Real Bad Gas Mileage!

[singlemalt_18]

The Gas Guzzler and the Bartender

Seeing that this is an issue that won't seem to go away, I am beginning to think that the reason for most of the 12 mpg experiences comes down to the individual driver. The current EPA ratings, and misleading marketing have have certainly contributed to the frustration, but I can only conclude that the performance characteristics of the 4 cylinder DISI turbo engine must be to blame.

There is no question, that when called upon to produce power, IT DELIVERS !!!

But does it do so with a reckless abandon of sorts?

I am 47 years old, and I have never gotten less than 17 mpg in the 4700 miles logged on my AWD GT; I average about 18.5 mpg. Last week however, my wife & I were moving some of my office stuff, and we had the CX loaded down with more than I imagined we would be able to fit; it was at least an additional 500 to 600 pounds. To my delight, the CX-7 did not seem to loose an ounce of spunk! To my chagrin, the gas guage appeared to be in free fall.

Imagine for moment, that you have two big bottles of Jack Daniels, two shot glasses, and a bucket. Take one bottle of JD, open it, and pour a shot of the bourbon into one of the shot glasses. That is easy.

Take the other bottle of JD, and empty it into the bucket. Now pour a shot of bourbon into the other shot glass from the bucket... do you think you may have spilled a little bourbon? (And this assumes you did not consume any of the bourbon first!)

Take it a step further. Imagine you now need to fill a bucket with bourbon as fast as possible. Would it be quicker to fill the bucket from a bottle of bourbon, or fill the bucket from another bucket?

At my age, I KNOW I have become a much more conservative driver than I was 20 or even 10 years ago. There is no avoiding it - it just happens. I think the engine is capable of delivering bourbon by the bucket, and most of the time, all any of us want is a shot.

Please forgive my analogy, but at my age, I'm more concerned with spilling a drop of 18 year old scotch, than I am about burning a little extra gasoline. Its much more expensive!

Any thoughts...?

 

[mikey1981]

my thought is people cant seem to get over what it says on the window sticker and enter into reality.

 

[CXRabbit]

I think part of it the the window sticker.
I think part of it is people out there reporting they are getting 24+ MPG without knowing if they're even calculating properly.
I think part of it is how you drive.
I think part of it is where you live (different mix of gas).
I think part of it is climate (cold weather warm-ups and idling).

For me, part of it is the plummet I've experienced. First few tanks I got around 14 MPG. Totally expected it. Next four tanks were 16.54, 15.46, 18.18 and 17.23. Again, totally expected results. But now my last two tanks have been 14.79 and 13.12! A big surprised (or wake-up call, LOL). I've been doing more around-town driving and a lot of warming up the car longer (because of cold weather) both of which kill mileage.

Over the long haul, I do hope it average out a little higher (my average now is 15.45 MPG)... but if it doesn't, that's the price I pay for buying an SUV. It's not something I'm mad about (life is too short) but I did HOPE for close to the EPA estimates. I think people who get closer to what the EPA says we should get are doing a lot more highway mileage than I do -- and it won't be until the summertime that I'll be able to put that theory to the test.

 

[mikey1981]

the avg for this car, if you drive it around town even w/some highway, is going to be 14-16.

if its the reverse like 80% highway, u may reach near 20.

if its all highway, u will be in the low 20's.

i think that, in a nutshell, is what to expect.

 

[Hasplode]

the avg for this car, if you drive it around town even w/some highway, is going to be 14-16.

if its the reverse like 80% highway, u may reach near 20.

if its all highway, u will be in the low 20's.

i think that, in a nutshell, is what to expect.

I can't argue with that. Over the first 11,000 miles (90-95% highway) I'm averaging 20.3 MPG.

 

[simonxda]

Compare to this and a bimmer then I think its a little more depend on where you drive. I did mine few week on 80% highway and its 480Km(298miles) for 60L(13.2G) and fully city for 350Km(217miles),(60L/13.2G). This car consume the same as other made on highway but does different on city. I guess its the gear ratio that makes the different. Cause I don't use up to 5th gear on city, only 4th. So if you live in and do mostly city, you will expect a higher consumption.

 

[azcat]

This vehicle has a "saddle" tank--it stretches across the drive shaft running to the rear differential (or the place where the drive shaft would be), with a lump in the middle and two lobes dropping down on either side (left and right). That makes it very, very difficult to fill. Even a different pump at the same station will shut off at different levels. I've added as much as a gallon after the pump shut off the first time (and I'm not saying I overfilled nor did the fuel come out the filler neck).

I think one cause of these "poor" or "bad" gas mileage results comes from a "short" fill (not getting the tank completely full) followed by a "long" fill (actually getting it full). Now that I've seen the tank (I crawled under it), and based on my experience with an AWD Santa Fe with the same tank design, I've 1) made an effort to really get the tank full; 2) made an effort to use the same pump at the same station for refueling; and 3) blown off (or taken with a grain of salt) any mpg calculations that are from different pumps, even at the same station. Doing this, I've gotten, on several tanks, over 23 mpg, on mostly Interstate driving.

Other than the "short fill/long fill" issue, factors that affect the mpg are:

1. Your foot. Easy driving gets better mileage. Duh. It seems especially true in this vehicle. Consistently running over 2.5k rpm will kill mpg.

2. As CX7Rabbit said, the type of fuel. Using the same pump at the same station, I still get crappy mileage (17-18) when the blend is 10% ethanol. Ethanol has a lower BTU per gallon than gasoline. It's physics. Like gravity, it will have its way. Get over it.

3. The type of driving you do. I get my best mpg setting the cruise on 74 mph and letting him run for about two hours on the Interstate, with a minimum of braking, hill climbing, or accelerating-to-pass. Difficult? Yes. PIA? Yes. Worth it? Probably not. Life's too short to piss and moan about mpg.

My $0.02. (butt)

 

[CXRabbit]

I think one cause of these "poor" or "bad" gas mileage results comes from a "short" fill (not getting the tank completely full) followed by a "long" fill (actually getting it full). Now that I've seen the tank (I crawled under it), and based on my experience with an AWD Santa Fe with the same tank design, I've 1) made an effort to really get the tank full; 2) made an effort to use the same pump at the same station for refueling; and 3) blown off (or taken with a grain of salt) any mpg calculations that are from different pumps, even at the same station. Doing this, I've gotten, on several tanks, over 23 mpg, on mostly Interstate driving.

I agree with you on most of your other points, but this one, not really. My last three tanks MPG has been 14.79, 13.12 and 13.03... even if what you say is true and I might have used a gallon less of gas than I thought, it would only change those numbers by about 1 MPG. My last fill up the car took 15.04 gallons of gas... but let's assume I ACTUALLY only used 14.04 gallons... My MPG would still only be 13.96 MPG for the 196 miles I drove.

I do agree that for the best accuracy you have to try to get the tank full the same way every time... I don't know about you, but I have a HARD TIME at some gas stations just getting the nozzle to nessle in there properly. A lot of the pumps at stations around here have those stupid rubber/plastic flexi-things around the nozzle and it's a tight fit on the Mazda (and a real pain in the a$s).

 

[simonxda]

Hi CXRabbit, Wonder why I can't fill up my gas tank till 15gallons(68Liter) I can only does 61L(13.5G) or 62L when my empty lights up? 15gallons must be really empty..

 

[CXRabbit]

Getting 15 gallons in the tank the gauge is reading below a 1/4 of a tank. My warning light came on only once and when I filled up that time it took about 15.8 gallons. Capacity of the tank is just a tad over 18 (18.2 if I remember correctly).

 

[1Sleepy93]

If you aren't filling up with the needle directly on E, you're just filling up too soon. LOL

I routinely stick about 16.x gallons in the tank.

 

[mikey1981]

yea im at a routine 15.8/16.1 gallon fillups.

At first I thought the aggressive driving would kill the tank, but in reality, u might as well drive like how youd want to drive vs trying for consumption. What is 1 MPG worth to you working this truck thru city streets? You can either drive like you actually care about MPG (which is flat out boring and not the point of this car) or u can really get into it and enjoy your driving, to me, the difference in MPG (city driving) aggresive vs conservative is minimal, if non existant. You will get low numbers driving in the city no matter what style you want to call your drive thats just how this truck works.

 

[Alpha Wolf]

Seems odd.

I have yet to get the warning light on as I usually fill up around 1/4 tank and have gone over 255 miles and still not light 50/50 highway/city.

Now I think it is mostly how people drive. Because as soon as my wife takes if for a drive, the same amount of gas is used for 211 miles as she constantly kicks in the turbo and makes fast starts and hard merges as she like the feel of it going.

 

[mikey1981]

maybe this is a misconception amongst people, but turbo is always flowing, its not like there is an on/off button.

 

[Alpha Wolf]

maybe this is a misconception amongst people, but turbo is always flowing, its not like there is an on/off button.

Obviously you fail understand the basic operating principles of a turbo charger.

A turbo charger is driven by exaust gases.. These gases work on vanes within the rotor and housing of a a turbo to cause the central portion to spin. One the other side of the turbo are more vanes that are within the air intake portion of the engine. Here it acts as a pump.

While the turbo charger is indeed always spinning at some speed. It does not create boost, ie an increase in intake manifold pressure over standard atmospheric pressure, until the turbo is spinning at a high enough speed that the vanes in the intake track can cause this increase in pressure over atmospheric pressure on the output side. This characteristic is what causes "TURBO LAG". An increase in volume of air going into an engine requires and equal increase in the amount of gas in order to maintain the proper air/fuel ratio for efficient combustion. This increase in necessary fuel means higher fuel consumption. So boosting your engine effectively makes is larger. Large engines require more fuel. Hence poorer mileage.

In our cars this speed is reached when the engine rpm reaches 2,500 rpm. At that rpm, there is enough hot exhaust gas being produced to spin the turbo fast enough to increase the pressure in the engines intake ports. Below that the engine is not being boosted and hence strained. When you boost an engine you create increased heat and pressure to create the increase in power. This increases stresses and loads on rings, bearings, connecting rods, , crankshaft, pistons, etc... Turbos allow you create power when needed but to then allow the engine to operate in an unboosted mode for higher economy and longer life.

Also to increase velocity enough to create boost at idle you must reduce the turbo exhaust intake sufficiently along with redesigned vanes to create enough velocity to spin the turbo fast enough to boost. The problem is now the max flow capacity of the exhaust intake to the turbo is now reduced. Meaning you create less power at higher rpms. Our cars intake track to the turbo is smaller than that on the Mazda 6 to create boost 500 rpm sooner to reduce turbo lag and boost torque at the lower end of the operating range. This change cost us about 30 hp in top end HP as a trade off.

So if you hit the gas hard enough to get the engine to 2500 and above each gear, you will greatly increase your fuel consumption. You are now feeding fuel to match the now increased air volume going into the engine. More air, more fuel.

So by driving lightly and shifting early and keeping the rpms below 2500 you will greatly increase you fuel economy. In this rpm range it will act like the tiny 2.3 liter motor without a turbo, just don't expect it to jump like a 5 liter V8 would if you hit the gas while in this rpm range.

To get power, manually downshift until rpms are 3,000 rpms or higher then hit it.

If you want high power at low engine speeds you need a bigger engine, nitrous or a supercharger driven by the crankshaft.

 

[azcat]

I agree with you on most of your other points, but this one, not really. My last three tanks MPG has been 14.79, 13.12 and 13.03... even if what you say is true and I might have used a gallon less of gas than I thought, it would only change those numbers by about 1 MPG. My last fill up the car took 15.04 gallons of gas... but let's assume I ACTUALLY only used 14.04 gallons... My MPG would still only be 13.96 MPG for the 196 miles I drove.

I do agree that for the best accuracy you have to try to get the tank full the same way every time... I don't know about you, but I have a HARD TIME at some gas stations just getting the nozzle to nessle in there properly. A lot of the pumps at stations around here have those stupid rubber/plastic flexi-things around the nozzle and it's a tight fit on the Mazda (and a real pain in the a$s).

I am truly sorry that you have to deal with the "save the whales and icebergs for Jesus" fuel filler thingies.

My fuel low light comes on mostly when I have over 300 miles on one tank. I really, honestly, respectfully think that you're not getting it full. Or, you're filling up with Al Gore approved, low global warming, high ethanol fuel. Or maybe Exxon is just screwing y'all in the the Northeast. Really. Why these crazy differences in mpg?

I've quit driving with my foot in the intake (not that you do, still respectful), and my mpg is the same or better than the previous 2.7 liter AWD Hyundai Santa Fe. I'm still happy.

"Variability is the enemy." What are you doing different to cause these differences in mpg? Different stations? Different pumps? Too damn cold to mess around with filling it? 13 mpg?? I mean, really, I got better than that with my 1999 4x4 Dodge Dakota with the Full Testosterone V-8 Package. What's changed????

 

[CXRabbit]

LOL Azcat (re: iceburgs for jesus)

Oh, we are living with 10% ethanol fuel here in NY and "winter mix" gas and it's certainly hurting the numbers. I've tried filling up at different stations and do the best I can to get it full. And I get the gallons in I expect to based on what the gauge is reading. When the light is on I get almost 16 gallons in, and really, that's just about right.

I know my numbers are so low at least partially because I do so much around-town, stop-n-go, short distance driving. It KILLS the mileage. Only time I got over 18 mpg was when there was some significant highway time (I guessed around 40%). Some of it's probably the winter gas. Some of it's probably that I like turbo boost. I wonder if some of it has to do with the latest PCM update (but I've gotta get on the highway more to prove that).

13 mpg hurts... but ultimately I didn't buy the car for it's efficiency (luckily I wasn't counting on 20 mpg).

 

[mikey1981]

Obviously you fail understand the basic operating principles of a turbo charger.

A turbo charger is driven by exaust gases.. These gases work on vanes within the rotor and housing of a a turbo to cause the central portion to spin. One the other side of the turbo are more vanes that are within the air intake portion of the engine. Here it acts as a pump.

While the turbo charger is indeed always spinning at some speed. It does not create boost, ie an increase in intake manifold pressure over standard atmospheric pressure, until the turbo is spinning at a high enough speed that the vanes in the intake track can cause this increase in pressure over atmospheric pressure on the output side. This characteristic is what causes "TURBO LAG". An increase in volume of air going into an engine requires and equal increase in the amount of gas in order to maintain the proper air/fuel ratio for efficient combustion. This increase in necessary fuel means higher fuel consumption. So boosting your engine effectively makes is larger. Large engines require more fuel. Hence poorer mileage.

In our cars this speed is reached when the engine rpm reaches 2,500 rpm. At that rpm, there is enough hot exhaust gas being produced to spin the turbo fast enough to increase the pressure in the engines intake ports. Below that the engine is not being boosted and hence strained. When you boost an engine you create increased heat and pressure to create the increase in power. This increases stresses and loads on rings, bearings, connecting rods, , crankshaft, pistons, etc... Turbos allow you create power when needed but to then allow the engine to operate in an unboosted mode for higher economy and longer life.

Also to increase velocity enough to create boost at idle you must reduce the turbo exhaust intake sufficiently along with redesigned vanes to create enough velocity to spin the turbo fast enough to boost. The problem is now the max flow capacity of the exhaust intake to the turbo is now reduced. Meaning you create less power at higher rpms. Our cars intake track to the turbo is smaller than that on the Mazda 6 to create boost 500 rpm sooner to reduce turbo lag and boost torque at the lower end of the operating range. This change cost us about 30 hp in top end HP as a trade off.

So if you hit the gas hard enough to get the engine to 2500 and above each gear, you will greatly increase your fuel consumption. You are now feeding fuel to match the now increased air volume going into the engine. More air, more fuel.

So by driving lightly and shifting early and keeping the rpms below 2500 you will greatly increase you fuel economy. In this rpm range it will act like the tiny 2.3 liter motor without a turbo, just don't expect it to jump like a 5 liter V8 would if you hit the gas while in this rpm range.

To get power, manually downshift until rpms are 3,000 rpms or higher then hit it.

If you want high power at low engine speeds you need a bigger engine, nitrous or a supercharger driven by the crankshaft.

so far its been my experience with this car, that it really doesnt go anywhere UNTIL you reach 2, 2.5k , so IN ESSENCE, the turbo is flowing. Mazda , since most of us already know, released that update to send power under 2k. This would mean to me that unless you were riding down a hill, the turbo was kicking while you were moving at all times.

Moving the CX-7 and under 2.5/2k really dont go in the same sentence for city driving. Highway, then obviously you wont be reving the engine unless ur lane changing.

90% of my driving is in the city, and this truck just doesnt coast down streets under 2k

 

[mikey1981]

thanks for the long winded and 32423423 post about how turbos work, tho

 

[Alpha Wolf]

I have had mine flashed.

The ECM does not control turbo speed unless it uses movable vanes which as far as I know it doesn't. It does appear to control transmission auto shift points, fuel, and ignition timing.

It appears that when stock the engine would quickly shift into 5th in town doing 35mph. Now it will not go into 5th in town. 4th is max. It also stays in lower gears longer even when light footing the gas. So now it takes extremely light foot to keep it from hitting the 2,500 rpm magic turbo speed rpm.

They did not "speed up boost" as this is still a function of engine rpm which controls the volume of exhaust gases hitting the turbo vanes. But by changing the fuel and ignition they have boosted some power down low and the tranny now appears to stay in lower gears longer, again helping to get you to the magic 2,500 rpm number sooner. The result is to allow you to get to 2,500 quicker even at small throttle positions.

While this smooths the turbo hit, I would guess it will also mean you will need even more restraint on the gas pedel as now it will go into boost by hitting 2,500 sooner. In auto mode it seems to hit 2,000 rpm regardless of how easy you touch the gas.

So this will make it a smoother driving car. But I fear it will make it even harder to get 24mpg than before.

Just my thoughts. (hi)