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MPG decrease in very cold weather??

Posted By: 2009Caraman

MPG decrease in very cold weather?? - 01/11/20 04:34 AM

I'm kinda new to driving and was wondering what kind of penalty I can expect in extremely cold weather(-20c sustained)? Drives are typically 15mins or less.

I replaced my lower intake manifold gasket and though performance has returned fuel economy has slightly dropped. It's only been a 1/2 tank though and since i did the repair it's been at least -15c every day. I'd like to hear your thoughts or observations on mileage in the cold.
Posted By: Rmay635703

Re: MPG decrease in very cold weather?? - 01/11/20 04:37 AM

It can drop in half

Depends on how cold and how short your trip
Posted By: JohnnyJohnson

Re: MPG decrease in very cold weather?? - 01/11/20 04:39 AM

Well how long is it going to take for that engine to warm up and that engine idle to drop below 1800 RPM?
Posted By: 2009Caraman

Re: MPG decrease in very cold weather?? - 01/11/20 04:45 AM

Originally Posted by JohnnyJohnson
Well how long is it going to take for that engine to warm up and that engine idle to drop below 1800 RPM?


It idles at 800rpm at startup then falls to 700 in about 5 mins and gets to temp by the time I get to work 15mins.
Posted By: RDY4WAR

Re: MPG decrease in very cold weather?? - 01/11/20 05:31 AM

Cold air is more dense also. That means more wind resistance when driving through it. Slight, but it's there.
Posted By: Rolla07

Re: MPG decrease in very cold weather?? - 01/11/20 05:35 AM

How much are you idling? I can ssy my mpg went from 17-18 to 14-15 in winter. All short trips. Granted I am am idling alot more whereas i dont ever idle in spring, summer, or fall...
Posted By: GMBoy

Re: MPG decrease in very cold weather?? - 01/11/20 05:55 AM

The winter blend fuel costs a little MPG's as well.
Posted By: edyvw

Re: MPG decrease in very cold weather?? - 01/11/20 06:34 AM

Originally Posted by 2009Caraman
I'm kinda new to driving and was wondering what kind of penalty I can expect in extremely cold weather(-20c sustained)? Drives are typically 15mins or less.

I replaced my lower intake manifold gasket and though performance has returned fuel economy has slightly dropped. It's only been a 1/2 tank though and since i did the repair it's been at least -15c every day. I'd like to hear your thoughts or observations on mileage in the cold.

What car? What oil is in the car? Is it in garage?
Whatever you do, first few km's do not turn on heat and vent for 2-3km's as that delays warming up. Also, do not idle longer than necessary to put seatbelt, get accomodated. Move and move slowly, allowing transmission (assuming it is automatic) to [censored] around 2,000rpms.
Posted By: pitzel

Re: MPG decrease in very cold weather?? - 01/11/20 07:02 AM

At -35C, right after startup, on a car that typically gets 32mpg, the real-time MPG (on flat land) can be as low as 4-5mpg on my car. Early 1990s 3.1L GM V6.

Yes, it improves rapidly as things warm up, but on a 15 minute drive, you'll be exposed to a lot of such operation unfortunately.

Transmission keeps it in first gear for quite a while. To get it into second when its that cold feels like total abuse the revs required. The transmission doesn't have electronics (all vacuum or oil driven), so just the sheer viscosity of the fluid causes that behavior.

BTW, welcome to the forums! Glad to see another fellow Canadian here.
Posted By: dave1251

Re: MPG decrease in very cold weather?? - 01/11/20 07:28 AM

If you could get the drivetrain up to operating temperature quicker it would help with your fuel economy but being cold there are other things to worry about.
Posted By: pitzel

Re: MPG decrease in very cold weather?? - 01/11/20 07:45 AM

Originally Posted by dave1251
If you could get the drivetrain up to operating temperature quicker it would help with your fuel economy but being cold there are other things to worry about.


Assuming wear/damage isn't an issue, would it burn less fuel to immediately put significant load on the engine, to warm it up. Or idle it until it warms up and is more efficient?

It'll burn more fuel at the "significant load", but will warm up considerably faster at such point, the fuel consumption will drop rapidly.

Likewise, assuming the engine will start without a block heater, will cost incrementally more (or less) to partially heat the engine up with a block heater, than it would by simply starting it and burning an additional amount of fuel to warm it? The sort of temperature increase a block heater could achieve in an hour or two at -35, for example, likely pales in comparison with just literally a few seconds of engine operation and the heat created in the block due to combustion of the fuel.

I've personally mostly avoided using block heaters because if a car is in such condition that it won't start from the ambient cold without one (ie: due to weak battery, starter, etc.), I really don't want to be taking that vehicle anywhere that it can get cold and not start anyways. So its a matter of safety.

0W-xx oils, of course, mandatory in Canada.
Posted By: JLTD

Re: MPG decrease in very cold weather?? - 01/11/20 08:14 AM

All of the above, plus don't forget that before fully warmed you burn more fuel as well.
Posted By: dave1251

Re: MPG decrease in very cold weather?? - 01/11/20 08:31 AM

Also the drivetrain will wear less the faster operation temp is achieved without significant load of course.
Posted By: pitzel

Re: MPG decrease in very cold weather?? - 01/11/20 09:32 AM

Originally Posted by dave1251
Also the drivetrain will wear less the faster operation temp is achieved without significant load of course.


Well 'wear' can be a function of warm-up rates as well on certain kinds of parts, ie: gaskets that seal dissimilar metals.

There's lots of industrial equipment for which the manufacturers specify that warm-up rates shall not exceed certain values. Steam and gas turbines come to mind.

A drivetrain 'wearing out' faster may very well be justified in the context of fuel savings, or operational life limitations that are less than the probable in-service use of the equipment. ie: most cars made in the past 30 years were retired and destroyed with perfectly functional engines, but were removed from service due to accidents, technological obsolescence (ie: cash for clunkers, excess fuel consumption), or uneconomically repairable other components like interiors, transmissions, electronics, etc. Not bona fide mechanical engine wear.

Posted By: Duffyjr

Re: MPG decrease in very cold weather?? - 01/11/20 11:04 AM

Hard to say for sure without knowing what vehicle the OP is asking about but him saying slightly says it's normal.

My 08 Lucerne isn't as bad as my 99 LeSabre was which I think has to do with the fact the Lucerne warms up faster, both have the 3800. The Lucerne has dropped from 15.8 to 14.5 average according to the computer since winter started but that includes warm up time in the morning and sometimes at lunch depending on how cold it is, nice getting in a warm vehicle.The interesting thing to me is how fast the OLM has dropped since winter started.

I really don't want to talk about my 89 Sierra, it's to painful.
Posted By: Olas

Re: MPG decrease in very cold weather?? - 01/11/20 11:20 AM

Some curcumstances could cause this effect to go the other way based on the particular car in question.
Ffor example a heavily boosted small capacity engine equipped with knock control on low octane fuel could be overfuelling heavily in hot weather to control cylinder temps, but then during very cold weather the reduced IAT and increased intercooler efficiency would allow a leaner mix and so increased MPGs.

There are too many variables to apply a blanket rule here, its a case of 'suck it and see'
Posted By: joekingcorvette

Re: MPG decrease in very cold weather?? - 01/11/20 12:41 PM

Originally Posted by edyvw
Originally Posted by 2009Caraman
I'm kinda new to driving and was wondering what kind of penalty I can expect in extremely cold weather(-20c sustained)? Drives are typically 15mins or less.

I replaced my lower intake manifold gasket and though performance has returned fuel economy has slightly dropped. It's only been a 1/2 tank though and since i did the repair it's been at least -15c every day. I'd like to hear your thoughts or observations on mileage in the cold.

What car? What oil is in the car? Is it in garage?
Whatever you do, first few km's do not turn on heat and vent for 2-3km's as that delays warming up. Also, do not idle longer than necessary to put seatbelt, get accomodated. Move and move slowly, allowing transmission (assuming it is automatic) to [censored] around 2,000rpms.


Good info here. I had no idea turning on the heater would slow down engine warmup. Thank you.
Posted By: PimTac

Re: MPG decrease in very cold weather?? - 01/11/20 12:52 PM

Originally Posted by joekingcorvette
Originally Posted by edyvw
Originally Posted by 2009Caraman
I'm kinda new to driving and was wondering what kind of penalty I can expect in extremely cold weather(-20c sustained)? Drives are typically 15mins or less.

I replaced my lower intake manifold gasket and though performance has returned fuel economy has slightly dropped. It's only been a 1/2 tank though and since i did the repair it's been at least -15c every day. I'd like to hear your thoughts or observations on mileage in the cold.

What car? What oil is in the car? Is it in garage?
Whatever you do, first few km's do not turn on heat and vent for 2-3km's as that delays warming up. Also, do not idle longer than necessary to put seatbelt, get accomodated. Move and move slowly, allowing transmission (assuming it is automatic) to [censored] around 2,000rpms.


Good info here. I had no idea turning on the heater would slow down engine warmup. Thank you.





This must be a older car? I haven’t taken precautions like that in a long long time.
Posted By: jbutch

Re: MPG decrease in very cold weather?? - 01/11/20 12:59 PM

Not sure if it was mentionned before but colder air = more oxygen, so the MAF will be reporting denser air and the ECU will compensate by sending more fuel in the mix so that the engine does not run lean.
Posted By: ARCOgraphite

Re: MPG decrease in very cold weather?? - 01/11/20 02:13 PM

I get nearly 8 mpg less in the winter. ( 41 > 33 )

There is less energy density in the fuel ( more light fractions, volatiles)

The gear lubes in the diff and final and transmission are very viscous

the wheel bearing grease is very thick

Engine coolant is very cold

Engine will run in enrichment longer and at the slightest throttle tip in

and of course, the engine oil is extremely viscous.

Best you can do would be to run a block and pan heater 2-3 hours before startup

and block off 70-80% of the radiator.

And of course run the lightest real synthetic PAO oil allowed
and the lightest gear oil allowed.
Posted By: Triple_Se7en

Re: MPG decrease in very cold weather?? - 01/11/20 02:52 PM

Originally Posted by 2009Caraman
I'm kinda new to driving and was wondering what kind of penalty I can expect in extremely cold weather(-20c sustained)? Drives are typically 15mins or less.

I replaced my lower intake manifold gasket and though performance has returned fuel economy has slightly dropped. It's only been a 1/2 tank though and since i did the repair it's been at least -15c every day. I'd like to hear your thoughts or observations on mileage in the cold.

Real cold weather affects almost everything. It even affects slow transportation, like daily walks in below freezing temps. Our breathing gets affected during brisk walks in cold temps, which in-turn affects our oxygen level in our lungs.
You get less MPG. I get less TWO OH'.....lol

My dog never complains during those long walks thou. But he didn't smoke menthol cigs for one-half of his life either.....
Posted By: Quattro Pete

Re: MPG decrease in very cold weather?? - 01/11/20 02:59 PM

Originally Posted by PimTac
This must be a older car? I haven’t taken precautions like that in a long long time.
It applies to all cars/engines, old or new. In cold weather, on a cold engine there is little heat to go around. If you take it away from the engine by pumping it into the cabin, then the engine will take longer to heat itself up.

That's why automatic HVAC systems wait a while before ramping up heat blowing in cold weather on a cold engine.

Posted By: Jackson_Slugger

Re: MPG decrease in very cold weather?? - 01/11/20 03:34 PM

Another factor is driving through significant snow accumulation, I find that kills mileage the most...
Posted By: PimTac

Re: MPG decrease in very cold weather?? - 01/11/20 04:10 PM

Originally Posted by Quattro Pete
Originally Posted by PimTac
This must be a older car? I haven’t taken precautions like that in a long long time.
It applies to all cars/engines, old or new. In cold weather, on a cold engine there is little heat to go around. If you take it away from the engine by pumping it into the cabin, then the engine will take longer to heat itself up.

That's why automatic HVAC systems wait a while before ramping up heat blowing in cold weather on a cold engine.





Good point. I guess that’s why modern cars are electrified all around with heated windows and mirrors and heated seats and steering wheel. You don’t notice that cold air blowing as much when your bum is toasty.
Posted By: maxdustington

Re: MPG decrease in very cold weather?? - 01/11/20 04:45 PM

Originally Posted by edyvw
Whatever you do, first few km's do not turn on heat and vent for 2-3km's as that delays warming up. Also, do not idle longer than necessary to put seatbelt, get accomodated. Move and move slowly, allowing transmission (assuming it is automatic) to [censored] around 2,000rpms.
Move somewhere cold and try that. Everyone always says not to idle to warm up forget that you need to see out of your windshield in order to drive your car. What are you expected to do, drive slowly with the windows down until your car heats up? You can't drive slowly like that if you live anywhere near a city.
Posted By: hummdrumm

Re: MPG decrease in very cold weather?? - 01/11/20 05:45 PM



Originally Posted by JLTD
All of the above, plus don't forget that before fully warmed you burn more fuel as well.


This. It may be altitude as well. But consider two extremes in different climates. I have lived in LV and Great Falls. In LV my daily commute around 20 miles at 45 degrees. GF between 10 to minus where ever. Low for me in in 7 years -38 and 4 miles daily. Another factor was auto start which I didn’t have. Friends that had it often set theirs for 2, sometimes 3 starts a night
Posted By: RDY4WAR

Re: MPG decrease in very cold weather?? - 01/11/20 06:07 PM

Originally Posted by maxdustington
Originally Posted by edyvw
Whatever you do, first few km's do not turn on heat and vent for 2-3km's as that delays warming up. Also, do not idle longer than necessary to put seatbelt, get accomodated. Move and move slowly, allowing transmission (assuming it is automatic) to [censored] around 2,000rpms.
Move somewhere cold and try that. Everyone always says not to idle to warm up forget that you need to see out of your windshield in order to drive your car. What are you expected to do, drive slowly with the windows down until your car heats up? You can't drive slowly like that if you live anywhere near a city.


There's products out there that work very well at preventing fogging/frosting on the inside of the windshield. A good waxing of the windshield helps keep the frost on the outside from setting up too much. A pot of cold water takes care of what's left. This is what I did when I lived in Ohio, and it worked fine. I would always wait until the temp needle started to move before I turned on the heater. It would only blow cold air before that point anyway.
Posted By: 4WD

Re: MPG decrease in very cold weather?? - 01/11/20 06:11 PM

Originally Posted by Jackson_Slugger
Another factor is driving through significant snow accumulation, I find that kills mileage the most...


HaHa … same with mud and sand …
Posted By: barryh

Re: MPG decrease in very cold weather?? - 01/11/20 10:43 PM

Here's 12 years of data which if you ignore a slight rising trend shows a regular as clockwork 10 MPG or 15% swing between summer and winter on my air cooled motorcycle. With no control of cooling, air cooled engine's never really get up to temperature in the winter so I would expect a water cooled engine to fair a little better.

[Linked Image]
Posted By: fdcg27

Re: MPG decrease in very cold weather?? - 01/12/20 12:00 AM

So you're looking at around -4F?
I'd expect a very noticeable increase in fuel consumption, in the range of 10-20% or at least that's what I've come to expect with various vehicles over the years.
At that kind of start temperature, I'd surely let the thing idle at least ten minutes prior to setting out if only for the comfort of the driver.
That's what I do, since I don't intend to layer up as I do for a planned extended time outdoors in the cold just for the drive to work.
There's also the need to have enough heat available to avoid the moisture in your breath freezing on the windows.
Posted By: BrianF

Re: MPG decrease in very cold weather?? - 01/12/20 12:10 AM

Ball park with my trailblazer I was running about 12.6 L/100km in the summer. Come this cold winter I average around 15. Yes there is more idle time included but there is nothing I can do about it.
Posted By: 2009Caraman

Re: MPG decrease in very cold weather?? - 01/12/20 03:33 AM

OP here. Thanks for the comments. Vehicle is a 3.3l 2009 Caravan. After doing some math it seems it has fallen 2 mpg since the deep freeze started. Nothing crazy so I will take it as it is.

These vans are pretty bad on fuel to begin with. Went from 17mpg to 15mpg is all. All city stop and go driving.
Posted By: painfx

Re: MPG decrease in very cold weather?? - 01/12/20 05:15 AM

Yes it does. Especially with the winter blended gasoline.
Posted By: Pew

Re: MPG decrease in very cold weather?? - 01/12/20 07:00 AM

Originally Posted by Quattro Pete
Originally Posted by PimTac
This must be a older car? I haven’t taken precautions like that in a long long time.
It applies to all cars/engines, old or new. In cold weather, on a cold engine there is little heat to go around. If you take it away from the engine by pumping it into the cabin, then the engine will take longer to heat itself up.

That's why automatic HVAC systems wait a while before ramping up heat blowing in cold weather on a cold engine.



Mine doesn't even warm up to operating temps once the temps dip below freezing unless I start going up hills. Mileage drops a good 5 MPGs.
Posted By: Railrust

Re: MPG decrease in very cold weather?? - 01/12/20 01:56 PM

I tend to drop at least 2 mpg's as soon as the weather turns cold where I am (usually November till March).

I attribute it to the colder air density, and the computer having to add more fuel to keep the air fuel ratio 14.7 to 1. Could be wrong.
Posted By: kschachn

Re: MPG decrease in very cold weather?? - 01/12/20 04:10 PM

Here is an article from Scientific American, kind of old but probably still relevant:

https://www.scientificamerican.com/article/why-is-the-fuel-economy-o/
Posted By: Bryanccfshr

Re: MPG decrease in very cold weather?? - 01/12/20 05:15 PM


Colder weather means a vehicle has to overcome
Thicker engine oil, thicker transmission fluid or oil/ thicker transaxle or differential oil.

The shorter the trip the more the impact cold weather will have on overall MPGs. As the fluids may never actually get up in temperature.

Additionally more accessories are used, defrost, heaters, seat heaters etc drawing more power.

At highway speeds you deal with more wind drag from denser air and the cold air flowing keeps the differentials cooler, meaning it would never be as efficient as on a warm day,

All of these inefficiencies mean More fuel is burned and that is why many locales require oxygenates to deal with the air quality issues that causes in denser areas.
Posted By: edyvw

Re: MPG decrease in very cold weather?? - 01/13/20 04:05 AM

Originally Posted by maxdustington
Originally Posted by edyvw
Whatever you do, first few km's do not turn on heat and vent for 2-3km's as that delays warming up. Also, do not idle longer than necessary to put seatbelt, get accomodated. Move and move slowly, allowing transmission (assuming it is automatic) to [censored] around 2,000rpms.
Move somewhere cold and try that. Everyone always says not to idle to warm up forget that you need to see out of your windshield in order to drive your car. What are you expected to do, drive slowly with the windows down until your car heats up? You can't drive slowly like that if you live anywhere near a city.

Really? I regularly park at -20c below while ski, sometimes overnight at parkings and it reaches to -35c occasionally. I live 1.30hrs from the coldest area in lower 48, South Park basin. Now, if I have kids with me, that is different story. But if not, I start it, get adjusted and off to go. If ice on the car, I scrape it.
Posted By: edyvw

Re: MPG decrease in very cold weather?? - 01/13/20 04:16 AM

Originally Posted by PimTac


This must be a older car? I haven’t taken precautions like that in a long long time.

I do that with every car. Especially with two small kids. In VW I need to keep it on cold and no vent for a 1-2 miles, and after will have good heat. Same with BMW. Sienna is hopeless case even with block heater.
Turning heat on and than ventilation, you are basically cooling down coolant that is going through heater core. I tell visitors here when they drive to the Pikes Peak: Turn off A/C, turn on heat to max and vent to max, otherwise you might be overheating somewhere at 13,000ft.
Posted By: supton

Re: MPG decrease in very cold weather?? - 01/13/20 01:52 PM

What's so hard about an ice scraper and cracking a window? That is what I do, unless if there was a storm and I have an inch of ice; in that case yeah I'll let it idle so as to soften the ice. But for frost? scrape and motor off.

I leave the heat off until I see the temp gauge move. Is it hurting anything to turn the heat on full blast right after getting in? Nope. Technically the heater core acts like a mini-radiator (same principle) only the real radiator has a thermostat that won't open when the coolant is below a temperature around boiling--but the heater core gets coolant always, so turning on the heater fan is going to slow down engine heating up. Does it really matter? I'm not sure--the engine will warm up faster with it off, but once on, it's still drawing heat away, so I'm not sure it matters... me, I just don't want cold air blowing on me, so I wait until I know it'll be warm air blowing on me.

My truck drops mpg badly in winter. I drove it year round once and could hit 20 mpg, 21 even, in summer. Snow tires and winter dropped it to 16 mpg. Although now that I drive it little it seems to get 16 year round... my other cars will drop in cold weather but it seems like, if it's above 20F I don't have much of a change. But for me, a short trip is 15 minutes, most trips are much longer--once up to temp, winter losses are not massive.

IIRC winter blend gas often has a bit less Btu's per gallon, so there's something like up to 5% there (but it varies with the blend).
Posted By: edyvw

Re: MPG decrease in very cold weather?? - 01/13/20 06:57 PM

Originally Posted by supton
What's so hard about an ice scraper and cracking a window? That is what I do, unless if there was a storm and I have an inch of ice; in that case yeah I'll let it idle so as to soften the ice. But for frost? scrape and motor off.

I leave the heat off until I see the temp gauge move. Is it hurting anything to turn the heat on full blast right after getting in? Nope. Technically the heater core acts like a mini-radiator (same principle) only the real radiator has a thermostat that won't open when the coolant is below a temperature around boiling--but the heater core gets coolant always, so turning on the heater fan is going to slow down engine heating up. Does it really matter? I'm not sure--the engine will warm up faster with it off, but once on, it's still drawing heat away, so I'm not sure it matters... me, I just don't want cold air blowing on me, so I wait until I know it'll be warm air blowing on me.

My truck drops mpg badly in winter. I drove it year round once and could hit 20 mpg, 21 even, in summer. Snow tires and winter dropped it to 16 mpg. Although now that I drive it little it seems to get 16 year round... my other cars will drop in cold weather but it seems like, if it's above 20F I don't have much of a change. But for me, a short trip is 15 minutes, most trips are much longer--once up to temp, winter losses are not massive.

IIRC winter blend gas often has a bit less Btu's per gallon, so there's something like up to 5% there (but it varies with the blend).

Dramatically! Also depends on the vehicle, but it will slow down arm up process.
Posted By: DGXR

Re: MPG decrease in very cold weather?? - 01/13/20 08:04 PM

My thoughts... Engines warm up quicker when they are driven gently, significantly faster than just idling. Allow at least 30 seconds for the oil to circulate, and however long it takes the fast idle to come down so the transmission doesn't lurch when you engage the gear. Also make sure the windows are clear before you drive away (obvious, but need to say). Because your engine doesn't get so cold in summer, it will reach full temp quicker and you will notice a significant increase in fuel economy... all else being equal.
Don't put a heavy load on a cold engine, or rev it too high. (I keep mine below ~3000 rpm until it's nearly full temp.) Do some research on open loop/closed loop operation. Seasonal fuel blends, if there is such a thing in your region, will have an effect on fuel economy.
Posted By: emg

Re: MPG decrease in very cold weather?? - 01/16/20 05:09 AM

Originally Posted by joekingcorvette
Good info here. I had no idea turning on the heater would slow down engine warmup.


Our Forester will ramp up the engine rpms when the heater is on and the engine is cold (which seems to mean it's under 70-80C). Instead of a typical 1200rpm in city driving, it sits at 2000rpm.

This means I get about the same mpg in winter as I would in summer, so long as I keep the heater off. But that's only an option down to about -20C, then the mpg drops about 30% due to the higher rpms with the heater on.

It's really quite bizarre to see the engine rpms rise when I take my foot off the gas and it shifts from acceleration mode to warming the engine up mode.
Posted By: Miller88

Re: MPG decrease in very cold weather?? - 01/17/20 02:50 PM

My 2011 Focus was real bad. On a cold start, that engine was going to run at 2500 - 3000 RPM. It didn't matter or care what you were trying to do. I could drive it part of the way to work without touching the gas pedal (in some cases, I'd have to hit the brake on the road because it would try to maintain 3000 RPM in gear). Also made it hard to shift in the cold. I'm sure it didn't help the pilot bearing that failed.

I really like the way my Subaru Forester 6MT handles it. It does the fast idle thing, but once it realizes you're moving, it will idle down normally and doesn't rev back up when I'm trying to shift or at a stop light.

The 17 Leaseon Sentra will idle less than 1500 RPM, but the CVT holds the revs at 2000-2500 when cold driving around.

Higher idle is only part of it. Gear oil , transmission oil and such contribute to it. And longer on a richened fuel mixture. I have 3 differentials in the Subaru running 75w-90 that have a ton of resistance in the cold. I can definitely feel it.
Posted By: pitzel

Re: MPG decrease in very cold weather?? - 01/22/20 08:09 PM

Okay some real world data. Drove Regina to Minneapolis at 50mph. Normally my car gets 38 USmpg in the summertime on those roads and at those speeds. In -30C weather last week, the efficiency was reduced to 34 USmpg. Car hasn't had its oil changed in 100k km's (~62k miles), but using 0W-30 oil (which has probably thickened to a -40 oil).

GM 3.1L V6 (LH0 engine) / 4T60 transmission. Heater running full blast for the first hour or two, and then gradually throttled back as everything inside the car was toasty warm.

Posted By: road_rascal

Re: MPG decrease in very cold weather?? - 01/22/20 08:17 PM

Originally Posted by pitzel
Car hasn't had its oil changed in 100k km's (~62k miles), but using 0W-30 oil (which has probably thickened to a -40 oil).





Say what now?
Posted By: pitzel

Re: MPG decrease in very cold weather?? - 01/22/20 10:06 PM

Originally Posted by road_rascal
Originally Posted by pitzel
Car hasn't had its oil changed in 100k km's (~62k miles), but using 0W-30 oil (which has probably thickened to a -40 oil).


Say what now?


Documented in other threads... Complete with pictures of both the oil pan removed (oil drained and refilled) as well as valve covers removed.
Posted By: circuitsmith

Re: MPG decrease in very cold weather?? - 01/23/20 06:37 PM

Originally Posted by pitzel
Normally my car gets 38 USmpg in the summertime on those roads and at those speeds. In -30C weather last week, the efficiency was reduced to 34 USmpg.


I figure the difference in air density and wind resistance is a big chunk of that.
From -30C to 25C is more than 10% air density change.
Posted By: Cujet

Re: MPG decrease in very cold weather?? - 01/23/20 07:25 PM

Originally Posted by JLTD
All of the above, plus don't forget that before fully warmed you burn more fuel as well.


There are a number of reasons for this.

1) The air/fuel ratio must be richer (more fuel) when the engine is cold, this compensates for lack of fuel vaporization.
2) The cold engine has thicker oil and more internal friction
3) The cold engine transfers more of the heat of combustion into the cold metal parts, instead of expanding the air and pushing the pistons down.
Posted By: RDY4WAR

Re: MPG decrease in very cold weather?? - 01/23/20 07:52 PM

Originally Posted by Cujet
Originally Posted by JLTD
All of the above, plus don't forget that before fully warmed you burn more fuel as well.


There are a number of reasons for this.

1) The air/fuel ratio must be richer (more fuel) when the engine is cold, this compensates for lack of fuel vaporization.
2) The cold engine has thicker oil and more internal friction
3) The cold engine transfers more of the heat of combustion into the cold metal parts, instead of expanding the air and pushing the pistons down.


Yep. I'm part of a big group of 80s-90s Mustang owners and regularly see people replacing the OEM 192°F thermostat with a 160°F stat and no tuning changes. For the OBD-I cars, it doesn't initiate closed loop until ~175°F. You can tune it to changeover sooner, but most don't. They only pickup +2-4 hp and lose -2-5% in fuel economy. The few I got to do a UOA after 4-6k miles all had >2% fuel dilution despite mixed highway / long trips. The car nevers gets out of open loop and keeps dumping fuel trying to heat the engine up.

To make matters worse, several insist on staying away from ethanol blended fuel and only use ethanol-free 93 aki fuel which has a higher boiling point and lower RVP compared to E10 which only makes vaporization worse.
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