big drop in fuel economy

The weather has changed. It is colder, and there is more rain on the roads, both of which hurt mpg.

I should update the mpg chart on my photo page to show this fall & winter's mpg drop. Last year's drop is not representative of weather because the car usage changed also.

 

Yeah welcome to winter LOL. I've also been getting 50 mpg and just put new tires on it at the same time the temp. went way down and now my gas mileage is only 43 mpg. I know its the temp. but still wonder if it would have stayed better with the old tires.

 

Hi CA,

I tend to agree with fuzzy1. Oil change could cause the difference in mileage, if they used the wrong oil, or filled it over the upper mark on the stick, however.

On my 2006 Prius an oil change usually caused a small upward bump in mileage - say 2 or 3 mpg.....

 

The dealer may have reduced your tyre pressure. Mine did.

 

Or the weather: filled my tank today (18F) and got a measley CALCULATED 42+ mpg........temps have been in 20s or less on this tank. OTOH, out there...maybe to much resistance from the water on your roads due to your constant Pacific storms WASHING ashore!!!

Going to be a long time til Spring at this rate...sure a good thing we have alborezz GLOBAL WARMING to $ave us!!! DFO

 

New tires require a break in Period before you'll get back toyour normal mpg. Assuming you bought similar tires.

How Do you know you'll see warmer temps in your area?

Like stated above, check your tire pressure. Unless you request they not, they will adjust your tire pressure. Also keep track of how much rain you have to drive through. Pumping water with your tires wastes a lot of energy.

 

Here is the updated chart:

The 2009 portion was mostly roadtrips while I wasn't working, ending with a sub-45 mpg city tank in an extremely cold December.

The 2010 portion is mostly a fairly consistent commute. The rise and fall follows seasonal temperatures. The 60+ spike is a nicely hypermiled segment of a road trip.

OP's variation is no worse than this, so I would attribute nearly all of it to weather.

 

Are you 100% sure they put 0w20 oil in? The gen 3, 2010 Prius should have that oil (at least here in Europe). If they've put 5w30 in you will get a reduction like you've described. I have posted one or two similar threads about this subject in the past. I even had one incident on my 20k mile service where the mpg's dropped like yours, I informed the dealer and they swore blind that they used 0w20 (and they billed me for this!), however after kicking up a stink the service manager gave me the benefit of the doubt and changed the oil with me there. Sure enough the mpg's returned as did the performance in Power mode. I understand one of the mechanics got severely disciplined. Oh, make sure they haven't over-filled the oil as this too can cause a drop in mpg's. All this make a difference in a normal car too, it's just more obvious in the highly efficient Prius.

Also, as others have said, make sure the dealers haven't reduced the tyre pressures as some seem to think that 30psi is correct - when obviously it isn't. Finally, the lower temperatures will also affect economy.

Hope you get to the bottom of it.

 

I'm down to 37 MPG in Massachusetts, just driving around town. Seems like running the heater and keeping the engine warm in the winter takes more energy than running the AC in the summer. Is that true?

 

If it is robbing heat from the engine and causing the engine to run more often then I would think so.

 

Winter season drops it every time.

 

The Prius gets heat primarily from the engine. For heat to flow, you need a temperature difference. So, the engine has to get hot enough for the heat to flow.

If you are in stop and go driving, the engine does not get hot just by its use for moving the car. So, the automatic control keeps the engine running while your stopped. Because, you are asking it to, by keeping the heater set up high. This is the nature of about half the lost mileage you are experiencing.

I run my heater at 65 F when I need defrosting, and usually do not run it if its above freezing, and I do not need defrosting/defogging. The seats are warm, and in a winter jacket, so am I.

Allot of us will block the grill work with Polyethylene foam tubing - pipe insulation - to get the engine to heat up faster, and hold heat at stop lights longer. This gets the engine to turn off, even with some passenger compartment climate control heating.

There have been copious comments about how to improve on the cold weather mileage on Priuschat the last 2 weeks. Out here in the midwest, the temps went from record warm the end of November, through a period of record cold and/or snow, and now are back to typical. This spawned allot of it. People are freaking out, thinking its December and my mileage is this bad now -what is going to happen in January. Well, nothing much worse - we have been having the January weather early here.....

 

Law of physics. It takes more energy to heat cabin from 20 to 75 than cool from 90 to 75.

 

In Chicago with the change mileage went way down. Killed me to have my nephew warm the car up while loading the car up coming home from Christams at their house. But decided to resist turning car off since wife has been hobbled with broken patella (fell on ice) and didn't want to be accused of being a grinch.... (was nice and toasty warm for the trip home all of 7 miles...