05 MPG down to 35...what's wrong?

http://priuschat.com/forums/gen-ii-...-answer-these-questions-esp-if-youre-new.html
http://priuschat.com/forums/gen-ii-prius-fuel-economy/99504-why-mileage-gets-worse-in-winter.html

 

Thanks, but that got me nowhere. I was looking to see if there was a common problem that would cause a dramatic reduction in MPG in such a short period of time ... apparently not.

G

 

No, but without sufficient info, we can only throw out guesses, which isn't very productive. Ideas include: shorter trips, much colder weather, bad 12 volt (if you're on the original, it's bad), tire changes, underinflated tires, bad alignment, overfilled oil, poor heater use management, etc. Please answer the questionnaire if you want help.

 

A history of overfilled oil makes it likely that you need to clean the throttle body if you haven't lately.

Also check the right rear seatbelt to make sure it's in the guide that keeps it from blocking the vent used to cool the hybrid battery. And go back to parking in shade instead of parking in the sun. And take all those gym weights out of the trunk that have been there the past few months.

Are you using the same tire pressure guage you always have? Digital ones are more accurate, consumer reports found that other kinds are usually way off, sometimes by as much as 10psi.

While the remove the fuel injectors and clean them method is doubtless more effective, it is much cheaper to buy a bottle of fuel injector cleaner add it at your next fill up and see if it helps.

All that said timing wise it does sound like the broken inverter coolant pump may have either damaged the inverter before being replaced, or maybe something is wrong with the replacement pump that is leading the cooling fan to come on and drain power. (that coolant loop tries to stay a lot colder than your engine coolant loop and it's harder to get the temperature data from it.) Wash the bugs out of your radiator maybe, inadvertent radiator blockage would force the cooling fan to come on.

 

Most common problems for the magnitude of decrease that you have seen:
1. Bad 12V battery. Works just barely to start the car, then requires max charging current while in use.
2. Change in drive pattern. Instead of 35 miles each way, average trips are 3 miles.
3. HV battery weak. Constant demand from the HV battery computer for recharging current.
4. Tires/wheels. Installation of 17" tires on custom wheels.
5. Roof Rack. Aerodynamics compromised by rooftop luggage carrier.

 

Effect of cold weather can be huge also.

 

^^this!! I learned this today as i looked at my info screen to see my prius getting 37mpg! :O

but I let her warm up at least 7min each day to defrost the windows now that I wake up and its a sweltering 36 degrees out

time for some grill blocking

 

Interesting thread but the OP hasn't posted to it in almost a year. Seams like beating a dead horse unless he is still asking for help. I did read the entire thread so I guess I can beat on it a little while I'm here.

I had to look up his tires as tirerack doesn't sell that brand (note Toyota is using a tire by this company on the new v "wagon").

"Toyo Proxes 4" 215/45ZR17 91W 21.6 lbs 24.8" diameter 8.4" width 1356 max load 50 PSI max UTGQ 300 AA A 839 Revs per mile.

Given the revs per mile of that tire if the OP was using the MFD to check MPG it's still going to be optimistic (the display is 5% to 10% optimistic at 855 RPM so it should still be 3% to 7% optimistic at 839).

I know it's not the likely cause of his unexplained drop in MPG but if he were to look for replacement tires I'd jump on the 844 215/45/17 Michelin Primacy MXM4 with Green X as the replacements.

I really hope for Ken's sake that he isn't dealing with an inverter or traction battery issue. My best wishes to him coming back and telling us it was something cheaper to fix.

 

Sadly telling us enough to give informed advice is too hard. You want advice based on nothing.

Based on nothing, the best improvement to MPG is to drive as if you had no brakes.

 

I've been noticing this same thing on my '05 prius with 120K miles.
I have Toyota spec tires. (@40PSI) I still drive exactly the same places as always. The same gas. I don't use the AC at all...

The *only* thing different is that my average milage used to be 45-48MPG but now I can't get over 40.

The main focus of my attention has been watching the distribution of the energy on the Display. What I'm seeing is that the car rarely utilizes EV power...
My HV battery (according to the display) Never runs down past two bars.

In city driving, at low speeds the Gas Engine does almost all of the work and I'd imagine that the milage I'm getting is commensurate with any other small car with a 1.5 liter engine.

In other words, on streets that I used to accelerate to 30 MPH then feather my gas pedal to maintain that speed with EV, now I can't get the EV to take over and the gas engine is still providing power to the wheels.

I've read the whole thread and I'll check the 12V battery and the HV air duct etc. But I'd like to know if this is a common thing with older Prius models.

 

The 12v battery problem is very common on older Prii. Check it thoroughly and get back to us.

I swapped mine out for an Optima unit years ago and have never suffered the type of mpg drop that others with bad 12v batteries have.

 

If you are on the original 12V, which is what 7 years old now, you should just replace that out of hand. Otherwise, check it carefully. The HV battery is really hard to diagnose without using a scan tool. The HV battery fan running is often an indication. It basically should never run on high unless there is a problem, and if there is a problem, then, most likely, a module has had to vent gas and is now weaker.

The 12V battery problem is extremely common, the HV battery will get weaker with age and you might be seeing those symptoms.

 

Hi wesg, you haven't shown your location. Are you northern-hemi southern-hemi or tropics? What sort of temperature are you in?

I've had trouble making the car use EV mode when the traction battery has been too hot. But you can also get the problem in cold weather if the engine is cold and/or if the climate control needs to make heat. The climate control is always on, you cant turn it off unless you manually dial the temperate down to "max cold" and set A/C to off.

You say you checked the ducts, did you disassemble it to the point where you could check/clean the rear fan? This helped for me.

Also, are you familiar with the 4 stages of hybrid operation? The Gen2 Prius has some quirks regarding when it will and when it wont cut out the engine, so it will really help if you familiarize yourself with this aspect. You can probably find it if you search on "modes of hybrid operation" or I could dig up a link later.

 

Its been a long time since I posted my query. within a week of that post, I changed out the OEM 12V battery for the yellow top and that helped a lot. During this past winter my mileage was once again in the low 40s high 30s, but that I attribute to cold weather and no insulation in he grill of the car. Turns out, that helps the milage a lot in colder weather. (I'm in Chicago.)
Tomorrow I'm letting the dealer inspect the car (152,000 miles now.) so they can give me a trade-in value against a new 2013. I was considering the Persona series, but after re-reading all the 17" tire-talk I might change to a 3 model with a sunroof.
I can't *wait* to hear about all the bad things wrong with my car. (In order to lower my trade-in value.)