Reduced Gas Mileage

Hmm, that is a good tire with an ok rolling resistance rating. I couldn't see them dragging your MPG down very much.

 

Im still new here with my 2008 prius but after a lot of messing around heres what I found after buying a "certified prius" that was causing mileage issues - I was in the low 30s with city driving. I dont believe in trying one thing at a time - I would rather assess and if its questionable then fix it properly.

1. Front and back end alignment - mine only needed a front end

2. Airfilter - looks like the dealer "blew it out" and put it back in which meant dust accumulated faster than it should have - put in a new one which has stayed clean. Never blow these things out just replace em - not worth trying to milk them.

3. Cabin airfilter was CLOGGED - mind you this wont cause mileage issue more than likely but I cant believe they certified it without checking the cabin air filter - my nose is happier and I use the AC less with the increased airflow so just maybe it does have bearing?

4. Tires - the set on there was mis-matched?!!? I took it to goodyear and they fixed me up with some assurance fuel max tires which are still in break-in - to add insult to injury the weights for balancing the tires were on the OUTSIDE of the tire - on the Prius they are supposed to go on the INSIDE of the rim otherwise the covers dont fit correctly and god only knows how fast that throws the balance off. I chose not to go to sidewall ratings - let goodyear decide and they kept them at the Toyota reccomended pressures so I decided with a LRR tire Im not messing with it.

5. Oil - it was way overfull and thick (cheap oil?) - drained it and put in amsoil so its halfway up the dipstick with a WIX oil filter.

6. did some testing via the diagnostics screen while driving the car and found the main battery is dumping a huge charge to the 12V battery a lot while driving - this might be normal - in fact I suspect it is - so I am not replacing it yet since it shows no sign of going dim when I stress test it. However I believe the 12V stock battery is undersized for the vehicle - a battery with a higher rating would help since it siphons off the main pack and has to run all the accessories - I would think you would need to double the capacity to get decent performance....

Finally - after all that I was still seeing only a slight rise (went up to 35) in my mpg then it dawned on me to reset the computed mileage - once I did that and ran a tank througth it steadied out at 38MPG which given that Im a new driver - driving in the southern heat, 100% stop and go less than 6 mile commutes and still learning seems really good to me.

Some might see it as overkill but from my experience with other things - when in doubt fix it yourself or have it fixed properly by someone you trust. (I trust goodyear service centers - I DONT trust toyota or JiffyLube pepBoys etc...)

Oh yeah - on top of all that - the splashguard underneath was missing (the panel you take off when you change your oil) from what I understand this also helps regulate temperature of ICE and main pack - so I need to find a new one of those.

Same thing happened to me on my Celica - why is it SO hard for jiffylube and toyota to PROPERLY remove those fastners and put them back PROPERLY? I have no problems....why do they?

The oil and filter changes I did myself - the tires I left to the experts.

And the batterypack is now green a lot - before it bounced between purple and blue - it dont stay green for long which is healthy but it should go there now and then I think.

If your main pack is dippping down to purple a lot then I would look for whats draining it - using the AC will do it for sure - and even a lot of hills will do it depending on driving style since the electric motors give a boost to the ICE under high grades and relatively low speeds. A marginal 12V battery will likely do that as well very likely.

I dont like the Optima batteries - I wish there was a better solution - it still has a lousy AH rating - there are higher AH rated batteries but some are just too big and others I dont trust the way they mark them - I think they are fudging the numbers a bit on the cheaper ones....all part of the reason why Im doing the battery last if I feel the need.

So far....Im happy with what I got so Im staying there and see how it goes for a few tanks (which is a long long time LOL)

How on earth could all that be missed on a "certified" vehicle? Easy - cause even Dealers dont know what they are doing half the time. If you find a good one stick with them - if they suck then it is usually pretty obvious - just make sure you check EVERYBODYS work after its done and before you roll out the parking lot. =-)

Notes from a newbie - take them as such....

Oh yeah one more note - before I did all that the battery pack was always blue - first time it went green I nearly panicked I thought something was wrong since I had never seen it before lol

 

Oh clarification on Optimas - I have nothing against the Optima product line - I put one in my wifes RAV4 and have had no problems for 4 years now - thing I dont like is the optima that fits the Prius is only a few AH ahead of the stock battery - I would like to see something a lot higher capacity that fits (in fact preferably a Optima) I will have to dig on the specs and see if I can DIY one of those Optima battery replacements with one of their bigger batteries....doubt I can or someone would have by now Im sure.

 

Clean out the mass air flow sensor. Special cleaner $5 anywhere. Air goes thru the filter into the mass air flow sensor. Clean sensor means more mpg
http://www.autobarn.net/maairflsecl1.html

use synthetic mobil 1. Check it after 5k mi. Change the filter at 2k for the first few times. Then only at 5k.

 

mass air flow sensor - great idea - thanks!

 

Yes. Unfortunately I have never gotten 46 mpg but I do mostly interstate driving and was averaging 41 to 42 mpg. Then I was down to 36 - 37 mpg. Initially I was told my mileage reflected my mood, but within a few months the computer readout incited that the water pump to the inverter had failed. Correction cost about 400.00 and gas mileage has come back to my usual 41 mpg.

Does anyone have experience with the 69.00 device said to improve gas mileage?

 

How fast do you drive?

We don't even have to ask which device you mean: they're all junk.

 

What are the pressures?
What's the oil level now? How do you know which weight they used?
Are you using the A/C a lot more than in previous summers? Or, is it hotter but you're *not* using the A/C?

 

You can get noticeably better MPGs by increasing the tire pressures, right up to the sidewall max. It will change the ride and handling.

What minimum voltage did you see on the 12V battery during the test?

Note that the 12V battery powers accessories all by itself only in the ACC position. With the car ON ("Ready") all the 12V power comes from the inverter; you could then disconnect the 12V battery and nothing would happen.

 

unixrocks: what a horrible experience lol. The battery size is just fine for this car, it is meant for accessory power only, not for anything else. Toyota designed it that size for a reason. A lot of threads here on the forum point out if you are experiencing low mpg, your battery might be defective. I would just go ahead and replace it since 5 years is awhile for a battery. Who knows your mpg might jump.

And if you have your car serviced by someone else, you SHOULD trust Toyota, not anyone else. What cars do you think Toyota technicians train on? All car manufacturers train their own master technicians and mechanics. They don't just hire some random joe off the street with an ASE certificate and hand him a wrench and say go to work. Goodyear technicians aren't even trained on any cars. They just require you have the certificate and you got the job. I have seen enough horror stories with quick lube places and outside mechanics that dealer work is all i do. They have the OEM parts, they know what they're doing when they work on the car, etc. Take into account that a prius isn't like an ordinary car, 3/4ths of private mechanics will probably be guessing what to do since hybrids didn't exist when they went to mechanics training.

 

Please state the make, model and size of the tires before and after.

Since others referred to a drop in mileage after replacing tires, even if they're the same model, see Tire Tech Information - Tire Rolling Resistance Part 3: Changes to Expect When Switching from Worn-Out to New Tires.

 

Yeah - I am tempted to up the tire pressure.....does that add wear to the tire?

I didnt notice the minimum voltage - I was more concerned with the number of times it jumped to 14V (meaning it is being charged) which I assume it does when it drops to a certain voltage.

 

I wish I could trust Toyota - but I havent found a dealer that I can trust.
They keep me waiting even when I make an appointment and they dont seem to know how their own software works...its just sad.

Goodyear - I should say I trust the local Goodyear service center because I talk to them and they know their stuff. I have had good luck with other Goodyear service centers as well in the past and so I am left with a "trust but verify" attitude when it comes to changing areas and going to the local shop.

I have my share of horror stories with Midas, Pep Boys etc...The last Midas managed to extract $3000+ from me with continual lies about the condition of my truck - When going througth the paperwork prior to trading it in on my Prius I remembered the struts were replaced - and there was the paperwork confirming I paid $1200 to have that work done but a quick check of the struts revealed origionals....

I hear you loud and clear which is why I am paying close attention to what all the experienced owners have to say about service, mods, driving habits etc...

On a more positive note my mileage estimator says I am averaging 42.3 mpg. I think maybe those tires are breaking in......

I really love this car - I didnt expect to really but it is so easy to get addicted to sitting at a light with your engine off and rolling out of the parking lot in stealth mode without even meaning to.

I still remain skeptical about that 12V battery.....then again I have "upgraded" 2 laptop battery packs, my electric toothbrush, my electric razor and just about anything with a battery to a higher capacity battery with stellar results so I am in the habit of distrusting OEM batteries...seems like the companies always skimp on the battery quality/capacity - again its not that you need a huge reserve capacity to power the accessories - I take issue with the number of times the system is actually charging that battery. If its charging it a lot then...I think it was best said in the movie Jaws - "Im gonna need a bigger battery"

Peace

 

Just so you know, 14 volts does not really indicate a "huge charge" for a Lead acid battery. A battery in good condition will in fact "float charge" at about 13.8 volts, meaning that at this voltage the charge rate (amps) is low enough that it can be maintained almost indefinitely in this state without overcharging. A rapid charge on the other hand would normally force the terminal voltage to around 14.5 to 15 volts. So at 14 volts a battery (well charged and in good condition) will typically be only accepting charge (amps) at quite a modest rate.

The problem of course is if the battery is not in good condition. A battery with a fault like a shorted cell for example could sustain a very much larger charging current at the nominal charging voltage. The thing is that you cant tell this from charge voltage measurements alone.

If on the other hand you leave the car sit overnight and then test the voltage before the car is powered up and charging then you may well detect a weak or faulty battery.

 

We have had our 08 Prius for over a year and initially was getting about 44-47 mpg, until last winter. It then dropped to 39 and the best average this summer has been 42. Techs have not been able to fix or explain why. The car has about 58,000 miles on it.

Last night with the mileage readout at 402 driven and 42.9 mpg, before filling up, my husband put in an additive called P.i. Performance Improver. We drove 44 miles last night before returning home and the mileage readout says we are getting 54.1 mpg. The bottle says it unsticks things that gums up. I do not know how it works, but it did. He said he ordered it from this website. I think he said it is like the third product on the page http://www.lubedealer.com/midwest/featuredproductsview.aspx

Give it a try, it might work for you too.

 

It sounds like that product will clean the fuel injectors. Can you post back and let us know if the improved fuel efficiency is maintained into the next few tanks of fuel (without additive). If so then that would make a pretty strong case for dirty injectors as a common cause of reduced FE. Keep us posted.

 

Im going to give that a try soon - normally I wouldnt but amsoil products seem really good.

 

WOW. $10 a bottle. From the specs it treats 160 gallons. Soooo you don't add the whole bottle? It's a fuel injector cleaner. Probably improves octane also.

 

Check the diagnostic page of the menu per instructions. Doesn't sound like a battery change is necessary.

I run 38/36 tire pressure some do 42/40. I personally don't want to wear my tires uneven at the price of a few mpg. 36/32 is on the door for oem pressure.

 

Increased tire pressure, up to the sidewall maximum, negligibly affects wear; it has a much greater effect on MPGs.

14V more or less means that the charging system is working. Test the battery again and write down the *minimum* voltage.

If you regularly use fuel containing ethanol the injectors are getting plenty of cleaning. One tank of improved MPGs after using an additive is happenstance.