2009 Prius in Florida 33 mpg

Since you report both good and bad tank averages, it can only be environmental. I suspect the bad tanks are due to things like more short trips or high speed driving

 

AC will kill Gas mileage

 

I found that if you drive the car harder it gets better gas mileage. I have a 2011 Prius

 

Congrats on the new-to-you buggy. Sorry it's not performing very well. A couple things come to mind.
One is your statement about your battery.

I assume this is the 12V auxiliary battery. The display is not a valid test in my opinion. And you didn't say if it was "Ready," "On," or "Acc." If it was in Ready mode, that's not a test of the battery. I suggest at least checking it with a multimeter after the car sits overnight. Better yet, use a load tester.

Next thing I wonder about is how your driving conditions vary from tank to tank. I'm assuming that you are calculating mileage the old fashioned accurate way with the gallons and miles. 33-36 mpg is really bad, but even 44 in the city is not stellar. It is OK, though. Are you making lots of short trips on the bad tanks? Excessive stop and go from highway speeds like on US19 or 54? Those are horrible, especially when the lights repeatedly force you to brake hard at the last second. Getting stuck by another wrong way driver head on collision traffic jam on the Howard Franklin will also waste a ton of gas.

In other words, there are just too many unknowns for anyone to offer a theory what has much chance of being helpful.

 

Not THAT much!

 

Where do you buy your gas?, found I get better mileage on certain brands of gas, Sams Club, for instance has consistantly better gas and I suspect it is less ethanol, that up to 10% ethanol could be the culprit, also an additive such as PRI-G can save you some mpg but I can only find it on Amazon. Your throttle body could be dirty too, spraying cleaner down it can mess with the computer so taking it apart my be the solution. Try a couple tankfuls of ethanol free gas, don't know why they charge $1.00+/ gl more for it but they do. Tennessee it can be found same price, or a few cents more per gl. The EGR Valve could be a culprit, you didnt say how many miles you had on yer buggy.

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i just put new tires on my 08 and I lost 5 mpg, no idea why..down to 41 ish ... cant return them so Im not going to worry about it.
when they say a car can hit certain MPG thats under perfect test conditions with a brand new car...
its very deceptive but thats the car business

 

Put more air in tires, try 42/38

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Wifey gets consistantly 63 ish with her 16 eco, I'm getting 42.5 actual in the v while the dash gestomator says 45

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+1000 On the tire psi at a min 42 psi.

 

Forget miles per tank, the Gen2's flexible fuel bladder is sometimes problematic and leads to short 'tanks'. Keep filling up no later than 2 bars on the gauge, and focus just on MPG.

For your MPG issues, have you reviewed this thread?: It covers most common problems except brake drag:

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

 

You can't make sweeping statements like this. For example, for my tyres, 42 PSI is grossly over-inflated. Sure, over-inflated tyres might net better MPG, but at the expense of prematurely wearing out your tyres.

I can't run over 36-37(Front)/34-35 (Rear) PSI without my tires wearing prematurely around the centres. If your tyres show this wear pattern, it means they are over-inflated. Over-inflating your tyres will cause them to wear out prematurely and whatever cost savings you make using less fuel will more than be compensated for in additional costs in replacing tyres before you would normally need to.

The fine tuning to know what is the correct tyre inflation pressures for any car/tyre combination, can only be done on an individual basis by visual inspection.

Use a tire depth gauge of some description – whether a basic analog one or a fancy digital one – as it is almost impossible to spot a 1 mm (or 1/32") difference in tread depth between the centre and edges by eye.

 

Are you using steel belted radial tires? At least in the U.S., that center wear pattern from overinflation is more a characteristic of (old-fashioned, obsolete) bias ply tires than of steel belted radials.

 

LOL , that is too funny Fuzzy.

Haven't seen bias ply tires in decades.

It happens with modern "steel belted radial tyres", but most people don't get up close and personal with their tyres these days, let alone with a tyre depth gauge, so it goes unnoticed. Except for the wondering why these tyres have worn out after only 30,000 miles.

 

@dolj Go to simpletire.com and buy some michelin energy saver A/S...You wont have problems after that no matter what psi you use.

 

Plenty of hypermilers (try CleanMPG.com back in its glory days, a decade ago) do get up close and personal with their tires. That even caused me to get and use a tread depth gauge.

And those hypermilers are the greatest proponents of higher pressures and longer tread life.

 

You can also measure some tread depth using a penny and a quarter. From the Goodyear website:

"The Penny Test
There are several popular ways to check your tire tread depth. One easy way is the penny test. Simply insert a penny into your tire's tread groove with Lincoln's head upside down and facing you. If you can see all of Lincoln's head, your tread depth is less than 2/32 inch and it's time to replace your tires.

The Quarter Test
Another easy coin test is the quarter test. Insert a quarter into your tread groove. If the tread touches Washington's head, you have at least 4/32 inch of tread remaining."

Check Tire Tread Depth | Goodyear Auto Service

To see if the tire is wearing evenly just use the coins to measure the outside, center and inside grooves on each tire.

 

I don't have problems with my tire, but thanks for the steer. However, Michelins are a niche brand in this neck of the woods and are such a price premium that, in the long run, they cost more than they save.

 

I don'y really have an opinion on that and am not saying that it is not true – in some cases.

My point was that you can't make blanket statement to use X PSI as the pressure is individual to the car and tire combination that is used. It is up to the owner to monitor and adjust accordingly. If you care to. Some people just don't care.