Poor MPG, dealer said to change bearing

http://priuschat.com/forums/gen-ii-...-answer-these-questions-esp-if-youre-new.html
http://priuschat.com/forums/gen-iii...mileage-gets-worse-in-winter.html#post1411488

Can't help you w/your bearing issue.

 

To test the 12 volt, go through http://priuschat.com/forums/newbie-forum/73400-weird-stuff-happening-mpgs-dropping-test-battery.html after the car has sat overnight.

 

What was happening to originate a vibration? Turning the wheels? Or try to make a wheel wiggle?

 

Start by doing some manual (litres used, kms traveled) calculations, the MFD result might be off. You may need to average it over several tanks to get an accurate measure.

When I first got my S/H prius the displayed consumption was mostly around 5.5 to 6.0 L/100km, but when I actually measured the litres and kms and did the manual calculations it was actually under 5. Interestingly over time the displayed value got more and more accurate, and now it actually reads just a little bit optimistic, but still pretty close.

 

When it is cold outside, the engine cools off faster, so it has to run more.

0.2 - 0.3 l/100km difference at least is to be expected with winter tires, especially at your under inflated pressure.

The more electric you use, the worse your fuel economy will be.

You don't have to... Your answer doesn't make sense. Warming it up or putting the HVAC on a high temp makes the engine run more, and reduces your fuel economy. You are using some litres per 0km which means you get 0 averaged in. That is never good.

You really should read your manual. You only have 4 modes in the Prius. Park, Neutral, D-Mode which is normal Drive, and B-Mode which is engine braking.

Also, you are getting about 40mpg. In what world is that poor for using winter fuel in -7C weather?

 

Any energy lost has to be made up by running the ICE (Internal Combustion Engine) more. Heat is lost faster in cold weather.

Most of us run at 42 PSI in the front and 40 PSI in the rear (as long as that is below the rated MAX of your tires) to get better MPG, Treadwear and handling

Any energy used from the battery has to be replenished by the ICE (or indirectly via regenerative braking). The process of saving energy in the battery and then taking it back out is not terribly efficient which is why he said to try to NOT use electrical energy and save MPG. The main benefits of our Hybrid Synergy Drive (HSD) are:

1. The ICE can be smaller - More MPG - without sacrificing overall performance and can be an "Atkinson Cycle" engine
   1. Higher peak efficiency
   2. Low torque at low RPM but the electric motors cover this flaw
2. Regenerative braking to avoid wasting energy when slowing down
3. Always operating the ICE at a high efficiency operating point

Actually a combination of both in B.

JeffD

 

Korozive - Give this a try for a week or so - forget that you are driving a hybrid and drive it like a regular car that you are trying to maximize fuel economy with - still be gentle on the gas (but not overly so) and think ahead to avoid heavy braking. I know that it is a bit counter intuitive, but your mileage might tick up a bit.

Another poster converted the metric to english and said that you are getting around 40 mpg - to me that is about the low end of what I expect. Here in Philly it has been in the 30's to 50's for the last few weeks and I'm seeing mid 40's. My tires are all seasons that are a year old and inflated to 42/40. I'd figure the tires and the colder weather up there are good for a few mpg's and a bad wheel bearing likely would bring it down a bit further.

 

At low speeds the engine has a hard time maintaining proper operating temperature when it is very cold out. As such, when you come to a stop light or you are gliding (engine off) to a stop or down a hill, the engine will either remain running when it wouldn't normally be running if it was warm out or it will cut your glide short by turning on the engine to warm back up.

e.g. On my work to home commute I drive down a long hill (1,200ft. to 250ft. for about 6 miles). In the summer months I can glide down a lot of this hill with the engine off. In the winter when it is <40Fdegrees I can only glide for so long before my engine temp drops so low that the engine turns back on. This drops my mpg from 9999 to about 150mpg. That is a pretty big difference in total mpg and how it contributes to a lower number on my tank average. The same can happen when gliding to a stop light/sign. In the warm months you may be able to glide for up to a mile before coming to a stop but in the winter the engine may kick in much earlier and ruin mpg.

Were they the same tires? Different tires will exhibit difference rolling resistance characteristics. Depending on the tires you could lose 4+mpg just by switching models/brands.

This has already been covered above but remember the laws of thermodynamics! You cannot transform energy into different forms with suffering a loss. So using battery power which is derived mainly from gasoline requires an extra conversion which ultimately leads to a loss of overall MPG. Use the gasoline engine more and glide (no engine, no electricity) as much as possible.

Accelerate briskly to get up to speed. Then lift off the throttle and reapply gentle pressure to maintain desired speed. Buy a ScanguageII to assist you in finding the sweet spot for acceleration. Many have found that accelerating briskly is better for mpg than driving super slow off the line.

This could be another issue with the tires being different (if they are) and new. It could also be a bearing issue. I've never had a bearing failure so I don't know much about it's affect on inducing extra load on the vehicle but it makes sense.

 

have to go with 12v, they tend to die when it gets colder.

 

If you look at the battery and it's not an optima yellow top it should be.

If your wheel bearing are shot the noise and vibration would be evident.

As it's cold A)your gas tank bladder has shrunken stealing 2 or 3 gallons of room, that will skewer your calculations. B)10%+ reduction in mileage due to cold weather, everything turns harder.

Snow tires are going to cost you 3-5mpg.

Is your emergency brake hanging up?
Are your ice air filter and cabin air filter clean.
Is your oil 2/3rds up the dipstick and not overfull.
Possibly an intermittent firing spark plug.

 

Remember that the Prius is supposed to slow down to some extent when your foot is off the gas, even in "D" mode. Sure it's more pronounced in "B" mode, but there's definitely a "by design" simulated engine braking in "D" mode.

Korozive, can you confirm that you get an "engine braking effect" in both "D" and "B" mode, with the "B" mode effect being about double that of the "D" mode. Perhaps you are somehow effectively stuck in "B" mode all the time?

 

WE are telling you to replace your battery based on your test. 11.1V at Ig-on is a severly weakened battery. It is within 0.5V of not starting. There's a good chance the DC converter is maxed out trying to charge that brick, and that extra energy has to come from somewhere.

If the technician could not demonstrate axial play in the bad wheel, then I don't believe the wheel bearing diagnosis.

 

I wouldn't trust the dealer. We have had many people come in here and say the dealer said their battery was fine but when they checked it themselves with a digital volt meter and found they had less than 12.2v. IMO anything below 12.2v is time for a new battery.

 

if you dont trust us then go on google and lookup what normal and BAD voltages are for your 12 volt battery and you will see....11.8 is not that good.
then tell you dealer that you never return there

 

+1, a wheel bearing bad enough to cause a serious fuel mileage loss would be making a lot of noise and then shortly self destruct.