Highway Fuel Economy

It's the 65-70 MPH in the hills that is killing your mpg. Read up on the suggestions for increasing mpg on this site. You should be able to get in the 43-45 mpg range. But, your HV battery may be getting old at this point.

 

Be sure you are not still on the original 12 volt battery, ten years is a long time. So is five years.

 

If you're getting 38-39 like that, dropping back to 60 should put you well over 40. PSI at 36-42, begin slowing or stopping further back costing longer, recapture more paid for energy from regen braking that places less demand on the ICE. So, a little slower and little sooner anticipation of stops can make the difference you are looking for.

 

Well, not bad, better then anything else for the money, a new gen3 might get 48-50, 200,000 and still almost 40 on a mountainous route, if there's a scenic way and time try it sometime, but 65-70 is just to much for great mileage.
12v has to hold a charge, trans-axle needs fresh fluid, don't carry any extra weight, you gotta do what you gotta do.

 

See also this questionnaire: Fuel economy complaints/queries? Please copy, paste & answer these questions, esp. if you're new

 

+1 on the questionnaire. All newcomers who are asking questions about fuel economy should fill out the questionnaire. It helps everyone in the long run.

Fuel economy complaints/queries? Please copy, paste & answer these questions, esp. if you're new | PriusChat

 

Here are the first items that jump out at me:

I don't believe that is low enough to be a big factor.

What temperature is it set for? If LO, this would be a significant drain at these temperatures. Putting the setting into the upper 70s, and turning the fan down to the lowest speed that still provides adequate comfort, may help.

For newbies, especially on the highway, let the car make its choice between electric and gasoline. Don't try to push it into electric, as it is much too easy to get lower MPG than the car can do when making up its own mind. Get some baseline results first, then try to improve later.

 

Thanks for filling out the questionnaire. fuzzy1 above pretty much hit the points I would mention and the resolutions thereof. I will add the following.

Concerning the A/C use try the following. When using the A/C set the temperature to 76 and use the "Auto" cycle. When the recirc turns off, turn it back on. Running the system in recirculate will help to keep the Prius cooler while lowering the load on the traction battery as the electric compressor does not have to cool incoming outside air.

Concerning the driving trying to stay on electric I suggest you look into hypermiling. There is a link in my signature which will give you excellent information on it. You will get far better mileage if you employ the hypermiling technique instead of trying to drive on electric only. Note: We are talking about speeds anywhere between 0 and 42 MPH. Anything above 42 you pretty much have to go with the ICE, even though there are tricks there too that can be employed.

Concerning your 12 volt battery. Your battery is very weak and should be changed soon. It would not surprise me if you are seeing the red triangle light up briefly when you push the Power button to go into ready mode. Regardless, the DC to DC converter which is the charging system is working overtime trying to keep your auxiliary battery charged. A fully charged 12 volt AGM type (Prius 12 volt type) normally reads on the test as follows.

Aux Mode: 12.6 V and higher
Ign. On Mode: 12.4 V and higher
Ready Mode: 13.8 V to 14.2 V

Many here will recommend the "Yellow Top" battery. Other's will recommend the OEM battery that is offered by Toyota dealers. Other's still will recommend alternative type of batteries. When I changed ours I went with the OEM type battery. I was able to do the work myself with just a few tools. Don't go to the dealer and ask them to do the job for you as the battery is expensive and the labor is high too! The average price for the battery ranges from $175 to $225 and the dealer will usually charge anywhere from $50 to $125 labor for the install. There is a link in my signature file that discusses how to change the battery.

As you have already seen driving at a slower speed 60 vs 70 and higher does dramatically effect the overall MPG. When you can, try to keep your speed down. I am not saying to impede the flow of traffic. What I am saying is this, stay in the right lane of the traffic and go with the flow. When you have time and there is no other traffic around, set the cruise on 55 and let it roll.

Last point: Michelin Defender's are a good long lasting tire. However they are not one of the "best" tires when it comes down to efficiency. When it comes time to change them, consider either the Bridgestone Ecopia 422 or the Michelin Energy Saver A/S. Also, 38F and 36R is not bad. However, if you can tolerate the rougher ride try 42F, 40R. Those few extra pounds of pressure will make a difference too.

If you haven't done so, check and or replace the air filter for the ICE. Also, concerning the oil. If you are not running synthetic, you should consider it. That too should help you to achieve higher MPG. Keep the oil between the two dimples on the dip stick. Do NOT overfill as that will cause problems.

Once you get used to driving a Prius and learn how to hyper mile you should find that you will easily meet and or beat the EPA estimates.

Best of luck to you and welcome to Prius Chat!