when i was looking for the same answers few years ago:

1 - vaporization of gasoline is not very efficient at cold temperatures (related with the additives to fuel). there is much more to this concept which i do not remember on top of my head; google it.

2 - in colder temperatures engine oil/transmission oil/other fluids are thicker and hence more power is required to overcome the reduced lubrication or increased drag.


the Nissan Xterra I owned was an exception to this and it delivered 16 MPG in ALL conditions (highway driving or city driving or summer or winter or sedate driving or spirited driving; it was like a tractor which consumes fuel on hourly basis).

[vasoo]

In addition to the factors listed above, I think it will be a good idea to check the condition and grade of the engine oil and make sure that it is suitable for the weather where you drive. Quicker drop of speed somehow makes me feel that there is higher levels of friction (too viscous oil?) or possibly lower fuel combustion happening (do an emission test).

See the link below for some explanation

http://www.artsautomotive.com/public...-mileage-story

[Aroy]

While pinpointing engine oil, we forget the other contributors to friction in cold weather
- Gear box oil
- Differential oil
- Wheel bearing grease
also
- Cold batteries, loose charge faster and require more current for charging
- Alternator may be working harder initially when its bearing lubrication is cold
- If it is snowing wipers will be working harder

[noopster]

I really think arijith is making too big a deal over this. 30 mpg, which he claims to regularly get, is equivalent to 12.75 kmpl. And 25 mpg is 10.625 kmpl. Both these are pretty good numbers for the petrol CRV - friends in India say they get 6-7 kmpl regularly. Admittedly, the conditions are not the same, but that much variance is something to be expected even in normal running (city vs highway,or summer vs winter) so why are you so worried?