from 50 to 45 mpg in 1 week, what could be wrong, looking for advice

I am guessing a High of 43 Low of 37 is making your engine work harder to stay warm.

(Never jump any car with the Prius, doing it wrong can cost $4000. Buy a $40 jump pack instead)

 

Did your last tank coincide with all the rain we have had in the last week? If so, the rain offers another level of resistance and could explain the drop, especially if you are traveling at the same speed and all other factors are constant.

 

As the above posters said, precipitation and colder weather have a noticeable effect on fuel economy.

Your battery level is also potentially concerning. Considering you have such a long highway commute, your battery should not be dropping that low overnight. I'd keep an eye on that and check it every morning. If you see it at 2 bars or lower most mornings, that could be the first sign of a failing traction battery. And that would also have MPG implications. However, the lower bars may also be a temporary result of using your Prius to jump-start your wife's car, so no need to panic unless it's happening regularly.

 

If your Prius is a gen 2, you are expecting too much from it. The mileage numbers improve with each successive generation. Even with a gen 4 Prius I struggle to get 56 MPG in the cold 30F weather. I am happy with 52 or 53 MPG. If a gen 3 owner could consistently get 50 MPG in the cold weather, that would be impressive.

Your mileage is pretty impressive for gen 2. I would suggest getting a gas can and fill it with a gallon of fuel. Test your computer and run it down to empty just to make sure your on board computer is accurate.

 

calculate your refills manual each time, and keep a running average. they info is much more accurate than the screen.
also, you have a gen 2, with a fuel bladder which can cause issues.
how old is your 12 volt battery?

 

Rain and cold weather take a toll on gas mileage. The 2008's are at the 10 year battery age milestone.

Did any new laws change gas blends in California ? . . . Registration fee up 25%. Some license plate fees up 25%. The sales and use tax decrease applied to diesel fuel but not gasoline.

For whatever reason, my 2005 gets consistently higher 3-5 mpg with Shell than with other Top Tier brands.

 

Actually, according to others here who have tested, you would need 3 gallons.

 

I live in the Bay Area and my fuel economy can fluctuates between 43 to 51 mpg between tanks. My commute is exactly the same every day. Unfortunately, I don't think you can measure fuel economy to better than ±10% across and two tanks of fuel. There are too many other variables still affecting fuel economy like weather, traffic, your right foot, etc.

 

There's been a ton of rain in California for the past couple of weeks. That's probably the problem. It affected my MPG too.

 

rain will knock a couple miles off my ev range, even at low speeds.

 

Thinking Big Battery, too.

Also I have had more MPG fluctuation with fill ups. I almost exclusively get gas at my local citgo. It's a busy station so it's mostly fresh gas to the station. But some fill ups are better than others. All things being equal. Weather, tire pressure etc.

But I have a lot of miles on her. (260,000) So think she gets particular, lol.

 

Lots of things can affect mpg
1. Running Ac/heat
2. Weight car is carrying (includes spare tire/junk in trunk)
3. Tire pressure
4. Air conditions (cold is thicker, wind)
5. Oil used
6. Fuel used. (ethanol fuel has less energy so the higher % the less mpg)
7. Driving high speeds
8. Short trips (engine needs time warm up)

 

I have had huge fluctuations with fill ups as well. I guess variance in when the gas pump stops.

Solution might be to fill up at slowest setting so fuel doesn't backup into tank but i don't have patience to wait longer each time.

 

stockdaddy - Re: "Solution might be to fill up at slowest setting so fuel doesn't backup into tank but i don't have patience to wait longer each time."

Try thinking of it this way. That extra 2-5 minutes you spend filling up slowly allows you to put anywhere from 1/2 to 2 more gallons in the tank. Your impatience at the pump is actually making you spend more time at the pump. 2-5 minutes at the gas station will get you an extra 30 minutes to 2 hours on the road behind the wheel instead of prematurely heading back to the gas station.

 

Damn. That makes sense. Kudos to you. You've just saved me time and money.

 

You're welcome.

 

In my Gen 4 I noticed a 10 mpg drop (best guess) on a trip from Phoenix to LA that was entirely on wet (sometimes very wet) freeways. It was the first time I have seen rain on the whole trip which I do once a week. AC not needed, for sure. But the drive was in the power range a lot more.

 

This is cool! I always get gas at the same citgo where I get morning coffee. It's also the cheapest, near me.

But since Uberring
has been taking me to far flung places, (LOL, in CT., that means yer out of state if ya drive an hr in any direction) I have been buying gas at more expensive places. My fuel use has been better by about 7%. And with a lot more highway miles!

Gonna have to do more in depth research but lovn' this!

Any one else think there are better gases to be had? (insert spouse's jokes here, snork)

 

We just make sure we stick to top tier gas.

I keep a log in the glove compartment as well as on my phone and on fuelly.com. Gas mileage has remained pretty much the same between Chevron, Arco and Pilot/Flying J. As a result we stick to Arco (for the lower prices) locally and Pilot/Flying J truck stops on our interstate travels. Chevron (higher prices than the others) is only used when we're in a pinch and the others aren't convenient.

Other top tier gas companies might yield better mileage results for the driving I do but for me these choices are good enough.