Gradual decline in fuel mileage

Try a different gas station

 

welcome to priuschat! how many miles on her? you might need a new 12 volt.

 

I agree...check the 12 volt battery. Do a search to see what we mean.

 

Very many things can contribute to an MPG decrease. Please read the following questionnaire, and reply with as many answers as practical. It will gives us a lot more hints to go on.

Fuel economy complaints/queries? Please copy, paste & answer these questions, esp. if you're new

 

Not your thread. Did you read the linked thread?

We prefer to see actual voltage numbers. Just because it is just 30 months old doesn't guarantee that it is fine.

Did you personally re-measure them recently, while morning cold? Don't trust the dealer, they may set it while the tires are warm or hot, leaving them actually underinflated.

Many of us prefer higher pressure, but that is a comfort vs. mpg tradeoff that only you can choose.

AC always on, and set to low temperature, will cause significant MPG loss in slow and congested traffic. Raising the temperature setting and reducing the fan speed as much as tolerable will help. But if reduced AC use is not tolerable, just recognize that it does cost fuel.

'Too much pollution' is not relevant. The AC does not clean it up.

Please check and report the brand and model name so others can check out whether or not it is an LRR (low rolling resistance) model.

New tires will reduce MPG a bit until they are broken in. This is in addition to any loss due to a non-LRR tire model.

 

Sorry, but the way you formatted the reply hid most of that new information.

Sumitomo is the brand, what is the model name under that brand? They make several models.

Regardless, I don't see any Sumitomos on the current LRR tire lists. So the tire choice is probably costing a few MPGs.

I had a 2010 Prius for three years, so know that it can be manually switched between Recirculate and Fresh air source, whether AC is On or Off.

With high outside temperatures, AC is certainly needed. But in my climate (not a desert), it never needs to be set to LO. 75-80 works just fine, especially when dressed lightly for hot weather. Without passengers, I also set the fan speed fairly low, and point all the dash vents at me, in order to minimize the needed climate control energy consumption. Let the back seat area get hotter, nobody is sitting there.

Do take note that over any significant length of time, the inside air will be completely replaced by outside air, even when set to Recirculate. (It must be replaced, otherwise you will suffocate as the interior oxygen is consumed by your respiration.) The ventilation system can filter out much dust and pollen, but not any of the chemicals and other pollution and smells. You can avoid the short dense clouds of pollution, but not the longer term average pollution level. So when the outside temperatures are tolerable, you may as well use the Fresh setting to avoid AC use, except for those occasional brief dense dirty clouds. Without Fresh air, sunlight heats up the interior significantly and forces fuel-robbing AC use at lower ambient temperatures, needlessly reducing MPG.

The car automatically selects Recirculate with AC, to save energy by cooling partially pre-cooled air. (This doesn't save anything when you initially get in the car with hotter inside air. It saves only after the interior is cooled below outside temperature.) But even then, it always pumps in some fraction of outside air -- whether fresh or polluted -- to prevent oxygen starvation and excessive moisture accumulation.

Did you have any other new information that I missed?

 

The Sumitomo T4 had been listed as 'low rolling resistance' but Sumitomo changed/discontinued that model. It had a 51 psi sidewall rating and is what I have on our 2003 and 2010 Prius. The 2003 is testing different tire sizes and the 2010 is running what Toyota sold us about three years ago . . . when the T4 was still in production.

Sad to say, the T4s on our 2003 are wearing out so I've order a pair of Yokohama Avids that match my criteria:

• 51 psi max pressure - this reduces the contact area and tire flex to minimize hysteresis losses. I have not found any other vendor making 51 psi sidewall, 14" tires.
• maximum diameter / minimum revs per mile - this is in effect, 'overdrive', that reduces the transmission stirring losses as well as the angle of flex between the contact area and the non-contact area.

These physical characteristics can be modeled and measured. In the meanwhile, I've given up on the term "low rolling resistance."

I appreciate that tire design and construction can reduce rolling drag but there are no metrics for rolling resistance as part any tire specification. Between California and NHTSA and Dept. of Energy, all have promised but FAILED to deliver rolling drag metrics. I don't fault those who think this term has merit but challenge them to cite a coefficient of drag or actual rolling drag metric for current production tires (i.e., California and NHTSA both published some initial study results 10 years ago!)

Bob Wilson

 

i think the mass tort solved all these problems, didn't you get the

i think the mass tort solved all of these problems, didn't you get the memo?

 

49 on the highway and less around town tells me your battery isn't doing much. you should be under warranty which will save you as much as $4,500.

 

My 2010 has over 132k miles and has consistently read over 50 mpg on the computer. I live in the mountains and work in the desert. Mostly highway miles at 70 mph. I've never changed the battery.

 

same here! except for the miles, mountains, desert and mph parts.

 

Maybe calculate what you're getting for a few tanks. You seem, at least in part, to be at the mercy of up-and-down mpg display in the dash.

 

mercy!