Mazda5 real-world Mileage numbers

[RnDM5]

Wow, thats good milage compared to what I have experienced. In my case I wonder if the fuel was contaminated or something. Funny thing is though is that the 5 ran smoothly the whole time making me think that fuel contamination and engine are fine.

 

[flcruising]

I don't see how you can get such bad highway mpg without seeing black smoke trail behind you!?

We went on an all interstate trip to Texas 2 months ago (1600 miles round trip). Had a HUGE cargo carrier on top. Used gascubby the whole way. Averaged 26mpg. This is acceptable to me. Not great. But our last vehicle was an '00 S10 Blazer 4X4 that was lucky to get 20 mpg highway. My dd is an '00 Mitsubishi sedan automatic that I can't get less than 30 mpg in.

 

[mpvue]

That all being said I was excited to go on a short road trip with my wife this past weekend both to get away from the kids and to see what the hwy mpg would be. On cruise control at 75 mph (120km/h) with 2 stops for construction I got 16.4 MPG (14.3L/100km)!!!!! I get the same if not better mpg with my brick of a '01 Xterra!

I think you need to get some more data points before you assume something is wrong. when I did a LONG road trip last year (pennsylvania to louisiana) I plotted every fill up; most were 27-29, but one was like 19 and another was 31. I attributed the low one to early pump shutoff.
now, the 5 is our only vehicle, so between my commuting and my wife running errands, we get a consistant combined mpg of 23. I now know I can go about 260miles on a tank and its time to fill up.

 

[RnDM5]

You may be right, however the software I use doesn't rely on a FULL tank. I enter the amount purchased and then the distance travelled and i get my mpg since last purchase/recording. I could only put $10 in and it would still give an accurate mpg.

I'm not sure why the 5 was so thirsty on that trip but plan on monitoring things closely before spending $$$ to get it looked at. I may have to find a reason for another road trip! ;-)

 

[Rockin03mp5]

sounds like some funny math to me. somewhere, something is wrong there. ive never gotten less than 20mpg. i actually think my worst is 23.

 

[twintrbo]

That is really bad, I should know! I think I get the worst numbers here and you even have me beat. My worst tanks have been around 16 MPG in pure city hell, during the summer with full time A/C. The one real highway trip I took, I got over 28 MPG and that was with some rural slower back roads and 2 lane backups to get through some towns. I dont know how you did so poorly on the highway, there would have to be something really wrong with your 5 and I doubt you would not notice it. I think something got computed wrong, I dont see any other way it could be possible.

Had to ask, you did have it in 5th right? Running it in 3rd instead of 5th might do that. Sorry to even suggest it but I'm out of ideas

 

[RnDM5]

It was definately in 5th while cruising as the rpms were only 2700. I question whether its a math error as when I filled it, I reset the tripmeter and made note that the fuel guage needle was above the Full mark. I realized how quickly I was going through fuel when I had travelled about 60 mi/100km and had used just over 1/3 of a tank! Crazy.

I now wonder if the fuel float (for the fuel guage), they still use those don't they, in the tank may have been stuck falsely high.

I have driven to work the last few days and consumption seems to be back to normal but then again it always has been on my work commute. I think the only way to reassess is to drive the same 2 hr route and see what happens.

 

[twintrbo]

Someone in one of the threads was convinced that if the tank was filled up with the car off-level, it would not top off properly and therefore mess with mileage calculations. I would say it is possible. I noted my last tank did almost 40 miles before the gauge began to drop from Full. Since the 5 has a fairly small tank, there can be a big difference if you miss a couple of gallons.

Example:
13 gallons for 260 miles = 20 MPG
11 gallons for 260 miles = 23.63 MPG

Almost 4 MPG would bring you from 16 to 20, still terrible but it would at least account for some of it.

Wait a sec, how can the software be accurate if you dont know how much fuel you used? If you put in 13 gallons and filled up after going 100 miles, how would you be able to figure your MPG?

 

[thaxman]

Still getting 22+ city toting a carful of kids around everywhere and stopping at stoplights every 1/2 mile. Drops to about 19.5 in the summer w/full A/C and 110 degree days, but that is better than any other car I have had before, too, except the 1.5L CRX 5MT, which got 29 under the same circumstances.

But we don't talk about hwy mpgs tho w/avg Interstate speeds being 80 mph+

 

[switz]

You may be right, however the software I use doesn't rely on a FULL tank. I enter the amount purchased and then the distance travelled and i get my mpg since last purchase/recording. I could only put $10 in and it would still give an accurate mpg.

I'm not sure why the 5 was so thirsty on that trip but plan on monitoring things closely before spending $$$ to get it looked at. I may have to find a reason for another road trip! ;-)

As a math teacher, the only way to accurately measure the fuel economy is to fill it up to exactly the same point every time and record the distance travelled. If the tank wasn't full when you started recording your trip, how can you fill it up to that same "not full" point after your trip to determine the exact amount of fuel used to go that distance. If your tank really wasn't full when you started recording your distance and filled it right up after your trip, you not only filled up the fuel required for your trip but the fuel you used covering what-ever distance it took to get your tank to the original "not full" point. This would make it look like way more fuel was used and your economy would be way down.

That said, it is much better to average economy over many fill-ups because you can never fill the tank up to the same point every time (unless you fill it right up to the filler opening each time). My average over a long period of time is anywhere from 24-32 imp mi/gal.

Hope this helps

 

[RnDM5]

Hey guys, I hear what your are saying. I always fill to the auto shut-off of the gas pump at the same gas station and even the same pump. The car is always level, at least level enough to not affect filling. The exception here is that on our trip I filled at a different station than usual before heading out. I assume from all that you have said that this may be the source of my problems. Time will tell and so will the next road trip.

Oh, I do average my mpg over all fill-ups and am currently sitting at 22.2 mpg combined hwy/city. Not too bad but not as good as some of you.

Thanks again for all your thoughts and that next time I road trip I will post an update.

 

[switz]

So today when I filled up I thought I'd see how much of a difference it would make if I filled up only stopping when the nozzle shut off. I had gone 583km since the last fill up. The pump shut off after 49L. That's 33.6mpg (imp) or 8.4L/100km. That sounds really good But I kept adding until the fuel was right up to the neck of the fill tube. 59.2L (pretty good for a vehicle that only has a 60L tank and the yellow 'add fuel now' light had just come on with the needle still above the "E"). That works out to 27.8mpg (imp) or 10.2L/100km. That doesn't quite sound so good. Last time I filled it I added a couple of litres past the shut off point but I didn't spend the time to fill it right up to the neck so my actual economy for this tank was probably somewhere around 9-9.3L/100km. Unless you fill exactly the same way at the same station using the same pump, the errors introduced can be pretty large.

Hope this helps. By the way this tank was a day-trip from Lloyd to Edmonton and back. Temperature was -8C going in the morning and -16C on the way back around midnight. I set the cruise at 110km/h and was loaded with five passengers, a bunch of Christmas presents aboard and the Thule up top on the roof rack.

 

[flcruising]

I always try and 'top off' my tank when refueling at the same pump. This gives you the most accurate mpg results. Unless you intend on weighing how much fuel you consume, you can't get much closer than consistently using the same pump.

If we all were really that concerned about fuel economy, we'd all drive around like senior citizens. It's really less about knowing the information, but applying it. What good is it really to check your mpg every time unless you are consistently adjusting your driving technique to maximize it? I can only do so much mpg-wise in the 5 since the wife is the one who drives it. I just have to pay the fuel bill. (wink)

 

[twintrbo]

But I kept adding until the fuel was right up to the neck of the fill tube.

Just so you know, thats not recommended for many reasons. It can harm the vehicle and thats why there is an auto shut off on the pumps.
http://ask.cars.com/2007/07/gas-top-off.html
http://www.epa.gov/donttopoff/

 

[flcruising]

I've never had an issue topping off any fuel tank. The charcoal canister is installed below the top of the tank in the 5, so I'm sure the PCM doesn't purge unless it knows it's safe to.

 

[twintrbo]

I've never had an issue topping off any fuel tank. The charcoal canister is installed below the top of the tank in the 5, so I'm sure the PCM doesn't purge unless it knows it's safe to.

You are giving them too much credit You can do whatever you like, of course, I'm just pointing out some information you might not have been aware of. Although I will ask you this: If you put 70 degree gas from underground storage tanks into your car on a 110 degree day and fill it to the cap, where does the fuel go from the liquid expanding?

 

[flcruising]

Simple. The fuel expansion is nill, it's the vapor where the concern is. The gas cap is a pressure release, but I doubt there's much problem here because...

I do "No-no" #2 almost every time I fill up - I leave my engine running. When I stop for fuel, it's always after work, the gas station I use is 1 mile away. I'm more concerned about warming the engine up before heading on my way home. So, when I have to stop for gas and the temp gauge has barely moved, I leave it running.

I say this to tell you that when I 'top off', even when the engine is idling, the fuel drains down rather rapidly from the filler neck. It travels down out of sight below the splash valve within seconds. Another thing, the rate of evaporation is relative to exposed surface area of the fuel and the volume that it can expand into. When the tank is full and travels up the filler neck, there's very little exposed fuel surface area, so the vapor is minimal.

 

[twintrbo]

So, when I have to stop for gas and the temp gauge has barely moved, I leave it running.

I say this to tell you that when I 'top off', even when the engine is idling, the fuel drains down rather rapidly from the filler neck.

So that's no-no #3 and its a good thing you're not OCD or you wouldn't leave the station lol

I am surprised you would ignore warnings from reputable sources. Even if you havent experienced any mechanical issues, its still considered a non eco friendly move and there is no guarantee it wont cause problems in the future. Nothing is broken, until it breaks, you know! To each his own of course, I hope nothing does go wrong for you.

 

[mpvue]

Simple. The fuel expansion is nill, it's the vapor where the concern is. The gas cap is a pressure release, but I doubt there's much problem here because...

I do "No-no" #2 almost every time I fill up - I leave my engine running. When I stop for fuel, it's always after work, the gas station I use is 1 mile away. I'm more concerned about warming the engine up before heading on my way home. So, when I have to stop for gas and the temp gauge has barely moved, I leave it running.

I say this to tell you that when I 'top off', even when the engine is idling, the fuel drains down rather rapidly from the filler neck. It travels down out of sight below the splash valve within seconds. Another thing, the rate of evaporation is relative to exposed surface area of the fuel and the volume that it can expand into. When the tank is full and travels up the filler neck, there's very little exposed fuel surface area, so the vapor is minimal.

that has got to be THE most in depth analysis of the 'science' of putting gas in your car. seriously, dude, get a hobby.

I go to the same gas station almost all the time, they pump it for me (the law in NJ) and my mileage is always around the same. all that crap about temp expansion, different auto shut offs, etc, is a waste of time.

just put the gas in and go.

 

[Rockin03mp5]

new jersey...

something must be wrong there if they have a law saying you cannot pump your own gas.

i dont watch the jersey shore for a reason.

lol

(this post was not meant to offend anyone... except people from new jersey... who fit the stereotype)