I know gas mileage goes down in the winter but come on...

[jimdigs]

....I use "Fuelly" to keep track of my mpg. I've gone from 40, 39 mpg in Aug. through Oct. and this last fill up I got 35!! What the heck? Before that was 36, before that was 37. So a steady slow descent.

[fastivaca]

"Winter" gas?

[ryanprins13]

Loosing 10% on your gas milage is normal for most vehicles weather its a van, truck or small car. Oil, grease and coolant is colder on startup so there are high pumping draws, they take longer to heat up- especially oil. You use your headlights and heater more and there is more rolling resistance from winter tires, snow/slush/water. People also tend to let their vehicles idle to warm up.


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[bolokid]

I went to Seattle yesterday, temperature 21 to 35. Gas mileage usually 38-40 mpg with the 5 speed, I got 31, 33 and 36. I assumed it's the cold weather.

[TorqueEffect]

Yeah, my fillup today I only netted 34 MPG. That's with a vacuum leak somewhere too.

[TominMO]

Also, cold air is denser, so at hwy speeds it will create more drag than in the summer. Atmospheric drag is negligible below ~45-50 MPH.

[jimdigs]

Ok, I knew it went down but I didn't think it was as far as mine had gone but it appears about right with what others are getting.

[AlaskaFestivaGuy]

Won't cold air, being denser, require more fuel per unit volume of air to obtain a suitable mixture?

Also, dry air is denser. The past four days in Seattle have been cold and very dry, with rare clear blue skies and visibility in excess of 100 miles at ground level.

[BeeDuhb]

Also in Seattle area for reference, just got 36 mpg on las fill up.


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[Advancedynamix]

Another thing to note is that the engine management richens the mixture while the engine is below operating temperature, and the oxygen sensor is not used to fine tune the fuel mixture. Festivas have a tendency to run cold, especially in cold weather.
One trick to help with this is to switch to a dual element thermostat for a 1.6 miata. These thermostats work better for a quicker warm up and a more precise control on engine temperature. They are a bit on the expensive side though.

[TominMO]

Another thing to note is that the engine management riches the mixture while the engine is under operating temperature, and the oxygen sensor is not used to fine tune the fuel mixture. Festivas have a tendency to run cold, especially in cold weather.
One trick to help with this is to switch to a dual element thermostat for a 1.6 miata. These thermostats work better for a quicker warm up and a more precise control on engine temperature. They are a bit on the expensive side though.

They are a little expensive as you say, but the fuel savings will more than make up for it. Guess I'm finally gonna have to get one, not so much for gas mileage tho as for better heat. I'm finally coming around to wanting to try the dual-stage t-stat to see if it really matters.

[1990new]

Here is a link to an article that explains most of the reasons for lower gas mileage during colder weather.
http://wxbrad.com/why-cold-weather-g...r-gas-mileage/

[dhnorris]

34 last fill up, winter gas sucks and I think Festiva radiators are sized for a 5.9 cummins. To get heat I block radiator and unplug fan otherwise mileage drops even further

[BeeDuhb]

Is unplugging the fan a good idea?


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[bolokid]

OK, it's warming up here in Eastern Washington, temperatures been 30-40. I filled up today, 36.5 mpg. Gas mileage appears to be improving with warmer temperatures.