Hi Mike,

That is correct only when assuming that the engine is spending the  
bulk of its running time fully warmed up.

Up here in Canada, that is not the case. Most winter (December - March  
in Toronto) days it takes my vanagon about 5-6 minutes to get the  
needle off the bottom of the gauge. Then, and only then, does the  
mixture normalize.

For someone driving 15-20 minute trips, that means they are spending  
about 25% of the time running rich. That would be sufficient to affect  
their fuel economy.

If you are consistently doing shorter trips, the fuel economy suffers  
big-time.

My personal commute is about 25 miles each way; I know my fuel economy  
is down since the summer time but I figure I also have other  
contributing factors to blame as I haven't replaced any of the  
ignition components or the O2 sensor since I got the van last April.

Happy Trails,

Greg Potts
1987 Wolfsburg Weekender Hardtop
197x Westfakia "Bob the Tomato"
www.busesofthecorn.com
www.pottsfamily.ca

  Quoting Mike Collum <collum@MYFAIRPOINT.NET>:

> Tom Buese wrote:
>> Is that a reason why I get worse gas mileage in the winter?
>
> That shouldn't be much of a factor if the thermostat is working
> correctly, Tom.  Once the engine is warmed up, it doesn't even know it's
> winter.  That's why I use 5W 50 when it's really cold out.  When I first
> start up (cold engine) it thinks the oil is about 5 weight and when it
> gets up to operating temperature, it thinks it's about 50 weight.
>
> Mike