Same Prius, Not The Same MPG

We need more information before suggesting remedies:

typical trip profile?

Bob Wilson

 

I have also had a big (I thought) dropin fuel mileage. MY 2010 has 19K on it. For about 18K the mileage ranged from 47 to 52 on the computer,and 45 to 50 by calculator. A couple times i got 58-60(computer), 53-56(manual) during some controlled short trips. These trips were 80-100 miles flat road and not placde to be in a hurry.

required questions:

I use computer and manual(calculator). Computer is always higher... as the mileage goes up, the computer gets more exagerated.

I expect to get the estimated 48hwy 51 city. I live in the Panhandle of Florida. Flat terrain, warm weather, and no real city driving. Traffic is mild, and you can keep speeds averaging 25-40 mph (on computer)

Temps are in the mid 80s to mid 90's. consistantly

I have a steady routine of 18 miles to my job. I use the car all day easing around parking lots as I work on apartments, along with a daily trip to Home depot. In addition, about once a week I make an 60 mile trip up the hwy to the inlaws. This trip entails one light on either side of the 65 mph hwy. My mileage has not changed on the hwy trip at all. If I baby it, I can get 51 mpg, but most of the time I move along 65-70 mph and get 48-49mpg

The battery is 6 months old and I checked the voltage with a volt/ohm meter at 12.96 volts first thing in the morning

I had the alignment checked at the dealer today. It was good. Mechanic said he tweeked it a little but really didn't need to.

My average speed in normal driving is 27-35(avg on comp) posted limits 35 mph and 45 mph not a lot of lights. When I make the hwy trip comp puts avg at 55-60. I don't hypermileage, but I do like to make a game of trying to better my mileage.

As mentioned the terrain is flat

I have raised my tire pressures from the recommended 35/32.5 to 40 front and back since I started loosing mileage--no improvement actually continued to fall.

I changed the oil about 3K miles ago, it was a little over full, so I drained 1/2 court out last week, and put it just under the full line. Again no improvement in mileage

I have a 2004 matrix, it stays around 29-31 in the same driving. 2005 corvette stays 22.5 around if I stay out of the gas, and a 2006 Trailblazer, getting 17-18, but I only us it to pull a 5X9 open trailer.

I initially made no changes in my driving habits, thinking it was a bad tank of gas. But since then I've incorporated most of the suggestions in this forum.

I have used the AC on auto every since I got the car. Auto/Recirc 74-77 deg

Factory tires, and no modifications to the car. I rotated them and balanced them 3K miles ago

My daughter hit a curb, but no damage. I've lifted it and checked all the panels--they are in proper locations.

Now my situation... When my mileage started dropping, I noticed My battery indicator appears to be lower every time I get in the car. I don't have daytime running lights. I used to get in my car, back it out of my garage, down the drive way and be in Drive for a few seconds before the engine would start. (that's different than I hear other people saying) Now, the engine starts as I'm exiting the garage. The battery levels are lower almost all the time. It now takes my whole trip to work (18 miles) to get them up, used to be about 1/2 way.

It appears that the charging system has develped a problem that is hurting efficiency. Bottom line is the engine runs more, the the batteries charge less.

The service manage at the dealership has no idea what is wrong. I brought it in with the computer mileage reading an all time low avg of 33.1. He was more concerned with the break recall than the mileage and avoided the conversation until I cornered him. He said the alignment was ok, and everything looked like it was operating properly. He said the speedometer (off 2 mph--high of course), and the computer mpg (regularly off up to 5 mpg) are just estimates.

Same old bull you get when they don't know what's wrong.

Any guidance I get would be greatly appredciated. I really need something to bring to the dlr next week, when I leave it for his "fuel consumption test" Thanks

 

followup questions

Thanks for giving us a bunch of details.

I can understand your temps being in the 80s to 90s now, but was it that way when you first got your car? I doubt it, esp. since you have 19K miles on it.

As for engine runs more and all, well, if the AC compressor has to run more often and at faster speeds, it WILL put a bigger load on the car and drain the HV battery more quickly and I believe, it can prevent it from charging as quickly. I attribute some of your mileage loss to higher AC duty cycle.

Regarding expecting to get EPA mileage estimates, please read http://priuschat.com/forums/other-c...uth-about-epa-city-highway-mpg-estimates.html.

I'm confused about your statement "no real city driving" as I feel it contradicts "I use the car all day easing around parking lots as I work on apartments, along with a daily trip to Home depot". I suspect that a lot of this "easing around parking lots" entails very short trips. When you park the car, the ICE is cooling down and your short subsequent trips are killing your mileage they're not sufficient to warm it up. Efficiency is very low at first w/a cold engine.

What viscosity oil did you use?

Please elaborate it on what you mean by "baby it". Are you so light on the accelerator that you're trying to avoid having the ICE run?

 

You've repeated these tests and the results are? One of the reasons I did these tests on the drive home from the dealer was to establish a new car baseline:

This is not far off from what we get in Huntsville, AL, in the Spring, Summer and Fall. Tennessee river bottom and valleys are close so no problem with finding flat land. Yet we're also near the Piedmont so we've got a some handy hills.

It would be great if you had the alignment numbers. I also baselined my alignment and have a Firestone life-time alignment. I'll assume the alignment was checked after the curb hit.

Was it a front or rear tire hit?

What gas do you use? Testing in Huntsville revealed Shell, Exxon and Chevron were the higher energy gas, pre-ethanol. I have not repeated these tests other than to test 'home made' E-30 (not worth it.) In more temperate climates, we have gone from winter to summer blend which can have an impact.

We have the first year of a new model car. We can't rule out a potential, latent defect in the battery management software. The modules are great but we are dealing with the first year of a new model.

Is the car parked in the sun or shade?

If you want to replicate my test protocol:

• warm-up the car - drive about 15-20 minutes
• turn off A/C or other major loads - early morning is best test time, avoid high wind days, over 15-20 mph
• set speed using cruise control
• reset trip meter, do not touch accelerator or brake during test
• drive at least 10 miles and record the trip meter values
• turn around and repeat the test in the opposite direction for same distance (or close enough)
• average the two trips and share the results for that speed including temperature

Everyone who bought the new ZVW30 Prius are pioneers and likely to find the early problems like the brake pause. It is also likely there are other latent defects that have yet to be diagnosed so I don't dismiss the reports of others. What I do bring to the party are my new car baseline, what our ZVW30 did when it left the dealer.

Changes to our car:

• 5,000 miles transaxle oil change - it was tested and the straight-line viscosity change suggests a 15,000 mile initial life. We're at 12,500 miles and I'm planning a second change at 20,000 miles
• spring replacement with Sumitomo T4s - we had a nail hit a previously repaired spot. After looking at all the options, we kept the best tire on a full-size rim and put four new Sumitomos, 51 max sidewall, on the car
• 5k oil change, 10k tire change, planning 15k oil change and tire rotation, 20k transaxle oil change

Bob Wilson

 

Thanks for your quick replies.

I'll try to answer CWardna's questions first.

Cwerdna
As for engine runs more and all, well, if the AC compressor has to run more often and at faster speeds, it WILL put a bigger load on the car and drain the HV battery more quickly and I believe, it can prevent it from charging as quickly. I attribute some of your mileage loss to higher AC duty cycle.

I agree that some drop is expected when more electricity is required. (cycling of the AC) But, The AC has been on and cycling every since I bought the car, until this mileage drop problem. I only turned it off when this problem started. Yes, it was 70's - 80's and sometimes colder than that, but since this problem I have driven the day without AC to test, and I only saw a couple mile difference. Now, I didn't run it for a tank full or even a 1/4 tank. Just for the day--you can imagine 80s and 90s with the windows closed. ( didn't want to have the "AC on windows down" debate). Just as a side note, Yesterday it was 77 degrees. (I guess a front from the storm that was down in Mex). Yesterday's numbers did not change.

Regarding expecting to get EPA mileage estimates, please read car and driver article
I'm familiar with your point, but I'm trying to explain a drastic drop in mileage. Besides, where I live should be the poster area for ideal driving conditions. When I said no hills, i wasn't stretching the facts. This place is flat. There are two stop lights between home and my work. I don't travel at high traffic times, (if you can call it high traffic times here Another thing to mention is that I went through the winter with no significant drop in mileage. I read the stories this winter about members mileage dropping from cold weather, I didn't have that problem. My car is garaged (I couldn't claim it is totally environmentally controlled, but heating/cooling vents are in it) So, the outside temps should have very limited effects on initial start up. (summer or winter).

I'm confused about your statement "no real city driving" as I feel it contradicts "I use the car all day easing around parking lots as I work on apartments, along with a daily trip to Home depot". I suspect that a lot of this "easing around parking lots" entails very short trips. When you park the car, the ICE is cooling down and your short subsequent trips are killing your mileage they're not sufficient to warm it up. Efficiency is very low at first w/a cold engine.

When I said no real city driving. I was talking about waiting at stop lights, signs, having people push you to get moving, and all the other things that you have to deal with in city driving. I've lived in cities from new york to Bali, and this is not city driving. Those factors have a strong impact on driving practices, when compared to "easing" from one part of the complex to another. But, again, there has been no change in my driving habits.

How much do you think the ICE system is going to cool down in an hour or less if it is 90 degrees outside. Check under your hood after an hour when it is 90 out, the radiant heat from the compartment dissipates at a very slow rate. Typically if you have a cooling issue you have to raise your hood before you get any real relief at those temps.

What viscosity oil did you use? I used 0-20 w synthetic

Please elaborate it on what you mean by "baby it". Are you so light on the accelerator that you're trying to avoid having the ICE run?

Yes, easy on the throttle, to keep it in ECO range or below. I tried to use the EV for this travel when I first got the car, but it never really saved and fuel. It would just kick out when the batteries dropped and the engine would run almost continuously to charge the batteries back up. In the end it wasn't worth using EV. However, when I tried to experiment after the mileage started dropping, I tried to revert back to using the EV again. It is almost never available. I don't know if it because a problem with the charging system, or what. But the conditions are never right. (I think the EV mode is more of a marketing tool or toy than anything else)

Bwilson

It would be great if you had the alignment numbers. I also baselined my alignment and have a Firestone life-time alignment. I'll assume the alignment was checked after the curb hit.

I didn't get the numbers, but he said it was within specs; he only "tweeked" it.

Was it a front or rear tire hit?
I didn't hit the tire, the curb hid the cowling under the front bumper.

What gas do you use? Testing in Huntsville revealed Shell, Exxon and Chevron were the higher energy gas, pre-ethanol. I have not repeated these tests other than to test 'home made' E-30 (not worth it.) In more temperate climates, we have gone from winter to summer blend
Is the car parked in the sun or shade?

I used a shell station near my house "almost" exclusively" until this problem started. I tried chevron accross the street and generic mom and pop (one each) to see if any difference was noticable. No change in that area, Unless they are changing the
mixture as you mentioned. But my wife-vette, daughter-maxima; son-matrix have had no problems. I have everyone check there mileage every tank. I was tought that is the first sign of impending issues.

I hope I've answered all the questions. But, I'm sure that the Svc Mgr and the regional mgr (i'm fully expecting to get "that's the way it is" from the dealer) so I'll have to elevate it. I think in order to satisfy everyone and head off Toyota's hot weather answer, I'm going to have to bite the bullet and run a tank with no AC (whewwww) to have the numbers ready.

Also, has anyone heard of the fuel consumtion test for the Prius. I just don't see how they can test fuel consumtion with the cycling of the ICE.

 

As I stated before, the higher outside temps (but unchanged auto climate control temps) will cause the AC compressor to run faster and more often. Using ScanGauge II on my Gen II, idling w/ICE off is draws ~1.2 to 2 amps (at ~220 volts). IIRC, when the AC compressor is running, we're talking at least 4.x-9.x amps. If I put the fan on high w/a somewhat warm cabin, I see the 9.x amp drain.

The ICE DOES cool down significantly when it's not running, esp. after an hour. On my Gen II, operating temp is IIRC corresponds to coolant temp (FWT aka Fahrenheit Water Temp) of ~180+ F. I can't speak to 90F outside air temps as we haven't even gotten to 80 F here.

I can see significant FWT drops if the ICE is stopped just for a few minutes. Today, I parked my car in about ~64 F weather. FWT went from 168 F to 136 F after just 28 mins of parking.

For your edification, you might find the first PDF at http://priuschat.com/forums/gen-ii-...angauge-best-threads-mileage-improvement.html (for Gen II) interesting along w/the corresponding Gen III version at http://priuschat.com/forums/gen-iii...-discussion/76501-gen3-warming-up-stages.html. Google's a great, easy converter (e.g. Google for 40 c in f).

Unfortunately, the Gen II doesn't have any sort of eco/pwr graph (aka HSI), but, in general, accelerating too lightly so that the ICE doesn't kick in or overuse of EV button (which US Gen IIs don't have either) is bad for mileage. The electricity has to come from somewhere. From the 1st PDF:

Also see http://priuschat.com/forums/gen-iii...pulse-glide-warp-stealth-help.html#post922878.

When you're "easing around apartments" and doing your non-highway drives, how long are each of these trips, from power on to power off? How many of these do you do daily? The cooldown/power off period between each is about an hour?

If you had a ScanGauge, one could better determine what the car was doing and at what points the ICE is in warmup mode. On Gen II, stage 1a is obvious (you'll see IGN -10), high idle RPMs, combined w/low FWT.

EV mode being denied can be due to a # of reasons besides such as speed too high, ICE too cold (not in the right stage), too hard an acceleration, HV battery too low, etc.

I do recommend bwilson4web's suggestion on establishing a baseline. If it's way of out of whack, then we need to investigate potential car problems more.

Sorry, my figures are from memory as I've been driving my other car most of this week. I have no Gen III, but have observations from a fair amount of driving my Gen II w/ScanGauge. I've played w/EV mode button a bit on a Lexus HS 250h that I won a free one week test drive of.

 

Thanks for your reply. I'm in agreement with everything you said. All of those things take a toll on mileage. My problem is that my driving habits have not changed. I have tried a couple things since the big mileage drop, to no avail. For the last three days even the temps came down to 75, 77, and 82. My mileage did not come back up over these three days. I was reading all of the gas mileage threads, and some people are complaining about big drops, and others are saying they have only had a couple mpg drop. I love the car, even at the lower gas mileage, It's still better than anything else I've driven. I'm going to track see if toyota finds anything wrong (I doubt it). And I'll track it for the next year. Thanks again for taking the time to pass on your thoughts and theories.

 

Please do let us know about this part.

If you're turning on your car for a short (<10 min trip) with say a 1+ hour cooldown in between each, those each count as short city trips, in my book and are killing your mileage. I suspect the ICE fires up and runs in a warmup mode for a good part of your "easing around".

 

I'm not sure if your getting the part about my driving remaining the same as it has all along. I'm trying to understand why the mileage has dropped so significantly. It doesn't matter what I'm doing for driving. If it's the same for the last year, my mileage should be the same for the last year with some variation for rain, cold and heat. I can understand your questions if I never had good gas mileage, but I had very good mileage and then it dropped off. I'm not driving the car any different. So, I'm not trying to analyze my habits, I'm trying to figure out what has changed in the vehicle, or if environmental conditions are effecting the mileage so significantly.

If the ICE fires up and runs in a warmup mode for a good part of my "easing around" it would have been doing that all along. So that wouldn't explain why my mileage has dropped 15 miles per gallon!

 

Monday morning with an air temperature of 72F using Shell 87 E10:

• 96.9 MPG indicated, 9 miles, 25 mph - ODO ~12,500 miles, 72F
• 89.1 MPG indicated, 11.8 mi, 30 mph - ODO ~12,500 miles, 82F

Compared to last years benchmark:

I'm using new Sumitomo T4s in place of the new OEM tires. So I'm seeing ~3% decrease of indicated MPG . . . curious but not out of the range for 10F decrease in temperature. I need to repeat it in the mid-80s. I'll also need to repeat a high speed benchmark, say 60-75 mph range.

Bob Wilson