Suddenly poor gas mileage

Your Prius is extremely sensitive to cold weather and short trips more so than any other car in the world.

In our Prius if I take short trips in cold wet rainy weather, trips length about 5 miles, temps in the 40's F , with water on the roadway, lights, windshield wipers on, heater and defroster, I will get about 35 MPG's.

Summer with temps in the 65-75 F range, dry roads, MPG's are now in the 50's MPG.

Long trips in warm dry weather 60 mpg is easily obtained with
conservative driving habits.

alfon

 

I seem to get much better mileage on the highway than in the city. Are you just driving in the city now? Is it hilly? I have experienced a similar drop in mileage (mid-50's to mid-40's) but I chalk this up to cold weather. Running the windshield wipers, heater, heated seat!, ,, tire slippage to some extent, driving more in the dark, etc all seem to add up. The hit for just running the A/C isn't so bad, but probably worse in MD than in MA. Even with a 400 foot elevation change from home to work, I do much better in the warmer months.

I always use the recommended grade of synthetic and change about every 4,000 miles, so I couldn't help on this issue.

Do you find you are running the accessories more now? I got my car about the same time as you, so if it were something like tire wear, we would probably have similar issues. Mine are still good.

 

Why does mileage drop in winter? — Autoblog Green
Cold Weather Vehicle Fuel Mileage – Why Winter Fuel Economy Drops – Fuel Mileage Drop in Vehicles
Car Talk
Why does gas mileage drop in winter? | StarTribune.com

Check your tire pressures and inflate to (or near) sidewall max. Your short trips are killing your mileage, besides the cold weather.

With your weather being so cold (I see a forecast of 26 F high, 7 F low for tomorrow), you should definitely block your grille and also consider better heater usage. By better, I mean don't use auto and set the heat to but fan to off when stopped or driving at low speeds. This prevents the ICE from running to provide cabin heat, further hurting your mileage.

You can also consider an engine block heater, but that's a lot more $ than blocking the grille.

I'm not sure I understand what you're asking by "why I am getting such bad mileage in the city and get better mileage on the high way." Please clarify.

 

It's the weather and shorter trips. I take short drives in winter (Midwest) and my average winter month MPG is in the 30s. In summer, it is mid-50s.

 

That is the problem. Nothing you can do about it except combine trips and preheat the engine block with a heater. You would be a prime candidate for a PriusEV.

 

Take a drive like your old commute on a warm dry-road day and see if mpg still same as before.

 

If you can stand it, not using the cabin heat (that is, turn OFF the fan in the Climate display) will help also. Be comforted in the knowledge that every car does even worse than a Prius under these conditions.

 

The average ambient temperature is not the main culprit. It is the simple fact that you engine does not heat up to proper operating temperature before your trip is over. The Prius can only average approx 35mpg when the engine is cold. Once warmed up it can now maximize efficiency and get 50+. So if your commute consists of you driving in warm-up mode only then you will never see better than 30-40mpg.

The colder the ambient temperature, the longer it takes to complete the warm up cycle. I think this will have a marginal effect on overall fuel efficiency though because even on a 70deg morning you will be unlikely to reach operating temperature and stage4 operation within 5 miles of driving. Even if you did reach operating temperature you have still spent the majority of your time in open loop warm up mode.

 

When the 2010's were released the manual said that synthetic oil was recommended every 5000 miles, but if none was available you could use regular oil once to make it to the next oil change of synthetic.

Later, Toyota extended the oil change interval to 10,000 miles, but only if you use synthetic. Do not try to stretch the regular oil past 5000. Toyota did an extremely poor job of making this announcement, so we have huge threads arguing about it.

http://priuschat.com/forums/gen-iii...ally-revised-10000-miles-1-year-verified.html

 

Not so.

My 2003 Jetta TDI wagon with a 5 speed manual still gets 50 MPG
even in the current winter conditions. Our Prius gets better MPG's in the summer than the Jetta, but in the winter the Prius dives into the mid 40's to sometimes the low 40's mpgs.

The Jetta is more consistent in MPG. I base this on fact,
the Jetta has 133,000 miles and the Prius 44,000 miles.

al

 

And what is the average combined city/hwy MPG for both cars in winter and summer? Please include % of hwy miles driven.

 

I'm confused by the above since the last paragraphs are text from me.

You might find Most fuel-efficient cars and the links at http://priuschat.com/forums/other-c...s-best-worst-lists-april-2010-auto-issue.html interesting.

It sounds like your city mileage expectations are based on EPA city numbers. If so, please read http://priuschat.com/forums/other-c...uth-about-epa-city-highway-mpg-estimates.html.

 

It really sucks your dealership and the manual gave you the wrong info on the type of oil to use in your car.

What kind of oil is in the engine right now? Do you have a sticker on your windshield saying the brand/type and also how many miles you happen to have been running the engine with that oil?

 

Never had a car(s) so susceptible to variable gas mileage.

We have had a 2002, 2004, 2008, and just got a 2010. They all do pretty much the same thing. Get 40-46 plus in summer in town, (45 on hwy at 70 mph)
......and the in town mpg will go down to as low as 30 around town in the coldest Nebraska winter of about 0 deg, and especially short trips.

The mpg will go up noticeably after getting up to 32 deg outside temp, but will still be lower when they are driven for shorter trips.

Turn the heater off and mileage will go up. (gas engine has to run to put out hot water for heater)

Their all susceptible to driving into head winds on the highway trips....mpg will go down to 35 to 40. (70 mph w/cruise on) Mileage will go up to near 50 + mpg, if driven 55 to 60 mph.
But will usually get about 43-46 at 70 mph with no heater, and flat ground to drive on. (tail wind can add 2 or 3 mpg)

My wife gets better mileage than I do in town, because of my somewhat lead foot. They all are sensitive to how they're driven.

I still use std oil...may try the synthetic...but the extra cost doesn't offset any extra mileage. I have found the ethanol will not to as well mileage wise, as 87 reg gas.

 

These may seem like silly questions, but how long does it take time-wise and distance-wise for the car to heat up to proper operating temps? How long does "warm-up" mode last? How many miles would it take to get to Stage 4 operation, over 5miles I'm assuming.

Just trying to get an idea of this as I travel about 8 miles to work, ave speed about 50mph, straight driving, no traffic, temps range from 25 to 35 degrees in winter, to about 80-90 degrees in the summer.
The sticker on the window says 75-80mpg so I'm hoping with some different driving methods as suggested on this forum that I'll be able to see those numbers as some point in the future. I really plan on using better driving skills and I'm looking forward to learning how to drive more fuel efficiently.