Are my current MPGs normal?

Thanks for answering the questionnaire!

Your 12 volt is likely just about done. I'd charge it up w/something that doesn't charge faster than at 4 amps and see if it retains a significantly higher voltage than that. If not, replace it.

Don't use auto (I almost never do) and manage your heater use better. See the section I wrote on that at Why mileage gets worse in winter | PriusChat. Your cold temps are hurting your mileage. It'll get better when it warms up. I would grille block due to your temps being so low. At minimum, block the upper portion of the grille. One can do it easily by stuffing it with pipe insulation.

 

Remember to take advantage of braking. Braking is a recharge system. Traditional driving would say to coast towards lights and not over accelerating. From everything I've learned on this site and done myself the breaking to recharge is significant. It keeps the battery more fully charged so when you use EV MODE you can travel a greater number of miles before depletion.

Also......... Use the EV MODE. There is an art to it.....don't over accelerate. Be prepared for it to kick off at 25 mph. When transitioning to from 25 to higher speed and thus ECO MODE I attempt to have my acceleration at a "sweet spot" where I am in "the zone". You can actually gain mpg by using EV MODE after being stopped at a light and beginning travel again.

Temperature is a huge factor in mpg. Temps here range 10-35 degrees F in winter. (upstateNY) Mileage is around 36-40. During the summer months I can achieve 50-60.

 

I agree, I would think your battery is pulling your MPG down. It takes the engine running more to keep up the charging process. I read somewhere that trickle charging, like 1.5 - 2 amps, is your best chance of reviving a consistently low battery. If that doesn't do it, it's shot. As it is it's just a matter of time before it puts you down and it could happen anytime, and usually at the worst times. Depending on your tolerance for risk you may want to take the safest and surest approach.

If we didn't drive it daily I would think about a battery minder to extend battery life. But I'm thinking driving it is the best way to keep it charged. I wonder if charging more would be helpful.

 

I too agree that your 12 volt battery is weak and should be replaced soon. It is a DIY if you are mechanically inclined. Just make sure you get the correct battery. The battery has smaller post's than normal, also it is vented and is a AGM type. There are about four different brands out there that I know of. Yellow Top, Toyota True Start, Exide, and a battery that O Reilly Auto Parts sell. I believe all four of those are drop in batteries. Also, if your car does not have SKS on it, and you buy a Yellow Top, you will probably have to change the battery tray to make the new battery fit properly. You can purchase the tray from Toyota.

I also agree that you need to employ better A/C - Heat management. If you run the system on AUTO all of the time, the electric A/C compressor will also run. That will drag down the mileage some.

One other thing I note on your survey, your trips are rather short. The Prius really does not get to top efficiency until it has fully warmed up. It takes a good ten to fifteen minutes to fully warm everything up. If your trips are short (15 miles), you really are not enjoying the optimum efficiency that the Prius can deliver.

As the weather get's warmer and drier you should see your mileage improve.

Enjoy your Prius and good luck to you.

 

OP has a Gen 2 Prius. No US Gen 2 Priuses came w/any EV mode button. The EV, power and eco buttons are all NEW to the 2010+ model year Prius. US Gen 2 Priuses have none of those butons and no Gen 2 Priuses have any eco nor power mode buttons.

The general wisdom here is that it's not a good idea to accelerate so slowly from a stop (in normal) drive in EV only, due to conversion losses. All the energy ultimately comes from gasoline. Pulse and glide makes sense, if the pulse is via the ICE.

As for your mileage, well, the Gen 3 (2010+) Prius has a better EPA mileage rating than the Gen 2 and most here agree that the Gen 3 gets better mileage.

OP might find Car and Driver: The Truth About EPA City / Highway MPG Estimates | PriusChat interesting. Yes, a 15 mile drive in cold weather mean the engine isn't warmed up until much of the way into the trip.

 

^ Yeah, but you can slip into EV still, think it's referred to as Stealth Mode. In the (3rd gen) manual they suggest to lift off the gas completely, then gently re-apply. Maybe 2nd gen not as easy?

 

Yes, one can generally get the ICE to shutdown if you pulse then glide while below ~41 mph. See http://www.cleanmpg.com/forums/showthread.php?t=1224.

Problem is, there's no indication on Gen 2 as to whether the ICE is on/off. One can monitor it w/tools like ScanGauge II to monitor ICE RPM. Just because one's coasting below 41 mph doesn't mean the ICE is off (even w/the heater off). I've seen cases where it runs below 41 mph, heater off, ICE (well, FWT aka Fahrenheit Water Temp) is at a reasonably value (somewhere above say 155 F) and I'm not going down a hill w/full battery.

At very slow speeds, it's easy to hear if ICE on/off. When moving at 30+ mph, it's impossible to tell by sound alone.

 

Are you intending to track your fuel economy manually? Winter is the toughest season to see what the car can do. Look through the grill blocking threads & buy some pipe insulation. It'll be the best 3 bucks you spend on the car.

If you wait too long you'll come up to a dark car one night. You may be able to get it to boot up on the third try. If you've gone this far the trip should be to buy a 12v battery.

 

In reference to the grill blocking, most recommend that you get a scanguage II to monitor the temperature. The Prius does not have a temp gage, only a idiot light. It has been said that when the light comes on, it is too late. Other's may have a different opinion. I don't grill block, but am considering it. However unless I get the scanguage, I will continue to not grill block. Yes, it does get cold down here in Houston, and yes the grill blocking would help. So far, I have just accepted the drop in mileage through the short winter's here and enjoyed the overall MPG.

Also, when I changed the battery in our Prius, I went with the Toyota True Start. So far, no problems. Only time will tell. Whatever battery you buy, make certain it is fully charged when you get it. It should measure 13.0 to 13.1 volts when it is fully charged with a digital volt meter connected directly to the post's with NO load on the battery.

Good luck to you and enjoy your Prius.

 

I have not experienced any overheating. The ScanGauge has many uses. Inverter pump failure is more likely. I did lose 3 pieces over 5+ years from the top. The top is compression fit & I pushed one right through the grill on my first install. The other two mysteriously disappeared. The adhesive does melt or migrate so they will stick a little bit to the car.

They are chunks of soft foam that are not travelling at supersonic speed. They would end up sitting on the underpanel.

The bottom tubes are tied on. They aren't going to come off the car unless the front bumper cover is also ripped off.