[V8] Cold killing gas mileage

Tue Jan 4 16:36:36 EST 2005

You are quite correct Paul that the thermostat keeps the engine at the right
temp. In cold weather though, the the radiator gets way too efficient. The
incomming water (to the motor) has to be warmed back up to 90C by burning
gasoline. If you keep the radiator warm by blocking cold air flow over it, you
do not have to spend the extra gas to "keep the radiator warm".
In extreem cold the radiator can freeze up solid while you are driving -
ironically causing a boil over.
This is why you always see radiator covers on big trucks. The motor can not keep
itself warm enough to run efficiently.
One winter trip through Wyoming is all it takes to drive this point home.

If you have a good temp guage you can actually see when the thermostat opens in
these conditions. The guage will go up around a normal temp, then the thermostat
will open and a deluge of freezing cold water rushes into the motor. By the time
the slow acting thermostat shuts off, the the engine has been cooled too much,
then the cycle repeats itself. It is quite possible that you cool the motor so
much that it goes back into open loop warm-up mode - sort of like driving with
the choke on.

Dave

Quoting pjager at telus.net:

> A cold drivetrain:
>
> Needs more fuel
> Oil is more viscous
> Drivetain fluids are more viscous
>
>
> To boost economy consider:
>
> Installation of engine warmer
> Use a 5W 15 / 20 Oil
> Get the tire pressure to max to reduce rolling resistance
> Make sure the brakes aren't dragging and the pins are lubed up.
> Shift to Neutral to coast when possible.
> Remove unecessary items from the trunk.
>
> The thermostat controls engine temperature, not the rad temp. My old 5000
> the t-stat failed OPEN so the engine stayed too cool.
>
> Paul Jager
> www.jageng.com
>
> PS I've got a Audi BOSE Cassette head unit with code and manual for sale
> from my '93V8Q.
> pjager at jageng.com
>
>
>
>
>
> -----Original Message-----
> From: v8-bounces at audifans.com [mailto:v8-bounces at audifans.com]On Behalf
> Of dsaad at icehouse.net
> Sent: January 3, 2005 8:18 AM
> To: v8 at audifans.com
> Subject: Re: [V8] Cold killing gas mileage
>
>
> If the air temp is going to stay in the low twenties for a while, block off
> most
> of the radiator with cardboard or something. The reduction in mileage has a
> lot
> to do with the thermostat trying to keep the radiator at 90C.
> This is exactly why you see radiator covers on all the diesel big rigs.
> Just be sure to watch the temp guage closely.
>
> Dave
>
>
> Quoting Michael Larosa Jr <Mc.Larosa at Sun.COM>:
>
> >
> >
> > Every winter I lost 2-3mpg as well,  I attributed to the reformulation of
> > gas that tbey do in the winter here in NH.....
> >
> > Mike,
> >
> >
> >
> > QuickAudi at aol.com wrote:
> > > Well, I'm kinda stumped.  At 60 degrees, I can get well into the low 20s
> > for gas mileage, up to 23.  When it is 20 degrees, like lately, up to
> about
> > 45 or so, my gas mileage barely pushes 18-19.  What gives?  The air temp
> > sensor "looks" ok, MAF is original, and OXS (3 wire) was replaced earlier
> in
> > the year.  Those were my three guesses.  Also have replaced G82/83 temp
> > sensors and the one on the back of the passenger side cylinder head.
> > > Oh yeah: MERRY CHRISTMAS!!!
> > >
> > > Joel
> > > '90 V8q
> > > '86 5kcstq
> > > _______________________________________________
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> > --
> >
> >      _/_/_/  _/    _/  _/     _/      Mike LaRosa
> >     _/      _/    _/  _/_/   _/       TSE - HAS
> >    _/_/_/  _/    _/  _/  _/ _/        1617 Southwood Drive
> >       _/  _/    _/  _/   _/_/         Nashua, NH 03063
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> >    S U N                              Phone: 781/442-1250
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