Help! with gas-milage problem

I checked the battery voltage again this morning, after the car sat all night. Used two voltmeters. One reads 12.60 V, the other 12.67 V. Good enough?

 

Probably. It doesn't seem low enough to explain low MPGs.

You don't do anything oddball, right, like shutting the car completely OFF at stoplights, or leaving it ON for a half-hour while you buy groceries or wash it, or something?

Without seeing your driving style I think I'm at an end.

The shop manual says to add 3.9 quarts, which is simply too much (3.9 quarts is the *dry* capacity of the system including filter, and some always remains within the engine, and some of them round it to 4 quarts). Three quarts even is plenty.

 

IMHO my driving style is "typical" or "normal" meaning no oddball stuff, not a Hypermiler nor Racer-X. I'm thinking its the MAF fouled by too much oil. How do I check the MAF?

 

I'm far from an expert, but since it's been almost a week with no reply, I'll TRY to answer.
I too have a 2007 Prius, and avg only 44 mpg consistently no matter what I do. If I ever got close to 50 mpg I think I'd wet my pants.
I checked my MAS myself. Take off the air filter cover. Remove the air filter. Underneath you will see a hole with a little wire-thing sticking out of it. CAREFULLY spray special MAS cleaner...(nothing else), red can cost $7.00 at autozone.
Only spray a little bit on it, as too much will screw up your car. There is a little bulb at the end on those wires...it is supposed to look a bit cleaner after doing this, if it was dirty.
Mine was not dirty, and looked the same after I did it, so I kinda wasted $7.00. This stuff dries before your eyes. Don't overdo it.

I'm a newbie, so hopefully the other smarter guys will chime in here and correct me if I was wrong at all.

Frank

 

I've watched my mpg keep dropping the same unexplained way. Started new at 48 to 50 mpg, 46, 42, 38 ... now I'm lucky to get 36 mpg. Yes, yes I have answered all the PriusChat questions, checked and double checked all the suggestions (thank you all but none worked), even had dealer service go over it on three separate occasions (they are useless by the way). Despite all the PriusChat advice and countless hours and money I have spent ...... my mpg continues to drop. At the rate I calculate it will be 31 mpg by the end of the year. Frankly, I can hardly wait to sell the car ... it will most definitely be my last Toyota product. Unfortunately for me: who will buy a Prius that gets only 30 mpg? Free to a Good Home: 30 mpg Prius.

 

^^^ I haven't re-reviewed your previous posts carefully, but if you're serious about free, I'm sure there are MANY folks here who would take a 2nd gen Prius for free, despite the supposed mileage problems you're having.

Can you take the Prius onto the highway after the engine has warmed up and then drive a steady speed somewhere between 55-65 mph and reset the MFD? Use the cruise control and drive a few miles, then get off and go the opposite direction to help cancel out the effects of wind and elevation change. Please report the speed you maintained and MFD's mileage.

Your changing to 17" tires and wheels didn't help and can exacerbate the apparent mileage loss due to odometer and speedometer calibration being off.

 

Ok you probably tried a lot of things, how about your A/C if its a few oz low the A/C will work harder (spin higher RPM's to do its job_ use more AMP's = use more gas ) The lower your refrigerant gets the more AMP's the electric compressor draws. Some times after the compressor has been running it self to death but but still working because of low refrigerant small particles of metal flakes wear off the compressor and start plugging up the condenser but not all the way just enough to raise the high side pressure= high AMP draw. Even after a A/C service the high side will be high because many of the tiny small tubes will be plugged, the A/C will work but you will still have poor gas mileage and a A/C not working 100%.

 

Until he reports back with data from the test that cwerdna suggested there is really not much to go on.

 

ok then I did the test on a stretch of flat highway at 55 mph on cruise control, typical warm humid sunny Florida day, windows up. My speedometer reading matches within 1 mph of police radar. I've attached 3 photos of the display. Before fill up, it reads 35.9 mpg after 324 miles of about half interstate and half in town errand running. A quick check 324 miles on the odo with 9.0 gallons on the pump is 36 mpg. A reset and I'm driving south on A1A for 2 miles -- 60.6 mpg ...hmm never seen that before. Next another reset and north on the same stretch of road back to the spot I started from -- 54.3 mpg. Average 57.5 mpg. Interpretation?

By the way ... the Prius handles more like a sports car with the new wheels and tires ... than like a golf cart. A definite thumbs up.

 

Interpretation: It sounds like your Prius is getting pretty normal mileage on the highway. That means we need to focus on what you are doing off the highway to get such bad mileage.

Tom

 

Your bigest problem is your honken huge tires.Imagine taking a large tire and trying to spin it in a tank of water as compared to spinning a small tire in the same tank of water...which tire spins easer????Think of air as water.. the orignal prius wheels have those plastic hub caps to keep air out of the wheels so they spin easier..An orignal prius tire with hubcap will spin easier is said tank of water compared to orignal prius tire without hubcap..Did you remove some of the oil that was 1/4 inch over full on dipstick...that was taking at least 5mpg off your milage.The oil should be about 1/8 inch below full mark taken in the morning before engine gets started...Your large tires and air swirling rims are good for at least 6mpg against your milage......

 

What he said. I put 17" factory Scion rims and 1" wider tires on my Prius and dropped about 6 mpg. With the mileage you report getting during your highway test, there is absolutely nothing wrong with your car!

 

^^^ I've been careful with the oil overfill since then, but only a 2 mpg difference. So, I paid big money for a sophisticated hybrid drive when all I needed was to swap the normal-size road gripping tires on a Yaris for a set of lawn mower wheels? Silly me.
Seriously, if you check my posts you will see the wheel / tire change out accounts for about 4 mpg of the 14 mpg loss I have experienced. The improvement in handling and driving enjoyment was profound.
At that time I also discovered the speedometer calibration was about 8% slow with the stock setup, which means the mpg display was higher than my real world mpg. However, right after the new wheels / tires, with proper oil level, and with calibration -- the MFD average was in the 45 to 47 range. I'd be overjoyed with it today.

 

I'm having the same problem with lower MPG's ....... AND I'm running
205 45 17's ... soon to swap back to 195 65 16's (stock size - touring) my best average is 44 and my worse is 42 ... I'd be tickled pink if it jumped back to the "normal" range ...... BTW the handling is FAR superior with the 17's

 

Try weighing the 16" wheel/tire combo before you put them on and weigh the 17's after. The 17's are probably MUCH heavier and that rotational mass can have a big effect.