Low mileage-- common thread?

My mileage is a tad lower than past winters too. At least part of it is attributable to the change in Gasoline Formulations.

The only thing I can buy now is E10 which simply has less energy available, and will give lower mileage.

 

<div class='quotetop'>QUOTE(MisterW @ Feb 15 2007, 10:23 AM) [snapback]390870[/snapback]</div>

You may be right on par. One of the primary contributors is driving methods and conditions.

I would try the following.
Drive your car around for a while to get it nice and warm (about an hour will do). Then find some large flat parking lot you can use as a test track. Now set the cruise control to 30 mph, reset your MPG counter (while rolling going 30mph) and drive in a very gradual circle (tight circle creates too much resistance). After 30 minutes, you should see your MPG around 60-70. Try the same thing at 5-10 mph and you should see 99.9 MPG. If a parking lot is not available, try a freeway (flat). After about an hour of driving, set your cruise control for 60 (if possible on your freeways) hit reset and drive for 30 minutes. You should get a read in the 50's assuming there isn't much wind. MPG will drop rapidly after 60 mph, so trying the same thing at 80 will likely give you low 20's to high teens (but I wouldn't know. Never taken mine over 70).

 

<div class='quotetop'>QUOTE(Dan. @ Feb 15 2007, 10:55 AM) [snapback]390993[/snapback]</div>

If you managed in the low 50s at 60 mph, I'd expect more like high 20s at 80 mph. Of course, that's assuming no wind, level highway, and little or no traffic to worry about.

Dave M.

 

AT 80MPH I have gotten 44 mpg. Recently I put E10 in the tank and dropped from my usual 50+ to 46 mph on the same mixed rural and freeway driving. Drove until very low on tank to get rid of the E10 and refueled with regulat gas and am back at 50+. From now on I will check the type of gas before fueling.

 

<div class='quotetop'>QUOTE(nwprius @ Feb 15 2007, 08:40 PM) [snapback]391229[/snapback]</div>

Holy cow! :blink: 44mpg at 80 mph is fantastic! Based on the ICE efficiencies and drag coefficient, theoretical prius models yield 30mpg.

Was that your tank average at 80 or did you reset your tank average at cruising speed and hold 44mpg as the average over an extended trip? Uphill, downhill? Crosswind, tailwind?

You could also calculate by dividing start and end mpg by your start and end miles (to get gallons consumed). But watch out, there are serious rounding errors at play and at the end of a tank the numbers can swing +/- 12mpg for short distances.

 

<div class='quotetop'>QUOTE(MisterW @ Feb 15 2007, 12:23 PM) [snapback]390870[/snapback]</div>

If your air filter has 15k miles on it, change it. Air filters should be changed at the same time the oil and oil filter are changed. Remember the airfilter will be as dirty as the outside of the car would be, if you did not wash the car.

With the cold temps of winter, heating and cooling of the oil from driving and sitting overnight can cause water in the oil. Air temps can cause water in the fuel tank by warming in the day and cooling at night.
Fuel tanks in the car and the gas station.

I work on aircraft, jet airliners, we sump the fuel tanks daily. They sit on the ground and air with water vapor enter the tank. They are fueled and take off and climb up to 35k feet where the outside air temp is around -60 degrees. The water vapor turns back into water.

I have drained up to a pint of water.

The fuel tank and oil pan on a Prius is no where as big, but the same forces are at work.

If I lived in areas that had very low temps., I would follow lower mileage and shorter time oil change limits of every 5k or 6 months.

 

<div class='quotetop'>QUOTE(DFWPrius @ Feb 16 2007, 11:02 AM) [snapback]391415[/snapback]</div>

I appreciate your experience.

I have run up to 12,000 km in Winnipeg winters with Mobil 1 0W-20, sent the oil off to be analyzed, and had very good results. No issues with condensation, no evidence of unusual residuals, good TBN, etc.

The fuel is another matter.

I used to have a 1990 Toyota 4Runner, and it had a drain plug at the bottom of the gas tank. I'd drain around 4 litres from the tank every fall and every spring, usually in Spring I'd get out a cup of water. I should have kept that vehicle, it was fairly easy to work on that way

With the Prius, the bladder makes it impossible to do any sort of extreme climate preventative maintenance. That said, it appears to be fairly common for some oil to be drawn through the PCV system and into the intake manifold.

If those sludge-like and gummy deposits coat the underside of the throttle blade, it could have an effect on MPG and performance. I speak from experience with another vehicle.

I used to have a 2000 GMC Sierra with the Vortec 5.3 motor. The first winter seemed ok, asides from the "normal" oil burning, knocking motor. Second winter around February I noticed sometimes it needed cranking to start cold, a choppy cold idle, and it had a cold flat spot/stumble.

But NO check engine light.

I was fortunate to have the shop manual, and the diagnostic tree suggested IAC and TB deposits. I took off the intake hose and manually opened the throttle blade: heavy gummy deposits on the backside of the throttle blade.

I then took off the IAC motor and noticed the IAC air passages were about half plugged with the same gummy residue. The IAC pintle valve also had the gummy stuff on it. Using 3M Throttle Body Cleaner - which states that it is approved for coated TB's and TPS electronics - I sprayed out the TB blade and the IAC passages.

On that motor, anytime you remove the IAC motor you have to go through the "idle learn procedure." Once I did that, it idled fine, started instantly again, and lost the flat spot.

So perhaps the TB system in that 2004 Prius has a few deposits in it.

 

I'll watch this post re: developments on the TB/sludge theory. Aside from brakes, which I'm sure Mr.W accounted for, he seemed to name the usual variables. But I wonder if colder temps would affect a gummy throttle plate and throw off winter mileage even more than summer. My '04 has 45K as well and I struggle to get 34 on a tank when it is colder than about 25F. I drove the car from Texas in October for about 650 miles at speeds over 75mph in general, and averaged 44. By the way, my wife's '03 civic hybrid also got 44; we bought both cars on ebay and drove back within sight of one another the whole way.
I know the previous owner did pay for a throttle body cleaning, though I thought she just went for a dealer's line...maybe there was something to it though. Dr. Fusco is one of the mileage gurus here, maybe he'll weigh in on the TB factor.

 

Just want to say: me too!

Comparing this winter to passed winters (eastern PA), my MPG is significantly worse. This is my third Prius winter and at 45,000 miles total on the car, I would not have expected things to be this different.

I guess it could be gasoline blends -- worse efficiency than previous winters.

I did upgrade the tires to Goodyear comfortreds recently too.

The only odd thing is I have observed is that the brakes seem sometimes to be sticking -- the car sometimes does not seem to roll as freely.

For all of these complaints I am lazy about visiting the dealer -- waiting for the next oil change visit to complain to the service rep.

Also, for the same tank of gas, for the same trip segment and roughly the same outside weather conditions, I can notice widely varying mileage for the same segment.

I keep seeing lots of green on the battery indicator, but people keep saying this is normal for cold weather.

The one thing that does seem to help mileage is to run with the air conditioner completey off. When I am down in the low 30's, and I am on one of my short trips (less than 10 miles) on a cold engine, I can usually coax some up-ticks on my MFD tank mileage figure by shivering in the cold.

I go a real sense that something was odd when the weather was quite warm where I live in late December and early January and mileage was unusually low. Then since it has gotten below normal for the last 4 weeks, MPG is really bad -- low 30's around town and low 40's on the highway.

Oh well...

 

<div class='quotetop'>QUOTE(jjs357 @ Feb 17 2007, 12:49 PM) [snapback]392034[/snapback]</div>

That will also have an effect. I upgraded tires before this winter and saw a mileage decrease from that too.

It really is a potential multiple whammy.

1) General increased Rolling Resistance - The Integrities have lower than average RR and if you didn't specifically shop for low RR, you probably got some increase. Comfortreds are definitely higher resistance.

2) Increased Tread Block Squirm - The lowest rolling resistance would be from slicks. Any tire that has tread blocks has some resistance to overcome as they flex. Newer tires have taller blocks which squirm more. As your treads get shallower your rolling resistance will decrease.

3) Increased Diameter - New tires of the same size are actually larger diameter than the worn ones you took off, because they aren't worn down. The car calculates mileage by tire revolutions, and the new tires revolve less times per mile, making the car think you're traveling less distance for a given amount of fuel. This would affect both the odometer and the elecrtonic MFD calculator, so they would both show lower mileage. Be heartened by the fact that this is a artifact, and not really lower mileage. In fact, if you have an extended warrantee, it is extending your mileage coverage, because you are going more miles for less miles shown on the odometer

 

Air filter 15K miles old?

I change the filter in my Tbird every 3K. I will change it in the Prius ~ every 5K.

15K is a long time IMO. If the filter is old and gets dirty, it could nasty up your MAF and your mileage drops like a rock.

 

I've kept complete records of mileage on our 2004 Prius since April of '04, and continue to do so. Our begining average was in the low 50s. Charting our mileage from an Excel file, the "log" trend has been steadily downward to the point that now, nearly three years later, our average at fill up is about 39, with the overall (i.e., three-year) average at close to 46.

We have done each 5,000-mile check-up at a dealer, with the oil and filter changed each time. I check the tire pressure regularly. Our mix of highway and surface driving has not changed.

I have also asked the dealer about the steady reduction of average mileage, and gotten the same answer, "The computer trouble codes show no problem."

I recently sent a letter and my complete Excel file (with chart) to the Toyota Customer Experience Center in Torrance, CA, asking what might be the problem. Their response was simply to give my letter a file number and send me a letter thanking me for bringing the matter to their attention. I called them, but got no where, the customer rep I talked to simply begging off, saying they had no information on this issue, and could not answer my questions, which were (1) if the engine is operating less efficiently over time, what might be done about that? and (2) could the battery efficiency be declining over time? (I have noticed that the engine sometimes is running when the display shows a charged battery, and no power being delivered from the engine to the battery.)

RonB

 

<div class='quotetop'>QUOTE(notperfectlyclean @ Feb 16 2007, 03:15 PM) [snapback]391631[/snapback]</div>

In the case of the 2000 GMC Sierra with 5.3 Vortec V8, absolutely it affected winter fuel economy and especially performance way more than summer. I probably had those deposits in summer but didn't notice any difference. Once it got cold, the first symptom was sometimes I had to crank it 5 secs before it would start.

I haven't checked my Prius TB yet. Since it has an electric TB plate, I'm really hesitant to shove something like a screwdriver to force it. I'm going to have to download the shop manual and determine if there is a proper procedure for doing this that won't hurt the electric actuator.

My 2000 GMC had a regular cable that actuated the TB plate, so it was easy for me to just use my hand to move the throttle plate wide open while I sprayed the 3M throttle body cleaner. Taking off the IAC (Idle Air Control) motor was a bit more complicated, and the GM shop manual had plenty of cautions and warnings about not trying to move the IAC pintle valve by hand, or risk ruining it.

It was a giant PITA going through the Idle Learn Procedure, which GM requires if you happen to remove the IAC motor on that year truck. At least I didn't need a scantool, it's a drawn out procedure but can be done in the driveway. I'm hoping a Prius isn't more complicated to clean out the TB and intake manifold.

<div class='quotetop'>QUOTE(conversion02 @ Feb 19 2007, 11:27 PM) [snapback]393083[/snapback]</div>

The Prius airfilter box sits right over top of the TB assembly. I haven't noticed a MAF used on the Prius, I used to have a 1990 Toyota 4Runner so I'm very familiar with how a MAF looks like.

In Winnipeg city driving I can usually get 16,000 km out of an engine air filter, though usually less in summer. Lot's of PM in the air from all the diesel busses, super duty turbodiesel pickups, and stinky VW tdi cars. In summer the home construction stirs up a lot of dust, especially if dry out.

 

<div class='quotetop'>QUOTE(conversion02 @ Feb 19 2007, 11:27 PM) [snapback]393083[/snapback]</div>

I stand corrected. This got my curiosity so I went down into the parking garage to check out the Prius airbox. I'm used to vane style MAF, like the kind used on my 1990 Toyota 4Runner V6. This one is different.

At least it appears clean ...

 

Do you use Toyota (paper element) engine air filter?

I ruined my MAF sensor in my 00 Celica after using TRD (K&N) oil based filter. It was soaked out of the box and I did not add extra oil to it. Anyway, I am staying away from K&N for my Prius.

Dennis

 

<div class='quotetop'>QUOTE(usbseawolf2000 @ Feb 20 2007, 10:49 PM) [snapback]393644[/snapback]</div>

Yes, I also have a concern about oil carry-over with K&N or any similar oiled element. I used a Downey kit on my 1990 4Runner V6, and even being careful the vane MAF meter was gunked up by 1998. However it was fairly easy for me to take it off and clean it.

As far as filtering efficiency, I'm still unconvinced the K&N is better. On the tractor at my hobby farm, I have an oil bath pre-filter, than a primary paper element filter. That combination really does work.

I used the Donwey kit in my 1990 4Runner primarily for better power, the stock airbox was terribly restrictive.

 

<div class='quotetop'>QUOTE(nwprius @ Feb 15 2007, 06:40 PM) [snapback]391229[/snapback]</div>

You sure you converted to US gallons instead of Imperial gallons? Imperial gallons are larger. That sounds high for 80 mph.

As for gasoline with or w/o ethanol, we seem to have no choice in California. According to http://www.energy.ca.gov/gasoline/types_of_gasoline.html, ours "usually contains 5.7% ethanol as an oxygenate or in a few areas may contain no oxygenate (CARB RFG Non Oxy)."


<div class='quotetop'>QUOTE(DFWPrius @ Feb 16 2007, 07:02 AM) [snapback]391415[/snapback]</div>

I've NEVER heard that air filters should be changed at the same time oil and oil filters are changed on ANY car's maintenance schedule. Another guy mentioned he changes it every 3K on his Tbird and 5K on his Prius. That sounds excessive.

In the Prius maintenance book, it calls for air filter replacement at 30K miles or 36 months. It also says to inspect it every 5K miles if driving in desert or dirt roads.