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Posting-Version: version B 2.10.2 9/18/84; site watmum.UUCP
Path: utzoo!watmath!watnot!watmum!gvcormack
From: gvcormack@watmum.UUCP (Gordon V. Cormack)
Newsgroups: net.auto.tech
Subject: Re: Gas Mileage
Message-ID: <372@watmum.UUCP>
Date: Thu, 23-Jan-86 09:22:22 EST
Article-I.D.: watmum.372
Posted: Thu Jan 23 09:22:22 1986
Date-Received: Fri, 24-Jan-86 08:36:53 EST
References: <576@adelie.UUCP> <103@dg_rtp.UUCP>
Organization: U of Waterloo, Ontario
Lines: 42

> > 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.