Bad mileage myth?

You might make plenty of short trips, but a far greater percentage of your tank is very long trips.

As near as I can tell, the Prius must spew uncombusted gasoline out the tail pipe when it's warming up, because the milage during that time is really, really bad. For me, it's typically 35 MPG in the summer for the first 5 minutes and 25 MPG in the winter for the first 5 minutes.

So, I think it's well established that during warmup, the engine's efficiency really sucks. Now let's examine that "I make plenty of short trips with a cold engine" comment.

My wife and I each have a Prius. I've been getting 48 MPG or so for the last couple of weeks and my wife is getting 35 MPG. When it was colder, I was getting 43 and she was getting 30.

Now lets compare her drive and my drive. I commute 16 miles for about a 30 minute commute. On the weekend, I might make 3 or 4 short trips of less than 10 minutes. So, monday through friday, I spend 5 minutes getting bad gas milage and 25 minutes of really good gas milage for each leg of my commute. So, during the week, I spend 50 minutes getting bad gas milage and 250 minutes getting really good gas milage. On the weekend, my 4 or so trips of less than 10 minutes contributes an additional 20 minutes of poor gas milage and 20 minutes of good gas milage, resulting in a one week total of 70 minutes of really sucky gas milage and 270 minutes of really good gas milage.

Therefore, for my driving, I'm getting good gas milage for approximately 80% of my driving.

Now lets look at my wife's driving. She is a stay-at-home mom and primarily goes to gym, drops my daughter off at kindergarten, and goes to local stores. Most of her trips are 7 minutes or less, and many are less than 5. I'm not going to try to do the math, but it should be obvious that for her driving patterns, instead of driving 80% of the time with a warmed up engine getting good gas milage, she is probably driving closer to 80% of the time on a cold engine getting bad gas milage.

Now you, with your 120 mile commute, even with local trips in the evening or on the weekend, are probably driving approximately 90% of the time with a warmed up engine getting good gas milage. That's why you get good gas milage without even trying and why other people can't get good gas milage no matter what they do.

I would bet that if everyone accurately estimated the percentage of time they drive with a cold engine and the percentage of the time they drive with a warm engine and then used the following formula, they would come close to their real world milage.

Pcold * 60 + Pwarm * 35 = mpg (for summer temps)

Pcold * 50 + Pwarm * 25 = mpg (for winter temps)

Where Pcold and Pwarm are between 0.0 and 1.0. (80% = 0.8)

 

Outside temps matter (~5 mpg at in low 20's F, vs > 50F), but engine temp matters a whole lot more. I drive many jaunts of 10 miles in 25 - 35F weather through the winter, usually with 2 - 5 hour intervals when the car gets to cool off. IF I wait to turn on heating for 5 minutes, and only use it on uphills or accelerating, my FE is about 55 - 60 mpg at night with no traffic to speak of in suburban/city driving. For comparison, if I use AC with abandon, mpg is in the 40's (I know from my wife's habits), vs 65 - 70 mpg in ideal weather.

 

well 40 pound ca18kg right ?) in total isnt that bad is it ?
I Guess there is many factors that will affect how much more gas your car will use when putting on heavier weels,, and that would affect more in acceleration gas usage and performance , when ure in desired speed it shouldnt affect the gas/milage that much.
And i theory you sould get alittle more back in power to the batteries when ure deacceleration ( "flywheel " effect should affect both ways.....)
It also depends where in the weel You have the new 10 pound weight , distributed allover in same pattern as the original weels or ?? and so on..
my experince is that the tire itself plays a big role in gas milage. the pattern of the tire, profile bla bla

i might be utterly wrong ,
aslong it looks good on the car and not made of lead ..... im happy

*Andreas

 

all in all, i have to agree with the Doc. the whole basis of this thread is not understanding how people can get very low mileage. sure there are extremes. the first winter i had my car, i was in a training class that was 1.1 miles away from my front door. it lasted 6 weeks. we had 60-90 minutes for lunch, most of which i spent at home, on the computer, here at Priuschat (bet that was a shocker to you!!) so that was nothing BUT short trips. and my mileage was in the mid 30's. but a few trips of 70-80 miles on the weekend was enough to bring me back to the low 40's.

back when i only had 3000 miles on my car, i helped a friend deliver the morning paper. that was over 160 stop and go deliveries. only did 4 days worth but during that time (i did fill up the night before i started the 4 day run) i averaged 41 mpg. granted it was summer time, but this is WA State and at 3:30 in the morning, it aint that warm no matter what time of year it is.

but there have been a lot of people who have 20-30 mile commutes on the freeway or some variation of, claim to drive very conservatively and still get mileage in the 30's. i have to side with DocViJay. i simply dont see how it could be done without driving like a maniac.

 

Recipe for 29 mpg:

Park your Prius in an unheated garage when the outside temperature is 30 degrees below zero Farenheit. Start the engine and turn the heat on full to pre-heat the cab for 5 minutes before driving, because at 30 below zero your fingers would freeze and break off. Drive 4 miles in 10 minutes without the car ever getting into Stage 4 operation, and with the heater on full blast all the way, so the engine never shuts off. Park the car. Jog at the YMCA. Start up the car and drive 2 or 3 minutes to the office, and park again. In the afternoon, when the temperature has warmed up to a tolerable ten degrees below zero, drive back home, again with the heater on full blast, though this time without a pre-heat. Don't use the EV switch because you didn't have one that first winter when the car was new. But do accelerate hard because you are in a hurry to get back into a heated building.

And, no, you would not like riding along. It's too confounded cold. Which is why I don't live there any more. 29 mph is not too hard to achieve. Here in Spokane I'm getting 50 mpg and satisfied with that. Fargo's a nice place, but you have to be half polar bear to survive the climate.

 

OK Daniel. Good point. I've heard you and other like Jayman mention those conditions. That makes sense, no arguments here. However, it seems that people in much milder climes have experienced similar results. That's who I'd like to ride along with (no offense )

 

No offense taken. But has anyone actually gone below 30 mpg without bitterly-cold weather, or a one-mile commute? Take a look at your first 5-minute segment, and consider the person whose daily drive is 5 minutes.

 

Who are the people in Florida & California getting 30MPG? Are they on PriusChat?

 

Last week I went to the dealership for a "new Toyota owners night". The interesting part was when they divided us into Prius and non-Prius groups for a shop tour. There were about 8 Prius owners and a couple who owned a Highlander hybrid that attached themselves to our group. Our "guide" was described as the sevice department's " master diagnostician". The Highlander couple kept bitching on how they weren't getting the EPA mileage and how unhappy they were about it. They were a couple of a--holes who wouldn't give our guide a break or even respond to questions about tire pressure, driving habits, etc.

After they stormed off, the guide told us about a mileage problem he had with a Prius a few weeks ago. Angry call - owner was only getting 12 MPG! After the usual fighting back and forth with the various layers of the service department, it landed in the "master diagnostician's" lap. He asked the person to bring the car in. When they did, he went out with them to look at the car and as he approached it the engine came on. It turned out that the owners thought that was how it should operate. They had not listened to the sales guy at delivery or bothered to read the manual. The car had been on since they picked it up. They had been through several tanks of gas and had been keeping it in their garage (thank God for low CO emissions?). Our guide explained the Power Button, demonstrated it, reset the consumption screen, and sent them on their way.

So that's one way to get 12 MPG. I got the impression from questions that I was the only one there that night that had read the car's manual (Prius owners or not).

- Tom

 

Daniel:

Been There, Still Doing That.

The winter front and Mobil 1 0W-20 made a *huge* difference this winter. We were unusually warm most of the winter, but in Feb had enough -30 to -35 C weather to make up for it. I never got worse than 6.8 l/100km tank average, ccompared to 9.8 l/100km last winter.

Of course, a Prius that is getting "only" 9.8 l/100km is still getting *way* better than every other car around it. My co-worker with the '04 Golf TDI actually gets 10% worse than I do in winter driving, and he has to put up with a diesel in very cold weather.

As far as the effect of tires, I noticed when I took off my Michelin Harmony on the OEM wheels, and put on the Yokohama Ice Guard on steel wheels, my tank average went from 4.8 l/100km to 5.1 l/100km.

jay

 

I gotta say that, for all of Spokane's disadvantages (bigger city than Fargo, not as friendly) I am really happy to not have those bitterly-cold winters. About half-way through my present tank, the tank average is 51 mpg. Of course, part of that is, being a bigger city, I have to drive farther, which I don't like. But I was never made for severe winters.

One thing I've noticed is a mileage killer is making a lot of stops: After every stop the car seems to burn a bunch of gas right away. Someone who makes a lot of very short trips with multiple stops is going to get worse mileage than someone who has a long drive without stops. At least that's how it seems to me.

 

the stops are always a killer. too much kinetic energy lost and regen recaptures like what??? 3-5% i think i heard somewhere. not very good...

 

Well, I'm perplexed. Normally we are getting about 41 mpg right now. Granted that is mostly short trip driving, but even when I have gone on longer ones, it is rarely over 45. We have high pressure in the tires, and practice pulse and glide techniques. I'm not complaining, it's still cool out and short trips are hard on fuel economy. This is double the mileage of our old Subaru or the Honda Odyssey under the same circumstances.

However, last night I stayed a little too long at a friends and had to really hustle to make the ferry. I had filled the tank just before stopping at my friends. With only 20 min. to get to the boat, I dashed out, jumped in the car and hustled to make it. At times I was up to 75 mph, hills and fuel economy be damned, I was on a mission and made the boat, phew! Took a deep breath and then looked at the fuel consumption. It registered 54.5 mpg with outside temp 46 degrees! This trip was about 9 miles, 70% hwy and 30% local streets. Now I'm perplexed. I broke most rules, quick off from the lights, gunned it on hills, but got great mileage. Wazzup?

PS: I learned a little about the car's handling too, but that's another thread. I really want to get the BT plate installed now.

 

We had a long trip with our Prius last week end, and I am very satisfied with the MPG. We averaged 57 MPG over a 9 hour drive, and it was freezing cold as well - so that the ICE was partly on sometimes just to give heat to the A/C.

I expect to get closer to 60 towards summer!