MPG Anomaly!

[TheSpoils]

I have my Prius for about 4,000 miles now and have consistently hit between 58-60 mpg on the display per tank. My all time (no reset on trip B )is showing 58.4 Curiously, my current tank with about 240 miles started a nosedive to 56.7 – 56.9 which is hardly a winks difference to some, but it matters to me. I did not change my route, temps are about the same 55-66F and no change to the vehicle has been made. I was about to check tire pressure this evening when the MFD began to inch up again to 57-57.7 but still not to the 60 it was before. Whatever happened has put a dent in the average for the tank. Has anyone else experienced this? And what other possibilities can cause this? (In addition to route, driving style, temps and PSI) I ruled out variation in gas quality because the change minus / plus FE all occurred during the current tank.
Any Ideas?

[spiderman]

Originally Posted by TheSpoils

Any Ideas?

Somebody else drove it. Happens all the time to me when my wife drives the Prius. Other than that I have no idea why. The colder temps here have dropped my FE by about 2 mpg but it was a steady decline as the temps dropped. I blocked off the lower grill and much to my surprise I gained about about a 1/2 of a mpg.

[Matt Herring]

Winter gas could be in stock now at your local gas station...this is not a myth. This combined with lower temps will certainly result in mpg loss. I'm running at about 62 mpg right now and I am usually in the 64-65 range during warmer summer months with normal gas.

[a64pilot]

Lower SOC on the traction battery during one of the first starts of the day could do it in my opinion.
SOC has such an effect on mileage it's kind of a wild card in computing mileage.
Just a little informal playing with P&G initially results in great mileage until the SOC drops, then the mileage advantage of P&G sort of goes away, to some extent.
Oh and heater use of course as well, I see your in Maine and I am just guessing there

[alfon]

Yes, I agree, winter gas formulations, at least in the past, will lower your MPG because there is less BTU per gallon.

Here in Oregon 10% Ethanol is madated year round. In the past Oregon only mandated 10% Ethanol gas during winter months.

Back in the 90's I had a 1994 Honda Civic 5 speed (VX) model, which was designed for pure MPG's.

With normal gas I would get in the low to mid 50's mpg. With Ethanol gas it would drop to the high 40's, consistently.


alfon

[a64pilot]

Originally Posted by TheSpoils

I ruled out variation in gas quality because the change minus / plus FE all occurred during the current tank.
Any Ideas?

Don't think it's gas this time.

[qbee42]

My guess is winter gas. It makes a difference.

Tom

[TheSpoils]

Thanks everyone, since my original post the FE has gone up and down erratically. After reading all the posts I started looking more closely at the outside temps. Last few days they have been dipping to 42-50 and I used the heater (front defogger). I have experience with the Altima hybrid and the winter FE hit, but for some reason the Prius seems more sensitive with temps. The Altima did not suffer till temps were in the 30'sF. I am concerned that the temps alone have affected FE drastically even before the winter formula gas hit. Thanks again, will keep monitoring the issue.

[Bobsprius]

Spoils,

I don't think you have to much to be concerned about. Here it has been in the low 30's at night and I work 2nd shift and I have used the Heater more, not Defrost but heater, and I have noticed about a 2 MPG hit as a result. I can tell you that had I hung on to my Civic Hybrid the results were far worse. About 8MPG hit in these temps, so the Prius is definitely shining through compared to the Civic. And as many posters mentioned they like to start to play with our Gas at this time, adding more Ethanol to the mix = a little rediced mileage. But all in all I see this 2010 as being far less affected by the colder weather.

[TheSpoils]

Thanks Bob, I have to chill out a little with this MPG thing. I'm holding on too tightly.