Many clients will call us with concerns about their fuel mileage over the winter months.  More specifically, many will bring their car in complaining of sudden “poor fuel mileage” and ask us to perform testing to find out what the problem is.  But, when testing many of these cars, we often find nothing wrong with them. Instead, what we have generally found is that most people will consume more fuel for several reasons when it gets colder:

1.  Your engine is never fuel efficient until it is completely warmed up.  And, remember, you will pollute more during the warm-up phase too, since the lowest pollution phase isn’t acheived until the engine has reached normal operating temperature.

2. Many people use their remote starter or start their vehicle and let them idle for long periods until the car is warmed up and/or the windows are defrosted.

3. People don’t drive the same distances in the winter as they in summer.  Often it is more shorter trips – grocery store and back, this type of thing.  For those that never drive for more than 15-20 minutes during freezing days, may find that they only drive during this  warm-up cycle, which is not as fuel efficient as when the engine is hot.

4. During winter months, your vehicle will also consume more electrical and horsepower energy in order to run your lights more during dark days, your wipers more during dirty winter days, your heater on full blast (your cars A/C will cycle during any defrost mode with air blowing up on the windshield), and even your rear defroster on more often.  These items consume energy which, in the end, is robbed from the vehicles horsepower demands and therefore more fuel is consumed to run them.

The ANSWER:

The best thing you can do is start your car and drive away as soon as the windows clear (within 30 seconds of starting is the best, if possible).  During this warm-up period, you should drive you car more gently, until the oil reaches its peak performance at full operating temperature.  The reason you should drive away as soon as possible is to reduce the amount of warm-up time required to get the engine hot.  When you step on the gas and go, you are increasing the RPM of the engine and it will warm up faster at these higher RPM’s.  At the same time, the fuel that you may have consumed just sitting in the driveway idling may be enough to carry you to work and back!

And lastly, avoid using your remote starter for any longer than a few minutes before you get outside to clean your windshield.  If you are one of those people that keep re-starting the vehicle after the remote starter has timed out from running too long, you know who I’m talking too 😉  Bottom line is that if you have a remote starter and you never get in your car until it’s warm inside, prepare to stop more often for gas!

On the other hand, there may actually be something wrong with the fuel mileage.  There are many possiblities, but the most common culprits are degraded or failed oxygen sensors and weak thermostats.  The oxygen sensor(s) is one of the main sensors responsible for controlling fuel consumption.  The thermostat is the one part that controls the engine temperature.  If it is weak, it may not allow the engine to get to operating temperature on a cold day, keeping the engine running during the poor fuel economy phase of the warm-up cycle.

Phil