10 years of MPG in the high 30s...What can I try?

With 140k on the ODO it might be a good idea to clean up the MAF sensor with some MAF cleaner, sometimes that can get you a couple of extra MPG.

That 12V battery also sounds like it could be going south, after letting the battery sit overnight measure it with the vehicle off.

After balancing my HV battery I saw about a 3 or 4 MPG increase.

Though it won't really improve your MPG, you might want to drain and fill the ATF WS fluid (assuming it wasn't already).

 

New Traction Battery did not cure my low MPG
https://priuschat.com/index.php?posts/2564544

VVT Oil Filter? Poor MPG'S?<br />https://priuschat.com/index.php?threads/81138/<br /><br />VVT Oil Filter? Poor MPG'S? Clean the vvt sensor an......


It all in here 34 to 50mpg

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Pretty sure Torque can tell you a bunch of things once set up properly and when you 'log' the real time results while driving around.

That said, my cheapo Elm 327 BT device doesn't allow me to read the HV battery resistance for some reason -this could also be a user error on my part, as others don't seem to have this problem.

You might want to look into a 'mini vci cable' and the 'techstream' software, which needs a windows laptop (or similar).

What sort of codes have your logged and or cleared so far?

 

Do the vvt first huge Difference glides much better way more power then i buy ebay cheap coils i had good luck with the cheap one pack of 4 battery show full charge way more. I really thought it was the battery but after the huge boost haven't even check it after i bought the odb2 tester

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living in the climate you do, i don't think you can expect much more. heat is a hybrid killer. there may not be a warmer place on earth.
i think it's amazing that you have gotten 10+ years out of the battery. i would sell the car, or put a new battery in.

btw, your 12v is virtually dead.

ps, you are supposed to change your oil every 5,000 miles. you have a maintenance schedule in the o/m.

pss, the 16" defenders have a lot in common with your poor mpg's.

 

The tires you have a not LRR/ULRR, they are Standard Touring models and rolling resistance is a BIG factor when trying to eek out those last few MPGs.

Clean or dirty MAF will have virtually zero effect because these cars use Wide-Band Oxygen sensors (WB HEGO) for Air-Fuel-Ratio (AFR) control. Therefore, even if the MAF signal is WAY off, the ECM will adjust to keep the AFR in the specified range (speed and load dependent), which is typically about 16:1 for lean-burn applications where FE is the primary goal during cruise.

Having said that, if the WB oxygen sensor is tired, it WILL affect FE. One clue is the long-term fuel trim, if it is too far off 0%, it suggests the sensor has lived it's life or been damaged by the use of silicone somewhere in or on the engine.

Last thoughts are the driving style plays the single biggest role in FE, I consistently get 10% better than my wife around town, regardless of which vehicle. To say I drive conservatively, would be an understatement. Secondly, increasing tire inflation pressure will not off-set the substitution of standard tires for LRR or especially ULRR tires. This is mostly a highway speed FE impact, FWIW.

 

Answering the original question in the subject header: Why start now; especially if it involves spending a lot of money (new set of tires,etc)?

You can either slow down or just live with it. When I had my G3, I got 46-50mpg driving mainly a 35-60mph route while my wife got 39-41mpg on her 70-75mph route.

Edit: also, I skimmed the other posts and didn't see it mentioned but you have a 10 year old HV battery that is getting weaker and weaker which means the engine runs more and more=lower mpg.

 

sounds like o/p has more time on his hands to finally try and diagnose and fix the problem, now that he is driving less, and the problem of low mpg is less important.

 

Since this has been the case for some time, I doubt that is a factor as the numbers have not changed.

 

His own experiences should tell him this already.

And I agree that it is WAY too late to be worrying about this anyway.

It likely will get worse.
And at that point the only "fix" might be a new car.

 

you can expect something if the engine has to run more to charge the hv battery which is constantly charging the 12v through the inverter.

but a bigger concern is getting stuck somewhere when the 12v quits. edit: 6-7 years is getting close to the finish line. test it after the car is off, and has been off for a few hours. if it isn't 12.4 or better, you can try charging it, but if it won't hold, replace it. the computers don't play nice when the voltage gets too low.
it doesn't matter how long others have had their 12v, it only matters what condition yours is in. and in the southern heat, many replace them at 4-5 years.

 

Not really, our '05 does that routinely.

 

If you have 15 minutes to spare, this is a test I usually do with my friends, when they're struggling to reach their mpg goals. Do a 70 mph test run on the 16.8 mile round trip, interstate portion of your commute on cruise control. I'd do the test on a weekend, or a slow period. The key is using cruise control to take the human element out. Stay in the slow lane because if the speed limit is 70 mph, you'll be among the slower drivers. Do it at a time when you can keep the AC off.

It takes you nearly 4 miles to reach the interstate, so the ICE should be warmed up. Again, it's important to keep the cruise control set at 70 mph- the lower the better. You must do a round trip to account for changes in elevation. Start the tripometer at the beginning of the highway portion and end it at the same spot on the return.

If the tripometer reads 50+mpg over the 16.8 miles, then the problem is probably related to driving habits. If the tripometer reads 38 mpg, then there is something mechanical that needs to be addressed.

 

Being fairly new to Prius and the forum, I can only state that at continuous driving at 70 mph or above, my mileage can drop to the low 40's. Continuous driving on long stretches at 55 mph gets me 45.5 to 46 mpg. I also notice that stop and go driving in the city really drops my mpg. But yet my hv still runs in the green sometimes. I am finding that speed, driving habits, and circumstances do affect mpg more than I thought.