Suddenly poor gas mileage

I just bought 2013 Prius 3. My drive is 15 miles, weather is in 80's and 90's. The traffic on the road is heavy.

The car is 2 weeks old and I am only getting 37mpg.

 

You should take your car out on the weekend when traffic is less congested and check your MPG again. My son used my Prius to practice parallel parking for an hour, I got 8mpg.

 

Please use Google Map to chart your path from your neighborhood to work. Then post the URL. Alternatively, use Google Earth and plot your route and post the ".kml" file. We can then explain what is going on. We don't need your home address, the nearest intersection is enough.

You have figured out how to 'reset' your trip meters, right?

This is the first tank?

Bob Wilson

 

I've noticed similar performance with mine.

AM commute involves maybe a few miles of congestion where I am "crawling" before it opens up again. Other than that I am going 65-70 nearly the whole way. Computer readout for the trip for those so far has been 52-55. It is about 40 miles that I cover in 46 minutes or so. It has been about 70 degrees at that time recently.

PM commute often involves some gridlock, some 65 mph highway driving, and "ghost" traffic jams where I get to slam on my brakes and come nearly to a stop for what appeared to be absolutely no reason at all. Those trips end up being 46 miles (slightly different route), take 1-1.5 hours, in 95 degree heat recently, and I'm looking at a range of 44-49.

Around town the numbers struggle. I took a trip to the dry cleaner last night on a parkway with 45 mph speed limit and stop lights. Maybe a 10 minute trip and the computer said 31. Today I went to Costco on a similar route and got 37 on the computer. I just think the 35-45...complete stop...35-45 routine really kills the mpg. I imagine the 51 mpg "city" rating is at a lower average speed, so less accelerating from a stop.

 

I have a 2012. I went from a 27.4mile highway commute down to a 5 mile city commute. Mileage went from an average of 47-48 down to just over 40.

 

It turns out the first 1-2 miles is at ~30 MPG due to warm-up:

30*2 + N*25 = 48 * 27 :: N~=49 MPG​

30*2 + N*3 = 40 * 5 :: N ~= 47 MPG​

Solve for N, after warm-up, you are getting between 47-49 MPG​

To make a significant improvement in your MPG, you'll need to consider ways to mitigate the warm-up cost:

• block and transmission heaters - can bring the coolant temperature up saving about 2 minutes, ~1 mile of warm-up
• test 'let engine run to shutdown in first drive of day' - alternate days with either starting the car and waiting for the engine to stop versus driving off in the morning. Use a trip meter for at least three or more samples each.
• test 'use 25 mph neighborhood speeds first mile' - change your route to minimize speed in the first 1-2 miles to 25 mph using "N" to coast as much as possible

Short trips like these are perfect for plug-in vehicles, either Prius or others. Personally, I like the Prius because it has superior highway mileage BUT I don't own nor am shopping for a plug-in.

Bob Wilson

​

 

I have a 2010 Prius IV delivered in July 2009 under the Cash For Clunkers Program. Best deal I ever made. Traded a 1994 JAGUAR XJ6 with 224,000 miles. Barely made it to the dealer. Mileage was great until about 35-45,000 and then it turned to pucky. MPG went from 42/50 mpg city highway to 30/45 city highway. Dealer seemed to have a "standard line" intimating that tire replacement was at fault with Michelin Tires "which are heavier than Avid 'hybrid' tires." However, my stock aluminum rims weighing in at 20 lbs each were replaced with lighter weight rims made by Motegi Racing SP 10, only 14 lbs. Six pounds lighter than stock aluminum rims at 7,000 miles so 24 lbs of rotational weight saved. I am also in Southern California where no cold temperature issues are encountered.

So Toyota Dealer Service Management claims that it's the difference in weight between the OEM tires and Michelin Defender replacements. I guarantee you that the difference in rim weight was far greater from stock to after market. The Toyota dealer response sounds disingenuous; like a scam perpetrated by management and I can't get a straight answer out of any service manager. It seems like the same answer each time without regard to anything specific, just unfounded assertions that a heavier tire could be to blame. These answers the service writers give are ones which none of my automotive engineer friends seem to think are plausible.

When fuel economy drops so precipitously and suddenly, why rush to blame what the consumer did? Doesn't that imply a bias? If the decline in fuel economy is due to the engine wearing in with age, then just say so! But don't represent that the Prius can get 45/50 MPG city/highway when it won't achieve that long term just to sell cars!!! It's fraudulent. Be honest.

Toyota is giving a BS answer to a critical question about advertised fuel economy, which is not achieved after the wearing in period is completed within 40,000 miles. All service was performed by Certified Toyota Prius Mechanics at an independent dealer. No codes appeared during the diagnostic tests under my extended warranty. I love the functionality of the car, the turning circle, but not the road noise nor the fuel economy.

Does anyone else have this problem in normal climate with a 2010 Gen 3 Prius with more than 30,000 miles on their engine? I have 60,000+ miles now ending my 5th year of ownership.

 

There can be problems with older Prius that are difficult to diagnose. But first we must know the Prius is actually broke. It helps to have a benchmark to compare with the current MPG. The key is to repeat the benchmark at two speeds on either side of 42 mph. Above 42 mph to check the engine and below 42 mph to check the hybrid system:

The protocol is:

• find a 10 mile, level stretch where the car can run on cruise control
• warm-up the car for 15-20 minutes
• enter the 10 mile stretch at the target speed
  • set the cruise control
  • reset the tripmeter
  • drive 10 miles and take a photo of the tripmeter with MPG and speed
• repeat in the opposite direction
• average the MPG and speed numbers

This test also separates complainers from those who want an efficient Prius.

Bob Wilson

 

Very interesting Bob. It's a bit difficult to find a 10 mile level stretch where I can go 42 mph around here without going 40-50 miles out of town. Maybe on the freeway in the middle of the night, but even that's tough. But I'll give it a shot. Why 42 mph? What's your background?

So you have one Gen II and one Gen III?

There seems to be a lot of mileage complaints. I realize that short trips and rapid acceleration will cause mileage to suffer as well as running the A/C, but the reasons the dealer gives seem unfounded.

What does 52 MPG - NHW11 (100k mi / 155k mi total) and 52 MPG - ZVW30 (42k mi / 42k mi total) mean?
Particularly NHW11 and ZVW30?

Thanks for your help and feedback.

George

 

Excellent! I have done a lot of mph vs MPG tests at 2:00 AM when I knew traffic and wind effects would be minimal. Being in the Bible Belt, dawn Sunday morning to about 9:00 AM is good.

Our Prius have two modes whose boundary is 42 mph. Above 42 mph, the engine runs all the time although based upon the load, the engine can in effect 'loaf along' with very low rpm. It is the same as going down hill and holding the clutch so the engine runs at idle rpm.

Below 42 mph, the car runs in 'hybrid mode' which means it flips between engine running powering both the car and putting charge on the battery and times when the engine is off and extra battery energy keeps the car rolling at speed.

This is more of an executive summary versus some of the more obscure areas of Prius performance I and the Prius pioneers at 'Prius Technical Stuff' have looked at some very obscure areas. Still, feel free to ask and if I don't know, I'll point you to someone who does.

I studied mechanical engineering until a low draft number and failed relationship led me to spend four years in the US Marines (aka., the USA version of the Foreign Legion.) But everything got better after I left the Marines.

Once I got out of the Marines, I went from computer operator to operating system programmer and then 13 years with General Electric where I learned applied engineering. I left GE to work for Boeing at different NASA centers and now work for SAIC at Marshall Space Flight Center.

I'm an engineer because when I was about 3 or 4 years old, I saw a steam engine and asked 'who is that man?' and was told 'he is the engineer.' So I became an engineer only because they didn't say,'the driver.' <grins>

There has been a little bit of a 'holy war' about what we've got:

• 2003 Prius - NHW11 model (although one Wiki jerk calls it something else), Gen I here (although the first Prius is a Japanese-only model, the NHW10, never sold here.) It is the same as the 1.5L, compact, sedan.
• 2010 Prius - ZVW30 model (although the same Wiki jerk calls it something else), Gen III here. It is the 1.8L, hatchback using the modified Highlander transaxle and newer modules.

I'm sanguine about 'a rose by any other name' would still get 52 MPG!

One of the early lessons learned is how technically shallow are many of the dealer teams. Without going into a lot of history, the rule is the smart ones find better jobs. Dealer service departments are pretty low in the technology totem pole and I DON'T FAULT them. For many, it is an entry job. The smart ones get a better job . . . quickly.

Opps, I need to update my signature:

• 2003 Prius -> NHW11, currently has 165,000 miles. Bought used with 49,300 miles, I bought it in Fort Worth and drove it to Huntsville. Today it is my work commuter car filling the same role as a 'Prius c' but with a few experiments.
  
• 2010 Prius -> ZVW30, currently has 55,000 miles. Bought new for my wife, it is the one I drive her around and take on cross country trips. It gets 52 MPG about 5 mph faster than the 2003 Prius.

No problem. The current model Prius brought one piece of engine technology that still has my attention . . . the cooled exhaust recirculation (EGR.) What bothers me is the long-term prospects. First some background.

There is a 5th pipe on the exhaust manifold that passes forward through a coolant, cooled channel and into the intake manifold. A valve controls how much exhaust gas feeds in to dilute the air that mixes with the fuel. Because the exhaust has no oxygen, it cools the flame but it is primarily used at high power settings. At high power, the exhaust can be so hot that it burns out the catalytic converter (and ages the exhaust valves and seats!)

In the earlier 1.5L Prius, 2001-03, and 2004-09, Toyota uses 'fuel enrichment' to reduce the exhaust temperature. So if you can keep the engine power demand out of that super-rich mixture region, you can get excellent mileage. But if you 'tickle the tiger,' the fuel economy will go into the toilet, especially with the 2001-03 model.

In contrast, the current Prius engines add cooled, exhaust gas to the intake air charge at high power settings. This keeps the exhaust temperatures low enough that fuel enrichment is not needed. So the current model Prius can continue to run a lean mixture without burning the valves and catalytic converter. But that is not what bothers me.

Count the number of pipes on the exhaust manifold and notice one of them, the lower one, feeds back to the engine:


The exhaust is taken out before the catalytic converter. This means it is often cycling between lean and rich that is needed to operate the catalytic converter. But rich means it likes to deposit carbon on any surface cooler than that hot exhaust. This is not a problem with the catalytic converter because during the lean, it traps the oxidizing NOx compounds and in effect 'burns off' the hydrocarbons in the rich cycle. But the cooling heat exchanger and valve is not made out of catalytic converter material. I am concerned that like the old "heat riser tubes" found in 1970s cars, it can 'coke up' with carbon and stop working.


Well if the cooled exhaust can not reach the intake manifold, the engine controller has no choice but to use 'fuel enrichment' to keep the exhaust gas temperatures within reason. But does it 'throw a code?'

I won't feel good about the EGR mechanism until someone disassembles a high-mileage, short-range, urban Prius and inspects the EGR heat exchanger and valve. If they have the same light coating we find on the inside of the tail pipe, there is no problem. But my engineering sense suggests this is an area that needs checking. There are pathological modes where the EGR would be at risk. But I've wander off into the weeds.

We really need to have some benchmarks run with your Prius to see if there is an obvious problem. If there is a Prius problem, we'll work with you to diagnose and debug what is going on. The problems you see may affect others (including me someday!) So we have a lot tools to apply to this problem BUT we first need to find out if it is a problem we can demonstrate against the benchmark.

Bob Wilson

ps. You might like: Detroit Auto Show and Prius 2010

 

LOL, if not the fact that the OP started the thread in 2011, it would be universally blamed on the "recall".

 

To answer: my 2010 Prius 2 gets the same fantastic mileage as when new. It has 63000 miles on it with the original Yokahama Avids still on it with about 10 or 15 K left. Unfortunately I picked up a nail too close to the sidewall so I will now replace the whole set. I never installed the plastic wheel covers to save weight.

 

how much weight does that save?

 

Bob,

I can't imagine that you haven't seen this thread, but I'm curious if the following is consistent with your theories about the EGR gunking up:

Prius III engine knocking at high torque low RPM (solved) | PriusChat

Thanks! Your insights on Priuschat are always interesting to me...

 

Thanks for the link. Sad to say it sounds like the blocking plate was 3d party installed and then had a failure. I can not use that as an example. We really need original configuration examples. However, the carbon deposits are exactly what I fear.

Bob Wilson

 

I would have to go back through the thread but I thought there were other people that chimed in later and claimed they found similar buildup.

HTC One M8

 

If your car is a 2010 or newer Toyota says to use 0w20 synthetic oil. It even has 0w20 printed on the oil filler cap.

 

I posted a thread awhile back whining about my gas mileage only being around 37 or so...well I am learning how to drive the prius and I'm up to around 43. I can live with that even though others say that's low. My heavy 17" aftermarket wheel setup ain't helping, but it's a trade off

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