Fuel Econmony Hit in Winter

[Ian Williams]

Does anyone have a rule of thumb for how much your mileage goes down as it gets colder?

Like X mpg for Y Temp

[allan5oh]

I don't know, but close to a full mpg here. We're talking from 70-80 degrees to -10 or so F. every 10 F is about .1 mpg. Of course that depends on wind too. Once it gets real cold that wind really can pound you.

[wot i life]

My old boss in Wales said that by fitting wind deflectors on the truck, he reduced fuel consumptiom by 5%. I,m no engineer and I don,t know much about drag co-effecient, but I do know he wouldn,t lie about that. :wink:

[Dejanh]

I hauled 5000LB load from L.A. to Chicago and burned about the same amount of fuel as i would hauling a 45000 due to wind.....i just hate driving while windy but dont have a choice..

[bob h]

The slight increase in air density is a factor, but the main cause of fuel economy loss (up to about 1 mpg) in winter is due to lower btu content of winter fuel... not the temperature.

[solo379]

10-15% is about a norm. Lot's of factors, winter blend, air density, longer time to get to "operating" temperature(tranny, axles..)...

[yoopr]

no rule of thumb from me but I always expected from a 1/2 to a gallon mpg decrease

[xzostd1]

The slight increase in air density is a factor, but the main cause of fuel economy loss (up to about 1 mpg) in winter is due to lower btu content of winter fuel... not the temperature.

Isn't our new ULSD also supposed to cause lower fuel economy?(I think I had read 2-3%)
Bill

[allan5oh]

No, it's mostly due to the air. I run #2 a lot in winter, and it doesn't make a huge difference. Maybe 10-15% compared to the cold weather. It does make a difference though.

There's also the extra friction from the tires hitting the pavement, diffs being cold, transmission cold, all the wheel bearings are stiff.

[bob h]

quote="allan5oh"No, it's mostly due to the air.

I believe it's as much (or more) due to idling and cold engine operation IMO

I run #2 a lot in winter,

If you're running #2 in the winter, you must be way farther south than me... if you don't run blended winter fuel here, you'll freeze up

and it doesn't make a huge difference. Maybe 10-15% compared to the cold weather.

could you elaborate on this statement, not sure what it means? maybe i'm still asleep ;0)

It does make a difference though.

There's also the extra friction from the tires hitting the pavement, diffs being cold, transmission cold, all the wheel bearings are stiff.

we have had mild ambient temps here up until about 3 weeks ago (rarely went below 30 degrees), since then the temps have plumetted and stayed cold (rarley rises above 5 degrees)

my fuel mileage has not changed significantly since the temp change... however, it did change more significantly when the winter fuel started being delivered in the fall (over 1/2 mpg)

[allan5oh]

But one thing though... our diesels actually become more efficient when its colder out. Easiest way to tell is how much power it has. It's never going to inject "more" fuel at WOT+full boost. It always injects the same. If it pulls harder in winter, it's creating more horsepower with the same fuel. It becomes more efficient.

However, you're right when you compare the two one day to the next. I was talking overall, in winter the big difference is the extra friction and air resistance.

I just got back from a trip, I fueled up with #2 in Minnesota. It's -35 with the windchill here. I would never run more then 50% #2 when it's this cold. Hell, it even has that 2% biodiesel crap. No problems. Still not much of an improvement in fuel mileage compared to the Canadian fuel I had in there. I think I went from 5.8 to 6.5. But I also went from 42,000 lbs with the canadian fuel to empty and 16,000 with the #2. I also went from going with the wind to going against the wind.

I think the #1 problem guys have with "gelling up" is water in the fuel. Almost all the time the guys are blaming the "crap american fuel" that they have to buy down south. I think it's from going from a very humid/warm climate to a very cold dry climate fast. The water condenses out of the air in the tanks, and collects on the inside of the tank. Next time they fill up, trouble is a brewing! Don't you think it's funny how must trucks die shortly after fueling up, even with good Canadian fuel?

[bob h]

quote="allan5oh"]But one thing though... our diesels actually become more efficient when its colder out. Easiest way to tell is how much power it has. It's never going to inject "more" fuel at WOT+full boost. It always injects the same. If it pulls harder in winter, it's creating more horsepower with the same fuel. It becomes more efficient.

...i must look into that =)

cooler air does increase efficiency up to a point... that's why most modern diesels use charge air cooling. but, keep in mind that any pre-'02 engine has plenty of excess air in the combustion chamber

However, you're right when you compare the two one day to the next. I was talking overall, in winter the big difference is the extra friction and air resistance.

I just got back from a trip, I fueled up with #2 in Minnesota. It's -35 with the windchill here. I would never run more then 50% #2 when it's this cold.

you have that option... choosing your fuel blend?

Hell, it even has that 2% biodiesel crap. No problems. Still not much of an improvement in fuel mileage compared to the Canadian fuel I had in there. I think I went from 5.8 to 6.5. But I also went from 42,000 lbs with the canadian fuel to empty and 16,000 with the #2. I also went from going with the wind to going against the wind.

I think the #1 problem guys have with "gelling up" is water in the fuel. Almost all the time the guys are blaming the "crap american fuel" that they have to buy down south. I think it's from going from a very humid/warm climate to a very cold dry climate fast. The water condenses out of the air in the tanks, and collects on the inside of the tank.

that's happening in everyday operation,

i experience that very problem here; it is not the crap fuel, it's because the fuel blend has a lower cloud point. canadian summer fuel will freeze up in the winter as well

Next time they fill up, trouble is a brewing! Don't you think it's funny how must trucks die shortly after fueling up, even with good Canadian fuel?[/quote


water is usually a problem found at the pumps...

RULE #1 - NEVER fuel your truck while the tanker is filling the inground tank!!!

[traveler15301]

I think the #1 problem guys have with "gelling up" is water in the fuel. Almost all the time the guys are blaming the "crap american fuel" that they have to buy down south. I think it's from going from a very humid/warm climate to a very cold dry climate fast. The water condenses out of the air in the tanks, and collects on the inside of the tank.

Nope....water in fuel can be a significant problem...especially if any gets past the fuel/water separator. If liquid water get to the injector...the high pressure and temperature of the injection cycle can rapidly turn that liquid water to steam (albeit on a small level) but the change in volume from liquid to vapour (by a factor of 22.4) can literally blow the tip off an injector!!
Water and any diesel fuel or gasoline are immiscible...means they do not dissolve in each other. The water will separate and since it is more dense, will settle to the bottom of any container. That's why oil spills float on the ocean. bob is right, if you want water in your fuel, fill up while they are filling the underground tank>>>all that fuel getting dumped in will mix that water right into the fuel you pump. We bitch about paying $3/gal for diesel...how 'bout $3/gal for a goodly amount of water!!!

The warm humid air to cold environment can play a part....but that is why you should not let a fuel tank sit empty (or very low)...less air space=less water laden air.
It is also a good idea to drain any water accumulation you may get in your tanks occaisionally...less chance for it to be picked up into the fuel stream AND, there are little microorganisms which lieterally EAT diesel fuel but reside in the water and the fuel/water barrier. Their excrement resembles snotty bogies...and can gum up a filter real quick. So if you get your fuel from a joint that is "infected", if you will, your tanks can now be "infected" as well. There are bio-inhibitors out there that you add (just like anti-gel) to prevent or correct this.

As for "gelling-up" water has nothing whatsoever to do with it.
Diesel is "pure" in the chemical sense (neither is gasoline for that matter). It is a mixture of many long chain hydrocarbons roughly C9-C18 with a mixture flash point of >100F. Non-winterized deisel has a hight proportion of the longer chain molecules and the "gelling" to which you refer is actually the long chain molecules (specifically parrafin wax) separating and partially solidifying into wax. It'll still burn-in a candle...but will clog up a filter or fuel line right quick-like. The additives made to lower the CFPP (cold fuel pour point) or cloud point, if you will, are made to address this. So-called "winterized" fuel is also supposed to fix it...but sometimes does not, especially if the CFPP mix is say for 0F and you go where its -10F...oops.
That's why its a good idea to dump some stuff in with every fill up...especially in winter or if you fill in a warmer clime and then go cold.

[allan5oh]

Yes I know "gelling" up has nothing to do with water, but it seems everyone points to "gelling" up as their problem, meanwhile gelling up has nothing to do with it. It's water, plain and simple.

[BanditsCousin]

As air gets colder, it gets thinner. EFI (fuel injection) compensates with more fuel to offset the lean mixture it normally uses at ambient temperature.

How many of you had cars with carbuerators? You probably remeber having to adjust it based on the season :wink: The EFI does that for us now in cars and trucks, even with altitude changes.

In addition, other factors stated above (like winterblend), longer warm up times (where the truck hasn't gone into "open loop" yet) and many other drag down fuel economy in the winter.

HTH

[allan5oh]

A few things bandit, don't take these the wrong way!

Air gets more dense when it's colder. The molecules are closer together, and the engines make more power and are more efficient. Not "thinner". Maybe you're thinking humidity?

Trucks don't really have an open loop AFAIK. There's no oxygen sensor. It's much much more simple then a car EFI system. There's zero feedback. All it does is look at the rpm, the boost, the pedal position and decides from there. A diesel doesn't care about the air/fuel ratio.

[BanditsCousin]

This is probably true, as I adapted this from my decent automotive knowledge.

I know my turbo truck (GMC Typhoon) loves cold weather!

[bob h]

quote="BanditsCousin"]As air gets colder, it gets thinner.

air density increases as temperature decreases,

air density decreases (thinner) as altitude increases

EFI (fuel injection) compensates with more fuel to offset the lean mixture it normally uses at ambient temperature.

huh?

...are you talking about gasoline fuel injection and fuel trims?

How many of you had cars with carbuerators?

several...

You probably remeber having to adjust it based on the season :wink:

rarely ever...

The EFI does that for us now in cars and trucks, even with altitude changes.

In addition, other factors stated above (like winterblend), longer warm up times (where the truck hasn't gone into "open loop" yet)

fuel injected gassers operate in open loop during engine warm-up. i.e., - STFTs are not adjusted based on O2 signal, because cold O2 sensors are inaccurate. many modern electronic controls use heated O2 sensors to eliminate cold-mode emissions

and many other drag down fuel economy in the winter.

HTH[/quote

[bob h]

quote="allan5oh"]A few things bandit, don't take these the wrong way!

Air gets more dense when it's colder. The molecules are closer together, and the engines make more power and are more efficient. Not "thinner". Maybe you're thinking humidity?

Trucks don't really have an open loop AFAIK. There's no oxygen sensor.

when a control system is in open loop, it simply indicates that a parameter is missing, and the ecm reverts to stored (approximated) info. in a fuel trim loop, the o2 sensor is ignored, and the ecm estimates the fuel/air ratio based on air flow (or pressure), engine speed, engine load, etc.

a HEUI engine can also run in open loop; when the injection pressure sensor signal is lost, the ecm estimates injection rail pressure based on engine speed, fueling pulsewidth, and injection pressure regulator duty cycle

It's much much more simple then a car EFI system.

... used to be ;0)

There's zero feedback.

did you know that an electronic diesel may set an engine code for "lower than expected boost pressure", "injector pulse width too short", or "turbo vane position does not match demand". each of these systems and more use feedback, either in the form of a sensor or calculated parameters

All it does is look at the rpm, the boost, the pedal position and decides from there. A diesel doesn't care about the air/fuel ratio.[/quote

it doesn't care about stoichiometric or lambda, but it does care about the fuel/air ratio... especially post-'02 H/D diesels when the manufacturers all took control of the air delivery to the combustion chamber

[allan5oh]

Yes, but it does not measure the a/f ratio. When I mean feedback, I mean strictly a/f ratio.

You're right, the new engines need to be run very precisely regarding a/f ratios. Too rich and PMs increase, too lean NOx increases. That's why cat uses variable valve timing, and all others use a variable geometry turbo.