Help! with gas-milage problem

Uhh, "oil change [...] at local Chevron station".... what is the oil level now on the dipstick? Did they use the correct weight? Grossly overfilled or incorrect oil can hose MPGs.

 

We have a 2007 Prius with 72,000 miles. We were getting 50-55 mpg on the original Goodyear Integrity tires in "good weather". We got about 46-48 in extreme hot or cold weather. We replaced the Goodyear's with Bridgestone Turanza EL 400's at 40,000 miles and the mileage dropped by about 10%. I used to rotate the Goodyear's myself every 5,000, now have Firestone rotate them to maintain warranty (80,000 miles). They drop the pressure to about 32 pounds everytime the rotate them, despite me telling the to leave them at 42 front and 40 rear. No matter what we do now, can't get the mileage over 50-51 in "good" weather and 42-45 in "bad" weather. Going to Michelin's next time, I don't want to junk good tires, but I don't want to wait another 50,000 miles either.

 

How can your Prius be getting 45-50 mpg when mine is getting 38-40 mpg?

 

Because your commute and or driving style is different would be my guess.

My normal commute only allows me to maintain a 45mpg avg. but if I stay out of the foothills and drive on flatland then my mpg averages 50mpg (over full tanks).

 

Yep. manlyprius, can you please copy, paste and answer the questions from http://priuschat.com/forums/gen-ii-...answer-these-questions-esp-if-youre-new.html?

You mention "Some tanks are all highway, others city, some both" but we know nothing about the length in time and distance of these drives. It also sounds like you changed the tires and wheels. As part of answering, please specify what you changed to (size and tire model) and when.

 

What is your average MPH as shown on the display? Do you think you could be driving faster? I know it might seem like a rudimentary question after everything you have looked at/done, but I find it very easy to drive faster unless I pay attention to it.

 

Unfortunately, the 2nd gens have no average speed indicator.

All we've got are these two screens relating to mileage:
http://commons.wikimedia.org/wiki/File:Prius_mfd_energy.jpg
http://en.wikipedia.org/wiki/File:Priuslcd.jpg

These are from the older/low res display but the newer high res one that became available on starting w/the 06 model year don't show any more info with respect to these screens.

 

The most recent oil change was by my local Melbourne, FL Toyota dealer service about 800 miles ago. I can only hope the oil they supplied is the correct weight. (The mechanic at my local Chevron station is way better than Toyota's parts changers by the way. The only reason I took it to dealer "service" is the mpg problem.) The dipstick readings are: after sitting overnight 1/4" above the top dimple dot. After running the engine for 2 minutes and letting it sit for 1 minute 1/8" below the top dimple dot on the dipstick. There has been no significant change in mpg after this oil change. The screen showed 39.0 MPG when I brought it in and it shows 38.6 MPG now.

 

All of my driving is on the east coast of Florida, which if you've not been, is as flat as a pool table. My house sits at 17-ft above sea level. The dune across the street is the high point at 22 feet above sea level.

I don't exactly feather foot it but I'm not slamming the pedal to the metal either. I keep up with traffic and merge onto the freeway as I would with any vehicle. My driving is about half around town doing suburban errands of about 5 to 10 miles, sometimes with 3 passengers, and half trips on the freeway that are 50 to 200 miles by myself. MPG is about the same either way.

 

My driving is about half the miles around town doing suburban errands of about 5 to 10 miles, about half the time with 1-3 passengers; and half trips on the freeway that are 50 to 200 miles by myself. Some tanks are used all suburban errands, some are all freeway, and some are combination. Either way the MPG is within 2 mpg regardless.

The tires are Goodyear Assurance 195-50-R17 installed in May 2009. There was a 2-3 mpg drop when I changed tires from 49~51 with the stock tires to 47~49. The drop from 47~49 to 38~39 happened in November suddenly and for no readily apparent reason.

 

Thank you for answering!

I see a few problems:
Part of your mileage drop is due to the colder temps and possibly winter fuel blend. I remember hearing on the news that earlier in the year, Florida was having record low temps. (http://www.usatoday.com/weather/news/extremes/2010-01-11-florida-cold_N.htm covers your last 3 months.) Your suburban errand driving is likely hurting your mileage too. I'm guessing that it has a bunch of stops and isn't just a straight shot w/o a single stop.

You've changed to larger tires but I can't speak to the rolling resistance of them off hand vs. the stock tires. (Someone else can chime in).

Your oil is overfilled. Try to siphon/drain it out so you aren't over. Do you know what viscosity they put in?

As for your HVAC settings when it's chilly, that's another problem. When the ICE (internal combustion engine) is cold, I recommend NOT using auto or any of the fan on positions at low speeds and idling. Set the temp to max (hi) and turn the fan off when the ICE is cold. It'll keep the ICE from turning on/staying on to provide cabin heat, which is wasteful at low speeds and when stopped. You'll still get some cabin heat coming in due to ram air. Only turn on the fan once the ICE is required (for harder accelerations and speeds >=42 mph, where the ICE must run anyway) or once the ICE is warm.

Since you mention windows down, you might want to close them. Having them open creates extra drag.

I would consider getting your alignment checked too.

(I'm on original 12V still and have no experience w/one going bad on my Prius, yet.) From the post cited, it sounds like your 12V is unfortunately, marginal. However, I can't speak to the accuracy of the 12V "should be" values as I didn't write it and the questions about the 12V were added by one of the moderators. Hopefully, someone can chime on on this.

As for ethanol (never could avoid it when I lived in CA), I can't speak for the credibility of these pages, but it looks like it become required/hard to find gas w/o ethanol in FL. That could further explain some of your drop.
http://www.fuel-testers.com/florida_ethanol_news_e10.html
http://green.autoblog.com/2009/06/19/ethanol-free-gas-a-hot-seller-in-florida/
http://domesticfuel.com/2008/05/05/florida-requires-ethanol-use/

 

manly, when did you buy the car?

Did *anything* else change or happen around the same time? New driver? Started carrying a kayak on the roof rack? 300-lb guy joined your car pool? Car drove over an alligator?

The oil level should not be above the full ("do not add any more") mark. Even if there is no apparent immediate effect on MPGs it will increase the chances of fouling the MAF, and that will certainly hurt MPGs. (Always check the dipstick yourself before driving away from every oil change. This can expose some amazing mistakes before they become annoying or expensive.)

 

Thanks cwerdna.

Correct, my suburban errand driving hits a traffic light every mile or two. But its the same errands I was running before the mileage drop.

Wow so the dealer over-filled the oil. Isn't that nice. Should I check the transaxle too?

I'll check the battery with a voltmeter and get the alignment checked. Any special tips for Prius alignment?

 

Well now that you mention it, a gator was chewing on the fuel line one morning. Nah, same ol same ol as far as I can rememba, which is not as far as Pepridge Farm. Except for the 40 bars of solid gold I stashed under rear seat, I remember that. I think July 07, odo is at 43,000 miles now.
How could it be these so called professional certified factory trained mechanics put too much oil in a car?

 

Bad dealer service departments exist. Some here can attest to them. While I wouldn't necessarily call them bad, Central Toyota in downtown Los Angeles overfilled my oil one of the times I went there for a change.

 

I don't know but it's pretty common. I just got my first service done and they overfilled mine about a quater of an inch too. My guess is that it's one of the following two reasons. Either they add a pre-determined volume (which is a little too much because the old oil isn't fully drained) or they add the oil and check the levels straight away (before it's all made it's way down to the sump) so it creeps up another 1/4 an inch after they stop filling.

In any case I'd say they probably know about it but think it's either benign or a good thing. Since excessively low oil is worse than a 1/4 inch overfill, and some people will go severce to service without ever checking the oil level for themselves, then maybe they think it's prudent just in case an engine happens to had a higher than normal oil consumption.

Personally I do check my own oil levels and I would rather they just fill it to the top dimple like it's supposed to be. For the record I haven't notice any drop in FE since i've had the service (about 3 weeks ago).

 

Update on my frustrating '07 Prius poor mileage problem. 47,000 miles. Tried 44 psig in tires, not much improvement in mpg but rough ride. Wheel alignment showed toe 0.10 / 0.15 adjusted to 0.05 / 0.05. Mileage up from ~41 to ~43. Checked 12V battery voltage, OK. Then back down to 41. Filled up with Ethanol-Free, up to 45 ... but $3.28/gal. Took it to dealer service, did a full induction / fuel system service for 300 bucks, checked brakes, oil change. Mileage was up to 43 for the first tankful and engine was smoother, then down to 39. Back to dealer, they reset computer and calibrated fuel gauge. After 4 tankfuls average is 37.1 mpg, and now my fuel gauge reads "F" even after driving 100 miles - it was accurate before.
SOC indicator has been in the low charge purple area more and more, and in the full charge green area less and less. Looking at instantaneous mileage while driving, I've noticed the "highs" are not as high or as often. No more 60 ~70 mpg while cruising flat .. best it ever gets is ~50.
Can't fix it. Can't sell it .. a 37 mpg Prius is like a Lexus with wood seats and no A/C.

 

How was the 12V battery checked? (The Prius should be turned off, maybe let it sit awhile, then just put a voltmeter across it). Seems to me the HV battery is dropping too much, and either it is bad, or it's trying to prop up a weak 12V battery and drains itself in the process, which causes the gas engine to run more, lowering your mileage. 4-6 years is the typical life for a 12V battery.

 

Using the Vehicle Signal Check voltage over night is 12.0 V. Pressed brake 11.9V. Charging 14.1 V. I'll check it again.