Temperature and Fuel Economy

I've seen discussion on here lately about colder temperatures affecting fuel economy. I just wanted to throw in my two cents worth.

The setup: I've got a ScanGauge E that shows exact coolant temp. I live in Central Ohio, where it's been about 10-15 degrees F. I have an engine block heater that I use whenever I can (unrelated to this post, I just love my block heater is all :) ).

The observation: With the cabin temp set to 68 to 70, and on auto, it eventually ramps up the fan pretty fast. If I leave it on auto, the fan speed stays high, and my coolant temp wont get up to 195F. If it's cold enough, the cabin fan blowing through the heater core pulls enough heat out of the coolant to prevent the engine from reaching full temp.

It would seem to me that an engine not operating at its' optimal temperature, would use more fuel. Might be worth bundling up a little more, turning off auto temp, and lowering the cabin fan speed. Thoughts?

Gathering data like this helps. Thanks - it all makes sense to me.

I suppose I should have said what temp it does stay at. :) Since it depends on outside temp, cabin fan speed, and how I'm driving, it seems to hover anywhere from 130 to 150. With the cabin fan lower, or off, it does get up to full temp.

Is your grill blocked?
What are intake air temps?
Can this be captured and graphed?

No grill block yet. I'm wanting to do it nice.

I'm pretty sure the ScanGauge shows air intake temps, I'll have to find it.

As far as I know, the ScanGauge doesn't capture it. At least not that I'm aware of. If I had the time, it'd make a fun Arduino project. :)

When I worked at a dealership for 30 plus years, we all would just shake our head at any fuel economy talk in the winter months. Just be comfortable and whatever milage you get, is what you get. Bearings turn harder, longer warm up times, fuel can be different, rear defroster electrical load, it goes on and on.

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Originally Posted by flatbroke

When I worked at a dealership for 30 plus years, we all would just shake our head at any fuel economy talk in the winter months. Just be comfortable and whatever milage you get, is what you get. Bearings turn harder, longer warm up times, fuel can be different, rear defroster electrical load, it goes on and on.

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Excellant point! Just told my wife, almost the same thing yesterday. She has a 2013 CMAX hybrid, and was bummed because her mileage is dropping.

FYI... A Scangauge does show air intake temperature. It's usually one of the 4 gauges I have displayed on mine. :)

As a general rule, I have noticed that the air intake temperature normally runs about 7-10 degrees above the ambient temperature. This car pounds the fuel when the outside temps are really cold. I can't imagine the mileage some of you guys are seeing who regularly drive in sub-zero temps! :eek:

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Originally Posted by flatbroke

When I worked at a dealership for 30 plus years, we all would just shake our head at any fuel economy talk in the winter months. Just be comfortable and whatever milage you get, is what you get.

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Disagree! Too fatalistic for my liking. :D

There are lots of things you can do to help minimize the cold weather fuel economy penalty, eg. off the top of my head:

• Don't idle the car to warm it up.
• Install & use a block heater (arguably extends engine life, too).
• Make sure tire pressure is kept up (many people forget/don't know that pressure falls with ambient temps -- I see more cars driving around on half-flat tires in early winter than any other time).
• Turn off the A/C compressor if you don't need it when using the "defrost" setting.
• Make a partial or full grille block (how much depends on your individual circumstances; aerodynamic benefit as well as thermal management benefit).
• Avoid doing many short trips where the vehicle never warms up fully; combine trips if possible.
• Make sure snow/ice is fully cleaned from the car (can be a significant drag penalty at higher speeds - increases both frontal area and drag coefficient).
• Use synthetic lubricants wherever possible, engine, transmission, etc. (viscosity is more stable vs. conventional lubricants which dramatically thicken in freezing temps).
• Really pay attention to your highway speeds: aero drag is proportional to both speed as well as air density. You burn more fuel per each MPH increase in cold, dense winter air than in warm summer air.
• Choose a manual transmission when buying. It avoids the extended warm-up penalty that automatics experience (forced higher engine RPM until a certain coolant temp is reached).

OK, so doing these things won't permit anyone to match their summer MPG in the freezing cold, but they will help atleast keep the seasonal difference to a minimum.

Adding a warm air intake shortens the time it takes to get your motor up to operating temperature, and it works very well with a grille block.

Good point - I forgot that one.

I always thought it was the winter gas blend that had the biggest effect on mileage. Wonder if I need to re-think that. One thing I have noticed with Mirage vs other cars I've had, mileage does take a bigger hit with little things like use of AC. And changing to winter tires (blizzak ws80's) dropped the mileage by about 6-8 MPG. I'll live with that because the blizzaks are so much better in winter driving. There is absolutely no need for AWD with those babies installed. But that's another topic ��.

It's a common reason given, but winter gas has only a few percent less energy content than summer fuel. It's just one of many factors.

I suppose you could stockpile summer gas, but if it gets really cold where you live, the car might not run as well!

Here's a bit more detail, from my drive this morning.

• Outside Temperature, 5F.
• Car parked outside overnight.
• Engine block heater on for ~2 hours beforehand.
• Water temp when turned on, 57F. Air intake temp was low 30s, possibly due to pre-warmed engine?
• Still no grill block.
• Climate control set on 70.
• By 3/4 mile down the road, water temp was about 110.
• Air intake temp is around 20F and stays there for the duration of the trip.
• By 2 miles down the road, water temp was about 140.
• By this time, fan is on about 6 bars.
• From about mile 3 to mile 5, water temperature hovers right around 150-155.
• At mile 5, I hit the off button on climate control.
• Water temperature climbs slowly but steadily to around 190 by the time I pull into my parking space, after a total of 5 1/2 to 6 miles.

It seems logical to me. The Mirage engine uses less fuel than a larger engine. Less fuel = less byproduct (wasted heat). Less wasted heat = less heat to remove from the coolant. Combine that with much colder temperatures, and you've got an engine that sacrifices more heat from the coolant for the cabin warming process than other vehicles with larger engines. Result is poorer cold weather gas mileage, since the engine can't get the optimum operating temperature. I still got 37mpg on a short, cold trip, so I can't complain too much. :)

Just filled up again yesterday and have to say that milage has been consistently down by 20% from around 44 MPG to 33 MPG as measured at the pump, not the trip computer. It's been this way for 2 or 3 tanks. Winter gas, cold temps, change to snow tires have caused a big hit. Conditions for the last tank were colder than normal conditions, but clear weather and clean roads with temps in the mid-20's. The tires are Blizzaks. Perhaps I should also add that said tires are over sized which would help by reducing cruising RPM's but perhaps hinder by making total miles driven appear normal than actual miles. Yes, our little Mirage can get some great MPG numbers, but it seems to be more adversely affected (effected?) by less than ideal conditions than other cars I've owned.

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Originally Posted by Ranny

Just filled up again yesterday and have to say that milage has been consistently down by 20% from around 44 MPG to 33 MPG as measured at the pump, not the trip computer. It's been this way for 2 or 3 tanks. Winter gas, cold temps, change to snow tires have caused a big hit. Conditions for the last tank were colder than normal conditions, but clear weather and clean roads with temps in the mid-20's. The tires are Blizzaks. Perhaps I should also add that said tires are over sized which would help by reducing cruising RPM's but perhaps hinder by making total miles driven appear normal than actual miles. Yes, our little Mirage can get some great MPG numbers, but it seems to be more adversely affected (effected?) by less than ideal conditions than other cars I've owned.

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Yes to all of the above and don't forget using the defrost button runs the a/c compressor also. Use of a block heater has been shown to have positive effects with better mileage and also blocking a portion of the lower grill. Members with scan gauges have reported that the Mirage has ample grill area with water temps struggling to get over 180 degrees during cold weather before blocking a portion of the lower grill.

Yes, am aware of that the compressor runs with defrost. Our little car is so light, I sometimes turn on the compressor going down hill to add a bit of extra braking. Mine is garage kept, so I'm not sure adding the block heater would help much.

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Originally Posted by Ranny

Yes, am aware of that the compressor runs with defrost. Our little car is so light, I sometimes turn on the compressor going down hill to add a bit of extra braking. Mine is garage kept, so I'm not sure adding the block heater would help much.

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I've used the compressor for braking too! Grill blocking with foam might be helpful though. Just nice and soggy down here on the coast although we did get some frost a few days in a row and there was snow for a day!

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Originally Posted by Ranny

Mine is garage kept, so I'm not sure adding the block heater would help much.

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It does. Other forum members here even use their block heaters in warm weather.

As I recall, modern block heaters just install near a freeze plug? 'Back in the day', when I lived in northern Vermont and drove a '65 Buick Skylark, the block heater was spliced into one of the coolant system hoses. And in those conditions, with a car as primitive as the Skylark, a block heater was a must.

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Originally Posted by Ranny

As I recall, modern block heaters just install near a freeze plug? 'Back in the day', when I lived in northern Vermont and drove a '65 Buick Skylark, the block heater was spliced into one of the coolant system hoses. And in those conditions, with a car as primitive as the Skylark, a block heater was a must.

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Block heater for the Mirage is super easy to do. It's a cartridge type. Here is a dedicated thread to installation.

http://mirageforum.com/forum/showthr...r-Installation

I would just like to note that even though its well known that the cold weather will adversely impact fuel consumption performance, I haven't seen as stark of a difference on any vehicle as I have on the Mirage. My old Sentra would maybe increase 0.5-1 L/100 km, other vehicles in my household would increase 1-2 L/100 km. The Mirage almost doubles with around 4-5 L/100 km. And this doesn't start in the negative temperatures; it starts in the fall.

Now to be fair, the base fuel consumption is exceptional, so even the increase to 8-9 isn't really bad, but the tank holds very little so I find myself out at gas stations in the cold more than I would like :p

I have bought a block heater, And am going to run like a 19 meter cable from my apartment. Hopefully that helps.

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Originally Posted by Spadesheart

...even though its well known that the cold weather will adversely impact fuel consumption performance, I haven't seen as stark of a difference on any vehicle as I have on the Mirage.

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I tend to agree.

My fall mileage dropped off slightly (by maybe 3%) with no change in outside temps. I figured that's when winter fuel blends started showing up at the fuel pumps.

When single-digit outside temps started occurring regularly...my mileage figures dropped close to 15%...or about 8 mpg! :nightmare:

If you're driving in near-zero temps on a regular basis, your mileage is getting hammered. And it seems like many of you guys up north are running snow tires...which also isn't helping.

I'd say 15% is a very common number to see. It just seems larger when you have a car that gets 40+ mpg vs 15 mpg.

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Originally Posted by Daox

...15% is a very common number
...It just seems larger when you have a car that gets 40+ mpg vs 15 mpg.

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That is a great point to keep in mind. :o

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Originally Posted by Spadesheart

I would just like to note that even though its well known that the cold weather will adversely impact fuel consumption performance, I haven't seen as stark of a difference on any vehicle as I have on the Mirage.

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I agree.

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Originally Posted by Spadesheart

The Mirage almost doubles with around 4-5 L/100 km. And this doesn't start in the negative temperatures; it starts in the fall.

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Double? Wow. In autumn? Wow again.

I haven't experienced this myself, thankfully.

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Originally Posted by wellswebdesign

Here's a bit more detail, from my drive this morning.

• Outside Temperature, 5F.
• Car parked outside overnight.
• Engine block heater on for ~2 hours beforehand.
• Water temp when turned on, 57F. Air intake temp was low 30s, possibly due to pre-warmed engine?
• Still no grill block.
• Climate control set on 70.
• By 3/4 mile down the road, water temp was about 110.
• Air intake temp is around 20F and stays there for the duration of the trip.
• By 2 miles down the road, water temp was about 140.
• By this time, fan is on about 6 bars.
• From about mile 3 to mile 5, water temperature hovers right around 150-155.
• At mile 5, I hit the off button on climate control.
• Water temperature climbs slowly but steadily to around 190 by the time I pull into my parking space, after a total of 5 1/2 to 6 miles.

It seems logical to me. The Mirage engine uses less fuel than a larger engine. Less fuel = less byproduct (wasted heat). Less wasted heat = less heat to remove from the coolant. Combine that with much colder temperatures, and you've got an engine that sacrifices more heat from the coolant for the cabin warming process than other vehicles with larger engines. Result is poorer cold weather gas mileage, since the engine can't get the optimum operating temperature. I still got 37mpg on a short, cold trip, so I can't complain too much. :)

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Can anyone chime in on optimum time for plugging in a block heater? Does it stop at a cretain temp? I really don't know much about how this thing works. I have mine on a timer and it switches on about 4hrs before I leave for work. Temp light shuts off about the time I turn out of the neighborhood onto the main road. It's been between 0F and 20F in the mornings here. I'm usually at about 40-44mpg by the time I get to work. 30 min drive.

Mine had been taking a big hit, normally I easily get 5.5-6.5L/100 no matter how hard I drive it, but in winter time (first winter with it), I'm struggling to even get 7.0L/100, sometimes if i drive really conservative or let it roll a lot, i may get 6.5L...

So that's roughly 20-25% hit... Are you guys sure that adding grill block to raise the temp up a bit would really help in the MPG??

Canada here, was minus 10 to minus 20c last few weeks.

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Originally Posted by theforerunner343

Can anyone chime in on optimum time for plugging in a block heater?

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Consider using it year 'round. It will help warm the motor oil up to operating temperature more quickly.

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Originally Posted by Eggman

I agree.


Double? Wow. In autumn? Wow again.

I haven't experienced this myself, thankfully.

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During the period that Codenamezero is speaking of, I was getting around 8- 8.5 L/100 km with hour long highway driving. Thats a far cry from the 4.5-5 of the summer.

When looking at short drives, the fuel economy does most certainly take that much of a hit come fall. Now I suspect that the block heater would fix the fall issue almost 100%, but still, that's an extraordinary leap. With long drives, I'm probably within the 3-10% range, as is consistent.

Winter can be called legitimately poor for short drives, and average for long drives without the block heater in regards to fuel economy. While I do have winter tires on, they were bought used and somewhat worn. That cant be accounting for this much of an issue. I do hope the block heater is as magical as it's been made out to be haha.

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Originally Posted by Spadesheart

I do hope the block heater is as magical as it's been made out to be haha.

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Yeah, read around for some member's experience with the heaters.

Here's 3dplane's detailed results on using a block heater.

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Originally Posted by 3dplane

I left the block heater plugged in over night. I figured it consumes about 30 cents worth of electricity doing that.
But in the morning I had frost on the roof of my house even though ambient temp was supposedly around 40°F.

I keep a small scanner in the glove box and I plugged it in to see coolant temp. ECT was 100°F to start my morning commute vs. I guess it would've been 40°F without the block heater.

The green cold coolant light went off in 0.5 miles from my house vs.2.5 miles on a cold morning like this. (I make it my goal to keep that green cold coolant light on as long a distance as I can from my house because even it seems contradictory I think it means I covered a longer distance on less fuel if it is still green at a certain waypoint than if it already went off before that point!?)

At the end of the first road I take (3 miles from house) I like to see the display just over 60 MPG.This morning it said 74.3 MPG!

Then I have to take a highway where I have to pick up the pace to match the speed of the 'wild idiots' :) where the MPG will drop until I get close to a town again but the block heater really gave me good head start so to speak.

When I get to work on a cold morning I usually see 60-62 MPG displayed and today it said 69.9 MPG!
(on a saturday with little traffic I am always 70+ despite the cold so still traffic/speed is the biggest MPG killer)

Besides the MPG it is better for the engine not to have to fight the cold!

Why did I not do this sooner? Thanks again for the info posted here guys!

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Click on the little blue arrows to read this post in the context of the thread it was originally posted in. I shouldn't make duplicate posts, but I think this one is pretty significant - not only in cold weather but in warmer weather too. :)

I've been meaning to do this myself. If you do this, please share your experience with us all.

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Originally Posted by theforerunner343

Can anyone chime in on optimum time for plugging in a block heater?
Does it stop at a certain temp?
I have mine on a timer and it switches on about 4hrs before I leave for work.

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After a certain amount of time, a block heater won't raise the temperature of the coolant any more.

Here's my observation from using it in a 35 degree garage. If I start the heater 3 hours before I drive the car, that's enough to raise the coolant temperature about 60 degrees above the surrounding temperature. When I start my car, I can see on my Scangauge that the coolant temp is close to 100 degrees. If I leave the heater plugged in longer than a few hours, the coolant temperature won't get any warmer.

If your car is parked outside in the winter, 4 hours is probably a good number to start with...unless the outside temperature is below zero. Then you might want to consider extending that time.

FYI...the little green temperature light on your dash goes off when the coolant temperature reaches 139 degrees. If you don't have a Scangauge, you can figure out how well your block heater is doing by watching how long it takes for that light to go off after you start the car in the morning.

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Originally Posted by wellswebdesign

I've seen discussion on here lately about colder temperatures affecting fuel economy. I just wanted to throw in my two cents worth.

The setup: I've got a ScanGauge E that shows exact coolant temp. I live in Central Ohio, where it's been about 10-15 degrees F. I have an engine block heater that I use whenever I can (unrelated to this post, I just love my block heater is all :) ).

The observation: With the cabin temp set to 68 to 70, and on auto, it eventually ramps up the fan pretty fast. If I leave it on auto, the fan speed stays high, and my coolant temp wont get up to 195F. If it's cold enough, the cabin fan blowing through the heater core pulls enough heat out of the coolant to prevent the engine from reaching full temp.

It would seem to me that an engine not operating at its' optimal temperature, would use more fuel. Might be worth bundling up a little more, turning off auto temp, and lowering the cabin fan speed. Thoughts?

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I have driven dozens of times the same 50 km of flat highway, at the same speed (90 km/h) under the same wind conditions, in two directions, with tyre pressure at the prescribed level and with the same person (me) on board. In all cases, the inside temperature was set at 21 C with the heater on Auto. The only difference was the ambient temperature and the fact that in winter I use the front and mirrors and rear defrost at the first 4 km. The first was +15 C and the second was 0 C. I noticed a 15% decrease in fuel economy in the winter on that highway in my Mirage. I am happy with that. It is kind of funny that (if you use Celsius scale) the fuel economy changes by 1% for every degree change in ambient temperature.

Compared to other vehicles I had in the past (with bigger engines) that is very good. The laws of thermodynamics hold, therefore! And, on topic, I see no indication that the heater draws away too much heat from the engine. But these tests were of course not really suited to measure that.

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Originally Posted by RodeRoNL

I have driven dozens of times the same 50 km of flat highway, at the same speed (90 km/h) under the same wind conditions, in two directions, with tyre pressure at the prescribed level and with the same person (me) on board. In all cases, the inside temperature was set at 21 C with the heater on Auto. The only difference was the ambient temperature and the fact that in winter I use the front and mirrors and rear defrost at the first 4 km. The first was +15 C and the second was 0 C. I noticed a 15% decrease in fuel economy in the winter on that highway in my Mirage. I am happy with that. It is kind of funny that (if you use Celsius scale) the fuel economy changes by 1% for every degree change in ambient temperature.

Compared to other vehicles I had in the past (with bigger engines) that is very good. The laws of thermodynamics hold, therefore! And, on topic, I see no indication that the heater draws away too much heat from the engine. But these tests were of course not really suited to measure that.

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Wow, that's very through, and I would say consistent with my experience. Have you driven well into the negatives though?

Highway driving is passable, that isn't the main issue, though it most certainly could be better. City driving or short drive economy is quite bad, and that's really sad. It's consistently below -10 where i am.

I do not envy your weather :/
In Portugal, it's winter atm and we are having bright sunny days with temperatures around 15ºC :D one of the reasons i didn't leave my country is this beautiful weather :)

Where I live it is never much colder than 0C. Something with very close to the warm gulf stream....

In fact it is now -5 C which is nowadays unusually cold. It used to be colder when I was young (climate change). However, unlike you I enjoy the cold weather a lot when there is no wind. If there is wind, it is really bad. I live very close to the sea, so the air is moist. That gives an extra boost to the cold feeling when windy.