Gas Guage

[iced_theater]

The filler neck is not designed to be filled with fuel, that's why manufacturers tell you not to top-off. People here had a hissy fit about the latest fuel filler tube recall, imagine how much worse it would be if you exited the gas station and got rear ended by a drunk going 60 mph. It takes a number of miles to burn off the fuel that is outside the fuel tank and the fuel shut-off flapper valve inside the tank can't operate as designed when it's submerged. I fail to see a similarly compelling argument why topping off is necessary.

Unless of course you want to increase your chances of gaining admittance to this exclusive club:

https://mpora.com/multi-sport/there...but-these-have-got-to-be-some-of-the-silliest

I think you're more likely to be killed from the initial 60 mph hit compared to the hazard of a couple gallons of fuel in the filler neck. I top off my tank and have for 50-60k miles in the CX-5 and have had no problem at all with it damaging anything. I top off since all gas stations and sometimes different pumps at the same gas station shut off at different times. Topping off means I know my fuel economy results are accurate and I get the added benefit of filing up every 500+ miles

 

[yugrus]

If you top it off the way that the fuel sits above the charcoal canister level, if ECU decides to vent the tank, the fuel might end up in the canister. This isn't good for emissions, so the said ECU might pop a nice yellow light on the dash if it detects a problem with subsequent purging of the above canister. This doesn't happen all the time, but it does. I've had that at my shop more then once during my ownership. Very tough to diagnose, often takes multiple visits and useless part replacements, depending on the mechanic's abilities.

 

[MikeM.]

I think you're more likely to be killed from the initial 60 mph hit compared to the hazard of a couple gallons of fuel in the filler neck.

That's true but it's a red herring argument. The fact that one or more occupants might die in the initial impact does not mean that any potential injured survivors want to burn to death in the resulting fire. Injured people cannot always self-extricate without assistance and this is why uncontained fuel is dangerous in an accident.

That's one good reason not to top off.
Another good reason is to avoid the possibility that the car decides it needs to purge the vapor recovery system while fuel is above the level of the charcoal canister. Why risk it?
A third good reason is because the manufacturer cautions that this is a dangerous practice and instructs not to do it. They have no reason to make this s*** up.

But the world is full of ignorant and stubborn people and, if you're the idiot filling up, you are generally free to do it however you want. Even if the reason you top off is because that's how you've always done it on old school cars and you never had an issue. If this describes you, there's a better than 50/50 chance you've used an old cotton rag in place of a lost/stolen fuel filler cap. Kinda like a big Molotov cocktail on wheels.... (beer)

 

[iced_theater]

Another good reason is to avoid the possibility that the car decides it needs to purge the vapor recovery system while fuel is above the level of the charcoal canister. Why risk it?
A third good reason is because the manufacturer cautions that this is a dangerous practice and instructs not to do it. They have no reason to make this s*** up.

But the world is full of ignorant and stubborn people and, if you're the idiot filling up, you are generally free to do it however you want. Even if the reason you top off is because that's how you've always done it on old school cars and you never had an issue. If this describes you, there's a better than 50/50 chance you've used an old cotton rag in place of a lost/stolen fuel filler cap. Kinda like a big Molotov cocktail on wheels.... (beer)

I can come up with a ton of hypothetical scenarios as well, but in the 100's of thousands of miles I've driven in cars ranging from the '60's to today, I've never had a car mess up because of too much fuel in the tank.

As for your 50% chance; did you also know there is a 81% chance that all statistics are made up?

 

[bmninada]

In NJ we have attendants to fill up the gas and its illegal to do it ourselves. They wont budge in terms of top off.
However, I agree with Mike. The gas meter is extremely accurate. I got it down to zero when cruising into Costco gas and the fill amount was 13.5
Next time, I had it down back to zero and went on till there was no gas and the car stopped. I put in 1 gallon (the gallon I carried) and then at the gas station they clocked me at 14.8. I would say, out of that 1 gallon I did put maybe I used .2 gallon to reach the gas station. The gas meter still read 0.

 

[banjos-n-beer]

Why would someone purposely run their car dry just to test/confirm/deny mpg ratings?!!?

Are folks really that concerned about the reading of how many miles are left to travel on the dashboard? Proper refueling schedules should alleviate that concern. Why can't you inconvenience yourself with a stop at a gas station to prevent such a preventable scenario?

Seems like a stupid unnecessary risk.

 

[CX5_Pete]

Why would someone purposely run their car dry just to test/confirm/deny mpg ratings?!!?

Are folks really that concerned about the reading of how many miles are left to travel on the dashboard? Proper refueling schedules should alleviate that concern. Why can't you inconvenience yourself with a stop at a gas station to prevent such a preventable scenario?

Seems like a stupid unnecessary risk.

I travel a lot for my job and it's nice to know how much I can squeeze out of my tank before i really need it fill it. Just knowing puts my mind at ease.

 

[banjos-n-beer]

Why do you need to push it so far? Why would gassing up at 1/8-1/4 tank be such an inconvenience or detriment?

 

[MikeM.]

I can come up with a ton of hypothetical scenarios as well, but in the 100's of thousands of miles I've driven in cars ranging from the '60's to today, I've never had a car mess up because of too much fuel in the tank.

I've never had a problem either. But I stopped "topping off" back in the 1980's. Guess who's more likely to experience an issue due to topping off:

a) Someone who usually tops off or
b) Someone who never tops off?

I'll give you a hint:

The answer is not "b".

I bet you've never had your post 2005 car totaled from being rear ended at high speed when your tank was filled up into the fuel filler tube. Yeah, very low probability. And even lower it would happen in the first few miles after topping off. But it will never happen if you never top off. That's 100% certain.

As for your 50% chance; did you also know there is a 81% chance that all statistics are made up?

That statistic is from 2012. In 2015 it was found to be 86%.

 

[MikeM.]

Why do you need to push it so far? Why would gassing up at 1/8-1/4 tank be such an inconvenience or detriment?

Sometimes I drive hundreds of miles without passing a gas station. I've filled up at 1/2 tank before to avoid having to drive 15 miles out of my way to find gas. But if I know there will be fuel available within around 1 gallon of empty, I won't even fill up at 1/8 of a tank. Why bother? Knowledge is power. If you know how far your vehicle can actually go with a high degree of certainty, you can make better decisions than someone who hasn't a clue what the facts are.

 

[banjos-n-beer]

+\- 10-15 miles seems insignificant to me. I'd think it's rare to travel with such inadequate planning in this day and age of smartphones, mapquest etc.

Further, anyone that routinely measures their fuel consumption should be able to tell how much travel is left on a tank of gas. Regardless of what the dash readout states.

 

[MikeM.]

+\- 10-15 miles seems insignificant to me. I'd think it's rare to travel with such inadequate planning in this day and age of smartphones, mapquest etc.

Your original question was "Why do you need to push it so far? Why would gassing up at 1/8-1/4 tank be such an inconvenience or detriment?". I know I still have 180 miles left on a 60 mph highway when I'm down to the 1/4 tank mark. Why would I fill up three hours early if I knew there fuel available on my route 2 1/2 hours down the road?

Further, anyone that routinely measures their fuel consumption should be able to tell how much travel is left on a tank of gas. Regardless of what the dash readout states.

No. This was discussed when the 2013 CX-5 was first released in early 2012 and, while plenty of us speculated about how much fuel was left, nothing was as definitive as the "running until sputter" test was performed. Keep in mind, the AWD and FWD models use different fuel tanks and different fuel metering strategies to try to achieve similar fuel level reporting goals (the AWD has two separate fuel measuring devices). Therefore this test is only directly applicable to AWD models.

Interestingly, although Mazda claims there is 2.6 US gallons of remaining fuel level in the 2013 AWD and FWD CX-5 when the low fuel level indicator illuminates, they indicate differing amounts of "invalid fuel" between the FWD and AWD. I interpret "invalid fuel" to mean the fuel remaining in the tank once the fuel pump starts to suck air. For the 2013 AWD this is 0.12 US gal. and the FWD has 0.359 US gal. (or about three times as much unusable fuel).

If my interpretation is correct, the AWD has 2.48 US gal. of useable fuel when the light illuminates
and the FWD has 2.241 US gal. useable fuel left. Rounding error from tenths of a liter to gallons accounts for the specification to thousandths of a gallon, obviously there are variables greater than that.

Apparently the low fuel warning light is operated by a different means than the primary fuel sender because it's illumination does not occur simultaneously with the extinguishing of the last fuel level bars (from experience). Mazda specifies a range of remaining fuel that will result in only the last fuel level bar being active and it is the same range regardless of FWD or AWD:

1.6 US gal.-2.1 US gal.

I do not believe the "invalid fuel" is counted in this number. In other words, there should be approximately 1.6 US gal. of useable fuel when the last fuel bar goes off. Of course the amount of useable fuel could vary slightly depending upon the attitude of the vehicle both when the fuel bar extinguishes and also when the pump starts sucking air.

 

[CX5_Pete]

Why do you need to push it so far? Why would gassing up at 1/8-1/4 tank be such an inconvenience or detriment?

Ease of mind. It's just good to know. For example: when the gas light goes on and the nearest gas station is too expensive, I have an idea of how far I can go to find a more affordable one (most likely a Costco and get a nice lunch for $1.50).

Keep in mind, it's not like I run it dry all the time. Like Mike says, knowledge is power.

 

[banjos-n-beer]

Fair enough. But personally, I don't run my vehicles dry, nor do I rely on the silly low fuel warning light.

 

[bmninada]

Sometimes I drive hundreds of miles without passing a gas station. I've filled up at 1/2 tank before to avoid having to drive 15 miles out of my way to find gas. But if I know there will be fuel available within around 1 gallon of empty, I won't even fill up at 1/8 of a tank. Why bother? Knowledge is power. If you know how far your vehicle can actually go with a high degree of certainty, you can make better decisions than someone who hasn't a clue what the facts are.

Yep - that's why. Actually, I did not find a single source which gave me for certain after dial = 0, how much still left.

 

[banjos-n-beer]

Ps Mike- cute comment at the end (re: clues). But I'm not going to waste my time trading personal barbs.

Having said that, don't vehicles use the fuel to help cool the fuel pump in the tank? I was under the impression going below a certain level could cause unnecessary stress to the fuel delivery system.

Lastly, I'm not one to fret over $.05-10/gal. If I need gas, or suspect I will need it I just buy it. The only places I try to avoid are highway reststops. But if needed I'll pay the convenience premium to get enough to get to my destination comfortably.

 

[MikeM.]

Ps Mike- cute comment at the end (re: clues). But I'm not going to waste my time trading personal barbs.

No personal barb intended and I'm not sure why you took it that way. My point was simply that knowledge is power versus not having a good idea (or clue) exactly when it will run out.

Having said that, don't vehicles use the fuel to help cool the fuel pump in the tank? I was under the impression going below a certain level could cause unnecessary stress to the fuel delivery system.

No, the fuel pump is built to withstand heat, as long as it has fuel flowing through it, it will be fine.

But if needed I'll pay the convenience premium to get enough to get to my destination comfortably.

Being able to competently use the last quarter tank without running dry can be very convenient (with no price premium to pay). That's why I say knowledge is power. I learned this because my two Sport-touring motorcycles only have 5.5 gallon tanks. On the open road this provides a range of only 205-300 miles depending primarily upon speed and ambient temperature. I'm not about to give up 50-75 miles to avoid using the last 1/4 tank. I typically ride 400-600 miles/day and It's a rare day I need to stop three times for fuel.

 

[banjos-n-beer]

Mike- I suspect you spend more time in remote areas than average owners. If so that makes more sense as for the need for more exact calculations. I'm rarely outside range of a gas station, even when on camping trips because I plan accordingly.

Thx for the info on the fuel system. Do you have, or can you provide documentation to back those statements up? I'd be happy to read it if so (providing it's not something already printed in the owners manual that I've overlooked).

Regarding highway stations, I don't sweat it if I need an extra 5 gallons for peace of mind. That's a whole whopping $1 extra on a $0.20/premium. Plus the girlfriend usually has to pee. So I'm already making the stop in the first place.

 

[MikeM.]

Mike- I suspect you spend more time in remote areas than average owners. If so that makes more sense as for the need for more exact calculations. I'm rarely outside range of a gas station, even when on camping trips because I plan accordingly.

True. My ski cabin is on a dead end highway (ending at a ski area). My cabin is an 18 mile round trip to the nearest gas station (which has very high prices anyway) and the ski area is in the opposite direction (round trip 35 miles). My tank has almost 100 miles on it by the time I get to my cabin and I want to be able to string together consecutive round trips to the ski area without having to take an unnecessary 18 mile round trip in the opposite direction simply to re-fuel so I can ski one or two more days. If the road is covered in ice it can take an hour. So it's not uncommon for me to run with the low fuel light on. Sometimes I'm running with the light on just to make it to the rural gas station but, more often it's to make it to my preferred station (better fuel and lower prices).

Thx for the info on the fuel system. Do you have, or can you provide documentation to back those statements up? I'd be happy to read it if so (providing it's not something already printed in the owners manual that I've overlooked).

I'm not sure why it is grayed. When you analyze this you will get the most out of it if you use the native units (liters). Some of the gallon figures on the right side are truncated at the decimal point and are not accurate.

Regarding highway stations, I don't sweat it if I need an extra 5 gallons for peace of mind.

Peace of mind is a state of mind. Knowing your remaining range with a high degree of certainty provides peace of mind. Not knowing means you have to top up to achieve it. I haven't run out of fuel yet (and I don't plan to).

 

[banjos-n-beer]

Peace of mind also helps alleviate elements out of ones control. Such as idling for an hour or two due to a highway wreck. Often one creeps along thus preventing an opportunity for shutting down the vehicle. Just another reason I see no need to push the limits of frugality.

Ps- thx for the chart. I'll take a gander when I'm not using my phone.