jeff@adelie.UUCP (Jeff Moskow) (01/17/86)
I have noticed that my gas mileage drops by 15-20% every winter (I own a
1982 Honda Accord). I have always attributed this to the colder temperature,
but I still don't understand exactly why it should have such a drastic effect
on my mileage. If anyone can explain why this happens (and if there is any
way to avoid it) I'd like to know.
--
LIVE: Jeff Moskow, (617) 965-8480 x15
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ARPA: adelie!jeff@harvard.ARPAtoma@tekchips.UUCP (Tom Almy) (01/20/86)
In article <576@adelie.UUCP> jeff@adelie.UUCP (Jeff Moskow) writes: >I have noticed that my gas mileage drops by 15-20% every winter (I own a >1982 Honda Accord). I have always attributed this to the colder temperature, >but I still don't understand exactly why it should have such a drastic effect >on my mileage. If anyone can explain why this happens (and if there is any >way to avoid it) I'd like to know. > Some ideas: 1. Engine spends more time "cold", with a richer fuel mixture. 2. Greater use of electrical accessories (heater fan, lights). Tom Almy
throopw@dg_rtp.UUCP (01/22/86)
> I have noticed that my gas mileage drops by 15-20% every winter I think the effect has two major components, and I'm not sure which is greater. First, the thermal component. The car is breathing colder air in the winter, and this heat must come from somewhere. In this case, in order to get cold air to expand the "same ammount" as hot air (and hence provide the same amount of power) more gas must be burned. Second, the humidity component. Winter air is *much* less humid than summer air. A little water in the air works wonders for power output. In fact, some aircraft engines used to be water injected, and there are (mostly useless, but not totally bogus) gadgets that humidify intake air on a standard carburated engine. As to what you can do about it, you can make sure that your input air is preheated as far as is possible (most cars nowadays route the intake past heated engine surfaces). You might want to look into humidification gadgets, but this is *far* *far* more likely to be a rip-off in one form or another. And oh, yes, if you have snow and ice sitting on your car, the wind resistance goes way way up, so scrape it every morning. > Jeff Moskow {harvard | decvax!cca!emacs}!adelie!jeff -- Wayne Throop at Data General, RTP, NC <the-known-world>!mcnc!rti-sel!dg_rtp!throopw
gvcormack@watmum.UUCP (Gordon V. Cormack) (01/23/86)
> > I have noticed that my gas mileage drops by 15-20% every winter > > I think the effect has two major components, and I'm not sure which is > greater. First, the thermal component. The car is breathing colder air > in the winter, and this heat must come from somewhere. In this case, in > order to get cold air to expand the "same ammount" as hot air (and hence > provide the same amount of power) more gas must be burned. > > Second, the humidity component. Winter air is *much* less humid than > summer air. A little water in the air works wonders for power output. > > And oh, yes, if you have snow and ice sitting on your car, the wind > resistance goes way way up, so scrape it every morning. > > > Jeff Moskow {harvard | decvax!cca!emacs}!adelie!jeff I didn't notice a "-)" on this posting, so I am taking it seriously. The second point (about humidity) is absolutely false, and the first and third points (heating cold air and wind resistance of snow) are absolutely insignificant. Since I haven't seen a succinct posting of the factors involved in poor gas mileage, I will enumerate what I think are the most important ones: (1) Until the engine is completely warm it must run with the mixture enriched (choke on) in order to get enough vaporized gas to the cylinder to burn. This extra gas is wasted. (2) The tires, bearings, and transmission are stiffer in cold weather. However, this effect is much less significant than (1). (3) Many people let their cars warm up in cold weather, wasting gas. Also, many people take more short trips in cold weather. I have driven on many long highway trips in winter, and have noticed no significant difference between winter and summer highway gas mileage. This observation illustrates that cold weather affects mainly the warm-up performance of the engine, not the steady-state performance.
ksbszabo@watvlsi.UUCP (Kevin Szabo) (01/23/86)
>> I have noticed that my gas mileage drops by 15-20% every winter > >if you have snow and ice sitting on your car, the wind >resistance goes way way up, so scrape it every morning. The wind resistance also goes up due to the increse in the density of cold air. This can be a major factor. Kevin -- Kevin Szabo' ihnp4!watmath!watvlsi!ksbszabo (VLSI Group,U of Waterloo,Ont,Can)
midkiff@uiucdcsb.CS.UIUC.EDU (01/23/86)
Is it possible that reduced traction because of wet/snowy roads could cause part of it?
marauder@fluke.UUCP (Bill Landsborough) (01/24/86)
In article <103@dg_rtp.UUCP> throopw@dg_rtp.UUCP writes: >> I have noticed that my gas mileage drops by 15-20% every winter > > >As to what you can do about it, you can make sure that your input air is >preheated as far as is possible (most cars nowadays route the intake >past heated engine surfaces). > >Wayne Throop at Data General, RTP, NC Actually the engine will run better with cold air than warm air. The air goes from contraction to expansion and the further extreme of contraction (ie. cold) the better. That is why serious racers of all combustion engine of all type keep there fuels cold and the air intake out in the open. The temporary air intakes are run down to the exhaust manifold to warm the engine quickly but once the engine is warm it is suppose to switch to cold, unrestricted air. Like you did mention, humid air makes things even better. Bill Landsborough ---- "Love is patient and kind; love is not jealous or boastful; it is not arrogant or rude... Love bears all things, believes all things, hopes all things, endures all things." 1 Corinthians 13:4-7
ljo@drutx.UUCP (OchsL) (01/25/86)
> (2) The tires, bearings, and transmission are stiffer in cold > weather. However, this effect is much less significant than > (1). I believe that stiffer tires would cause less rolling resistance and thus contribute to increased gas mileage. With a typical boring engineer response, Larry O. AT&T Info. Systems, Denver, CO.
droms@purdue.UUCP (Ralph E. Droms) (01/25/86)
Well, I once knew a Nuclear Engineering PhD who was *convinced* a car's reduced gas mileage in the winter was due to all the energy being wasted through the heater. I understand she has a job in Harrisburg, PA now... - Ralph -- ================================================================== Ralph Droms ihnp4!purdue!droms CS G73 droms@purdue.edu Dept. of Computer Sciences droms@purdue.csnet Purdue University West Lafayette, IN 47907
smh@mhuxl.UUCP (henning) (01/25/86)
> I believe that stiffer tires would cause less rolling resistance > and thus contribute to increased gas mileage. You would be right if the tires were round on the bottom, but they are not and it takes more energy in the winter to make the bottom flat in a defferent place as the tire rolls. However, when it is really cold, the flat spot stays in one place and you do waste less energy turnng the tire, but then you loose it in the tar that used to be oil and from the fact that the engine never gets up to an efficient temperature.
throopw@dg_rtp.UUCP (01/27/86)
> > > I have noticed that my gas mileage drops by 15-20% every winter > > > > [insert foot in mouth, give wrong "answer"] > I didn't notice a "-)" on this posting, so I am taking it seriously. Uh.... thanks. I think. :-) > The second point (about humidity) is absolutely false, and the > first and third points (heating cold air and wind resistance of > snow) are absolutely insignificant. Since you are right, and I'm wrong, I'm reduced to picking nits. So here goes. While you are correct that the relative humidity is not particularly lower in winter than in summer, the absolute humidity *is* significantly lower. This *can* have an effect on the power output of the engine, but it is (I am now fairly sure) quite minor. Wind resistance now... there I think you are slightly wrong about the importance of the effect. I agree that the effect is *relatively* minor, but wind losses go up rapidly with speed, and if most of the travel time is spent at 55 or higher, this can amount to a couple of percent difference. Nothing like the >15% in the problem, but certainly not absolutely insignificant. In any event, the *major* effects are more likely increased per-trip overhead (choke "wastage", warming up too long, stiff power train until warmup, etc). The best bet for "solving" the problem is to make sure the car is tuned properly, make sure the choke isn't partially stuck in cold weather, and don't waste gas by warming up the car before getting on the road. But then, I'm known to give bogus answers, so why should you listen to me? And, of course, I apologize for jumping in with a misleading and incorrect response. -- (Basil Fawlty, rehearsing to himself while going to apologize to a guest:) "I'm sorry, I made a terrible mistake... I'm sorry, I made a terrible mistake... I'm sorry, I made a terrible mistake..." (finally reaching the guest's room, he strikes a pose, and says:) "I'm sorry, my wife has made a terrible mistake!" -- "Pay no attention to that man behing the curtain!" -- Wayne Throop at Data General, RTP, NC <the-known-world>!mcnc!rti-sel!dg_rtp!throopw
halb@tekig5.UUCP (Hal Bates) (01/27/86)
In article <372@watmum.UUCP> gvcormack@watmum.UUCP (Gordon V. Cormack) writes: >> > I have noticed that my gas mileage drops by 15-20% every winter >> >> I think the effect has two major components, and I'm not sure which is >> greater. First, the thermal component. The car is breathing colder air >> in the winter, and this heat must come from somewhere. In this case, in >> order to get cold air to expand the "same ammount" as hot air (and hence >> provide the same amount of power) more gas must be burned. >> >> Second, the humidity component. Winter air is *much* less humid than >> summer air. A little water in the air works wonders for power output. >> >> And oh, yes, if you have snow and ice sitting on your car, the wind >> resistance goes way way up, so scrape it every morning. >> >> > Jeff Moskow {harvard | decvax!cca!emacs}!adelie!jeff > >I didn't notice a "-)" on this posting, so I am taking it seriously. I didnt notice a "-)" on this posting, so I am taking it seriously. >The second point (about humidity) is absolutely false, and the >first and third points (heating cold air and wind resistance of >snow) are absolutely insignificant. I didnt know any thing is absolutely insignificant. I am glad, however, the auto industry didnt say that about aerodynamics. I will say that I wouldnt spend time freezing my ass to remove snow from my car to save a few cents worth of fuel on a cold winter morn. The second point about humidity is true. Some parts of the country have high humidity in winter (west coast) others have low humidity. Higher humidity will hold off combustion allowing for lower octane requirements or larger spark advance on the distributer. Both make for better fuel economy. The internal combustion engine will perform the best with a large amount of moisture present. One way to duplicate that high RH environment is to install a water injection system to your engine. Inexpensive, and the results are dramatic. >Since I haven't seen a succinct posting of the factors involved in >poor gas mileage, I will enumerate what I think are the most important >ones: enumerate? no shit; I didnt know that people enumerated in net.auto.tech. -) > > (1) Until the engine is completely warm it must run with the > mixture enriched (choke on) in order to get enough vaporized > gas to the cylinder to burn. This extra gas is wasted. Why then, is it necessaty to richen the fuel mixture? It seems the second article states that. Why argue a point you both seem to agree on? Automatic chokes waste fuel. They are improving the design, and with u'p controlled injectors the choke control is excellent, but the spring controlled stuff is a real money eater. Gimmee a knob with CHOKE on the label. > > (2) The tires, bearings, and transmission are stiffer in cold > weather. However, this effect is much less significant than > (1). > This is true to some degree. Horespower is wasted in warming up the 90W and bearing grease. This may take several miles to accomplish = loss of fuel economy. > (3) Many people let their cars warm up in cold weather, wasting > gas. Also, many people take more short trips in cold > weather. It it true that warmup wastes fuel. So dont warm up for more that 30 seconds unless the temp is very cold. All that is necessary for the engine to operate is to get the oil up to pressure before moving out. Take it eaisy until warmup occurres. It is better for a engine NOT to sit at idle soaking up that rich gas past the rings and into the oil (diluting it), fouling the plugs, and adding carbon deposits to the combustion chamber. For the sake of argument, cold weather fuel economy has nothing to do with short or long trips, if the operator does his or her part. People still commute to work even in winter. But items like choke and warmup require a thought process from the driver. The luxurey of getting into a warm car means hardship on the engine and the waste of fuel may override the ill effects on the engine will suffer in order to supply that warmth. A few years back I knew a guy who would start his engine (early in the morn) gun it up to 3 or 4000 RPM and let it idle there for 20 minutes. Then he was pissed when the engine started to use oil. Screamed - this car is a lemon. oh-well >I have driven on many long highway trips in winter, and have noticed >no significant difference between winter and summer highway gas >mileage. This observation illustrates that cold weather affects >mainly the warm-up performance of the engine, not the steady-state >performance. Temp and humidity will effect all engines. Cooler (not freezing) air and higher humidity will improve performance and warm dry air will be a detrement. tektrinix!tekig5!halb
neal@weitek.UUCP (Neal Bedard) (01/28/86)
In article <372@watmum.UUCP>, gvcormack@watmum.UUCP (Gordon V. Cormack) writes: > > (1) Until the engine is completely warm it must run with the > mixture enriched (choke on) in order to get enough vaporized > gas to the cylinder to burn. This extra gas is wasted. > > (2) The tires, bearings, and transmission are stiffer in cold > weather. However, this effect is much less significant than > (1). > > (3) Many people let their cars warm up in cold weather, wasting > gas. Also, many people take more short trips in cold > weather. Three more: (4) In snow: wheelspin decreases mileage (the original question was from MA, no?) (5) In rain: additional rolling resistance due to water being pushed aside by the tires decreases mileage (applies to fresh snow as well.) (6) In any foul weather: spending more time driving in lower gears (since safe speeds are reduced) decreases mileage. Also, spending more time coping with dense traffic has a like effect (alludes to (3) above.) The higher air density/ water content arguments are insignificant (in any event, both would *increase* mileage) unless one is discussing the effects of turbochargers with and without intercooling and/or water injection. [Anyone remember that snake-oil ad for the `water injector' that J.C. Whitney used to sell? They used to say "Ever notice how much better your car runs in a dense fog... etc.?"] The crux of the biscuit is that wintertime driving habits (including engine warm-up) are the only significant reasons for lower winter mileage. Notice that some people seem not to encounter this. I suspect that members of this group live in places where the winters aren't so severe. -Neal -- "If I owned half of that dog, I'd shoot my half." -Pudd'nhead Wilson UUCP: {turtlevax, resonex, cae780}!weitek!neal
daw1@mhuxl.UUCP (Douglas A. Williams) (01/29/86)
> Well, I once knew a Nuclear Engineering PhD who was *convinced* > a car's reduced gas mileage in the winter was due to all the > energy being wasted through the heater. > > I understand she has a job in Harrisburg, PA now... > > - Ralph Oh shit! - Doug Reading, PA
jacobson@fluke.UUCP (David Jacobson) (01/30/86)
I agree that probably the most significant thing is warm up time and choke closed time being longer in the winter. But here is another factor that no one has mentioned yet: During the winter more electrical load is placed on the car. For one, many rush hour type commutes are after dark and hence the lights are on. For another, the heater is on, and although the heat is free once the engine is warmed up, the electricity to run the fan isn't. Finally, during the winter one is more likely to operate the windshield wipers and the energy intensive rear window defogger. At idle, turning on my rear window defogger causes a very noticible slow down in the engine speed as the alternator buckles down to providing the electricity. -- David Jacobson ... ihnp4!uw-beaver!fluke!jacobson
smh@mhuxl.UUCP (henning) (01/30/86)
**** **** From the keys of Steve Henning, AT&T Bell Labs, Reading, PA mhuxl!smh > (1) Until the engine is completely warm it must run with the > mixture enriched (choke on) in order to get enough vaporized > gas to the cylinder to burn. This extra gas is wasted. When the air is cold, there are more oxygen molecules per cubic foot, necessitating the use of more gasoline per cubic foot of air. Thus the need of enrichment of the mixture. After the engine warms up, all of this extra gas is converted into useable energy, but much of it is diverted to heating and powering things which do not need heating or powering in warmer weather, hence the loss. Also the warm up time is very costly.
ray@othervax.UUCP (Raymond D. Dunn) (02/05/86)
In article <372@watmum.UUCP> gvcormack@watmum.UUCP (Gordon V. Cormack) responds to a previous article: >> > I have noticed that my gas mileage drops by 15-20% every winter >> >> I think the effect has two major components, and I'm not sure which is >> greater. First, the thermal component. The car is breathing colder air >> in the winter, and this heat must come from somewhere. In this case, in >> order to get cold air to expand the "same ammount" as hot air (and hence >> provide the same amount of power) more gas must be burned. >> >> Second, the humidity component. Winter air is *much* less humid than >> summer air. A little water in the air works wonders for power output. >> >> And oh, yes, if you have snow and ice sitting on your car, the wind >> resistance goes way way up, so scrape it every morning. >> >I didn't notice a "-)" on this posting, so I am taking it seriously. >The second point (about humidity) is absolutely false, and the >first and third points (heating cold air and wind resistance of >snow) are absolutely insignificant. > I wish that when people made definitive statements, they would give their reasons/sources. Just because you pontificate "absolutely false", and "absolutely insignificant" gives your opinion no more weight than the original. As I understand it, and have read in several places, high humidity *does* have a significant affect on the airflow into the carb & cylinders, and wind resistance of sevaral inches of snow *does* have a significant affect on gas consumption - consider that (as reported not-so-recently in Consumer Reports - that fount of information (:-)) driving with your window wound down can affect consumption by 2 or 3mpg. Any *informed* person like to comment (with checkable info rather than opinions)? Ray Dunn. ..philabs!micomvax!othervax!ray
jeq@laidbak.UUCP (Jonathan E. Quist) (02/10/86)
re: comments on air temperature and humidity vs. fuel economy Cold air is more dense than warm air, so a proper fuel/air mixture requires more fuel per unit volume of air. Humid air is less dense than dry air, so it would seem reasonable that humid air would require less fuel per unit volume of air for the proper mixture. In aircraft operating at high altitudes ( in this case, greater than about 5000 feet above sea level) the fuel/air mixture is leaned to increase fuel economy. (In the case of a non-supercharged piston engined aircraft, the decrease in fuel burn rate can be greater than 25%, if memory serves me correctly.) I realize I'm over-simplifying things quite a bit, and I'm probably ignoring several factors, but my point is that air temperature and humidity will affect fuel economy. Jonathan E. Quist ihnp4!laidbak!jeq