So, I have a 2003 V70 AWD (not the Cross Country) with a 2.5T motor. 118K miles on it.

95% of my driving consists of 6 miles each way to and from the train station on two lane back roads. I do about 35-40 mph and there is only one stop light.

Historically, my mileage was in the 22 mpg range per the computer. However, this winter it quickly plummeted down to the low 19's. Then, sure enough two weeks ago (mid April) it has started climbing back up again.

There are only two things I can think of:
1. we had a brutally cold winter in CT this year. I think from Jan 1 to mid March the temp was rarely above 20 degrees. Would the car have enrichened the fuel mix during the colder weather?
2. Mid April I dumped a bottle of Techron in the gas tank - as is my practice every 6 months. Could that have cleaned something out of the fuel system.

Just curious your thoughts

Bob

 

A few possibilities...

The gas companies are mandated to mess with their ethanol / additive formulas between summer and winter in most areas. Ethanol doesn't contain nearly the energy that gasoline does, so when the mix goes more toward ethanol, your mileage will go down. That, and the fact that it takes a gallon or so of real gas to produce a gallon of ethanol makes that one of the dumber things to come out of Washington DC (and that's saying something).

Also, you're right that cold weather will mean that it takes your engine longer to warm up enough to turn off the enrichment function, so you're running richer more of the time during the winter.

The effective air pressure in your tires will decrease in the cold, increasing rolling resistance. Also, the aerodynamic (wind) resistance goes up with denser, cooler air.

Or maybe you just drive faster when it's cold...

 

Wow, I forgot about the gas formulations changing with the season. They absolutely do that here in the NE. And tire pressures dropping in the cold too... But, I definitely drive slower when it's cold, at least the first 10-15 mins until the engine warms - which is basically my entire drive to the train station.

Thanks

Bob

 

Given the very cold weather and the short distance, the engine might not have enough time to properly warm up, so gas mileage will suffer.

But to be sure, check the thermostat closes properly as this is a typical part to go bad on a 10 years old Volvo. Start the engine from cold and let it idle for a minute or two. Then put a hand on the upper thick radiator hose. If it's slightly warm, then the thermostat doesn't fully close any long, and affects the mpg.