Help with 2008 Prius MPG

sorry, i don't have any clues for you. but i thought i would let you know that i have been getting the same consistant mpg on my 08 for 3 years. so don't give up until you find out what's wrong no matter what the dealer says. all the best!

 

What tires are you running?
What psi in those tires?
What oil do you use?
What is the oil level?
Is the cabin air filter clean?
Is the engine air filter clean?
Alignment could be off.
No mods to the exterior?
No significant cargo weight difference?
Any chance you drove on $4 2008 gas with a greater awareness of fuel use?
Clean MAF sensor and throttle body?
On a level road, what is your impg at 40, 55, 65 mph with a warm car and no wind?
When you put the car on jack stands, do all 4 wheels spin freely (in neutral)?
Does it glide like it used to under 42 mph? (no arrows)

Just some thoughts. Good luck.

 

she could definately be having a negative effect on mpg. whenever drivers share a car and % of sharing changes, it can make a big difference.

 

That's interesting because not getting green too easily is actually an indicator of a good traction battery, the opposite of what you're thinking. On normal highway driving without any significant hills I don’t expect to get a green SOC. The better condition your traction battery then the more likely you are to see the SOC sitting nice and stable on 6 blue bars most of the time.

One thing that will generally result in seeing less frequent green SOC is a more gentle driving style. Typically a more aggressive driving style with harder acceleration and harder braking will result in more green SOC action, while an and overly gentle driving style (too much trying to keep it in glide and trying to gently accelerate using only electric) will cause the average SOC to be much lower. It’s interesting that the both of the extremes here are bad for fuel economy, and that the overly gentle style can be the worst of all!

So it’s just a thought, but are you trying too hard?

Going down a hill of half a mile or more that requires no gas pedal to keep speed and requires a bit of light braking to maintain speed. This will normally be enough to see a rise of at least one bar of SOC. Do you see the green arrows going down hill. Do you ever see your SOC increase when going down hill. Surely you do?

 

Don't worry about mpg while gliding or coasting unless it is NOT 99.9. The engine is off (spinning without fuel use above 42 mph), so mpg is really undefined or infinite here.

Focus on steady (or DWL) speed mpg on a regular course you drive. This should produce a trip mpg in line with established norms of mpg vs mph. If you use Trip A for tank mpg, use Trip B for these tests. Someone can probably provide a link to a bobwilson4web chart, for example.

If the engine shuts down when it should/has, and steady mpg is ok, then things are probably ok, more or less. Before you air up the tires, do a glide-down from say 40 mph from point a to point b and note your speed at point b. Air up the tires to 40 or whatever up to 44, and repeat. You should (given equal wind) have more residual speed at point b at higher psi. Of course, steady mpg should be reduced from norm if it is not gliding well. It should feel free, like neutral, with no negative g feeling if no brakes are dragging. Use neutral for the glide or feather the throttle to a no-arrow state.

 

I read with interest Spamhead's mpg decline which I have also experienced with my 2008. Until June 2010 I was enjoying 50+ mpg. Since new tires and routine service in June 2010, I'm struggling to maintain 43 mpg. The Toyota dealer says it's been a common complaint and blamed it on the summer gas blend. The tires are the same size as the originals with advertized low rolling resisitance and my gas source still tests ethanol free. Maybe this is normal operation for when the Prius exceeds 30,000 miles? In spite of this, 43 mpg is much better than the 18 mpg avg. I experienced for 5 years with the Jeep Liberty I traded in. However, when I'm ready to replace my 2008, considering this mpg decrease, I'm not sure if it will be another hybrid.

 

Same size but what brand. Low rolling resistance is a relative term, they might not be as low as the originals. Please state the brand and exact model of the tires.

BTW. Most people suffer a loss of a few MPG's after getting new tires, even the exact same brand/model, but they get them back after the tires "break in" in anything up to 10,000 miles. You could be suffering from a combination of the new tire effect plus a somewhat higher rolling resistance tire as well.

 

You will take a big hit with those tires. More pressure will help. Max. the cold setting. Your dealer is probably using 5-20 or 5 - 30 wt. oil. You should switch to 0-20 wt. oil. Toyota brand is probably as good as any. H

 

The new tires are Falken ZE-912 P195/55R16 87V. The original tires were Bridgestone P195/55R16 86V . Toyota corp. claims new tires have no impact on mpg.

 

The new tires are Falken ZE-912 P195/55R16 87V. The original tires were Bridgestone P195/55R16 86V . Toyota Corp. claims new tires have no impact on mpg.

 

Many users here have reported an initial loss of a couple of MPG with new tires, that they subsequently got back as the tires were worn in.

The tire choice definitely has a big impact on MPG. See this test for example where there's a 7.5% difference, even in just a very limited test where all those tested were relatively low rolling resistance tires. : When Round and Black Becomes Lean and Green

If they had of tested a wider variety of tires they would have found even bigger differences in MPG.

I'm sure those are good performing tires, but low rolling resistance apparently isn't one of their strong points. See the following and download the document "Boo" links in the first reply. The Falkens ZE-912's score in the second lowest category for rolling resistance.
See : http://priuschat.com/forums/gen-ii-...-falken-ziez-ze912-tire-review-nice-tire.html

So I guess you could be losing about 5+ MPG because of the tire choice and then maybe another one or two that you might get back as the tires wear in.

 

Also, (there's a link to it in the article uart pointed to) Tire Tech Information - Tire Rolling Resistance Part 3: Changes to Expect When Switching from Worn-Out to New Tires mentions mileage decreases from even using identical tires as replacements for worn out ones.

 

When I purchased the Falken tires in June, I relied on CR that recommended them based on good ratings for rolling resistance and wear. Now in October, CR's ratings are poor.

 

I don't have access to the (June 2010?) CR you quote so I cant really comment on that. Could you post a screenshot or something.

Wrong rhetorical question. The CR report posted in the linked thread was from Nov 2009.

Several reviews I've read have listed rolling resistance as not being a strong suits for that tire. You put on the tires and your fuel economy dropped. It's not rocket science to figure out what the cause is.

 

That and the wife could be an added problem. What does she do when she drives? Jam the pedal? Try to creep in all electric? Does she make short hops to/from work? Even if you get great milage, if she gets subpar then the whole tank's going to dip.

But my bet is on the tires too. New tires mean bad economy for the first few thousand miles anyways, any tires. Now that you have not so good LRR tires, they will never be as good. Probably better traction, but definately not as good FE.

 

All of sudden, with the last fill up from where I always buy gas (no ethynol), my mpg has returned to 52 (was 42). If new tire break-in was the cause, I'd expect a gradual improvement. Same with using a greater inflation psi. I think it all depends on gasoline blends: winter, summer, etc. The gas I've been using since the June melt down has been ethynol free as substantiated by a H2O test.