Newsgroups: rec.autos.misc
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From: b3d74c12@users.realize.com
Subject: Re: lower miles per gallon, why?
Message-ID: <1a7cf$02ab.1f@neontetra.realize.com>
Date: Sun, 10 Jan 1999 08:42:11 GMT
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Xref: news.jprc.com rec.autos.misc:28630

On 1/5/99, Chris Watkins <umytbnxt@mindspring.com> wrote:
> duliaa@usa.net wrote:
> > 
> > I have a '96 Metro, and I've been pretty happy with it
> > until now.  I've always gotten 48 MPG on the highway
> > doing about 75-80 mph.  But on my last few highway trips
> > I only get 42 mpg.
> > 
> > I took the car in to the dealer and they couldn't figure
> > out what's wrong with it.  The only answer I got from the
> > mechanic was "its winter".  Heck, last winter I was
> > getting 48 mpg.  ANyway, I'm hoping you may be able to
> > give me some suggestions.
> > 
> > More info: I accidentally drove the car at 90 mph for
> > an hour or so on the highway (its max speed on the meter)
> > while following the traffic.  Could this break anything?
> > I'd figure if GM prints 90 mph, then I can drive it.
> > 
> > Please post replies since the email address is not
> > correct to prevent spam.
> > 
> > -thanks
> 
> You didn't say how many miles were on the vehicle, or if this was a very 
> sudden occurence, or something gradual over a period of time. You 
mentioned
> "the last few road trips", but how long had it been since you had 
actually
> checked the mileage ?  Mileage normally degrades somewhat, over the life 
of
> the vehicle.
> 
> There are so many things which could cause it that I will only list the
> first few which pop into my head...
> 
> Thermostat... If opening earlier, or stuck open, will not hold the 
coolant
> at a high enough temperature. A major part of the engine's fuel 
calculations
> is from the engine coolant temp sensor. If you are only getting say, 180
> degrees F  instead of the normal 195 - 205 or so, then you'll be getting
> worse fuel mileage.
> 
> Coolant temp sensor itself (same reasons as above)
> 
> Lazy Oxygen sensor... Not completely dead, so as to turn on the 
MIL/CEL/SES
> (whichever;) Light, but just updating slowly enough to cause poor 
mileage.
> (note... extended full throttle driving could possibly damage the O2,
> as the mixture at WOT is a wee bit rich by design) 
> You'd normally notice a bit of "surge" with this one.
> 
> Cat Convereter stopping up.  Maybe not bad enough to notice decreased
> performance, but possibly just enough to have created more backpressure,
> and therefore, lower fuel mileage at higher speeds.  (another item which
> *might* be damaged from extensive Wide Open Throttle operation)
> 
> tire pressure.  6mpg ?  uh-huh.  Cold weather, check those tires.
> 
> changed to wider tires... (more drag... same as running lower PSI above)
> 
> Changed to a higher viscosity oil (ie 20W50 or straight 40-50W)
> 
> Changed gas brands (or octane)
> 
> Dirty air filter  (obvious)
> 
> spark plugs  (some cars go 110,000, some need them at 40,000... driving
> habits can influence this somewhat.  My ole Ventura needs 'em every 
6,000 , 
> but then again, it's a 375hp duel-pumpin, gas-guzzlin POS on the street 
;)
> 
> The list goes on, but these are among the most likely.
> 
> You didn't mention if the vehicle had recently had any other problems, 
like...
> 
> hard starting
> recently overheated
> beginning to use oil
> Addition of two 500 watt amps with 18 inch subwoofers, etc... 
> HUGE draw on the alternator, and guaranteed to lessen fuel mileage some.
> 
> And it could just be that you're not driving exactly the same... for 
whatever
> reason. 6 MPG sounds like a lot to someone who checks their mileage 
> regularly, but it can be a bit difficult to track down without a lot of
> info and time, sometimes.  
> 
> 
> 
> 
> 
> -- 
> Chris Watkins
> C_Watkins on TEN's Nascar Racing Online Series  
> Dirty Hobby Motorsports, Douglasville, Ga.
> Moderator, rec.autos.sport.nascar.moderated


Chris,
I know some states, such as Colorado for example add more ethonol in the 
gasoline in the winter.  My miles per gallon have also gone down a bit, 
but I warm my car up longer in the winter months


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