How far on a tank of gas?

[ronmort]

The amount of gasoline weight you are carrying around will affect your gas mileage in such miniscule increments, that it will be immeasurable. Your driving behavior is the biggest determining factor on gas mileage. If you drive more aggressively cause you think you're carrying less weight, it's going to erase any and all fuel economy by driving with an empty tank and saving 90lbs of weight.
Ultimately it's your car and this is America, so you can do what you want. By all means, if you really think this is fun or a good idea, have at it. Hopefully the stress you are putting on the fuel pump will manifest during the warranty period. If not, the money you save on gas can be used to replace the fuel pump.

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I was not suggesting that running down to empty is a good idea. I was simply stating that I didn't see any mention of fuel weight in any discussions. The difference between a full tank and empty is about 120lbs... about 3% of he total weight of the vehicle. Easily calculable in fact... a difference of about .75 mpg.

 

[TJPark01]

I was not suggesting that running down to empty is a good idea. I was simply stating that I didn't see any mention of fuel weight in any discussions. The difference between a full tank and empty is about 120lbs... about 3% of he total weight of the vehicle. Easily calculable in fact... a difference of about .75 mpg.

You're making an assumption that you can drive around any meaningful distance on <1 gallon of gas all the time to get to that .75mpg. In principle, you may be correct. In practice, your logic doesn't quite work out that way. If you want to save weight, trying to do it with the least amount gasoline in your car, seems very impractical. (not to mention the fuel pump issue).
Dad: Kids you have to walk home from school from now on
Kids: What, Why?
Dad: Your puberty is negatively affecting my average MPG. Sorry.

 

[vega]

I've got 540 miles on a round trip to Michigan (65-75 MPH) as a high. The car had 2400 miles on it then. 33.6 MPG

I've had a tank empty at 486 miles, combined city 40%, highway/rural 60%. 28.1 MPG

I always fill up between 1/4 and 1/8 tank. The car does seem to be improving with more miles on the clock, now at 5750 miles.

It will be interesting to see what it does when I head to Florida this winter.

 

[wallymn]

while I agree , as the manual states, that running the car dry (empty) isn't good for the fuel system or exhaust system, I should be able to run a "low" tank from time to time.

as for sediment,,, I have found the fuel pumps in most tank going back to the seventies are slight off the floor of the tank , I don't think it is likely it would pick up , also at most that should/would foul the fuel filter mounted at the gas tank..

I could see arguing the fuel filter will need premature replacement...

 

[ttsig]

I'm not sure what you guys are gaining by driving around with very low fuel levels.
From the owners manual Page 382:
Avoid driving with a very low fuel level.
If you run out of gasoline, it could
cause the engine to misfire and result
in excessive loading of the catalytic
converter.
Failure to observe these precautions
could result in damage to the catalytic
converter and to your vehicle.
Additionally, such actions could void your
warranties.

I didn't meant to imply that I'm gaining anything, other than about one extra day of driving between gas stops. It's not that big of a deal. I've found that I can drive my Genny well over 75 miles after the "low fuel" light comes on so there's still 2-3 gallons of gas in the tank at that point. I generally fill up in the next 40-50 miles so at no point is there less than a gallon in my tank. I'm not sure what Hyundai would consider "very low fuel" as that's a pretty "fluffy" definition from a legal perspective.

The time I referred to when I ran out of gas and had to coast to a station was simply a mistake on my part. I knew I needed gas before I headed out on my morning commute but forgot to stop before I left town. Once I leave town there's about a 25 mile stretch to start my commute with no service station and I was well into the first 12 miles before I remembered how low on gas I was (I guess I woke up about that point ) and at that point the next station was still over 10 miles away so I drove ~25 miles further than I intended. That's basically a gallon of gas that's normally still in the tank when I fell up. Would 5% be "very low fuel"? I don't know but I've never felt my car misfire or otherwise misbehave at this fuel level.

I guess what I'm saying is, it's hard for me to believe that filling up at 25% of a tank, or filling up at 5% of a tank is really all that different from a reliability perspective and it means I only have to stop for gas every 4th day instead of every 3rd. That's about 15-20 less stop for gas ever year.

I'm not arguing that my approach is somehow superior though, it's just what I do, I can't really explain it, but I hate stopping for gas, so I like to use a high percentage of the tank. I've always done it and I expect I'll continue to do it.

 

[TJPark01]

I guess what I'm saying is, it's hard for me to believe that filling up at 25% of a tank, or filling up at 5% of a tank is really all that different from a reliability perspective

Are you coming to this conclusion by "feel" or "intuition". I'm more inclined to follow the manufacturers recommendation, but that's just me.

I'm not arguing that my approach is somehow superior though, it's just what I do, I can't really explain it, but I hate stopping for gas, so I like to use a high percentage of the tank. I've always done it and I expect I'll continue to do it.

If it works for you keep at it.

 

[ttsig]

Are you coming to this conclusion by "feel" or "intuition". I'm more inclined to follow the manufacturers recommendation, but that's just me.

But the manufacturers "recommendation" is basically just to not run a "very low fuel level". That's a very vague statement that means different things to different people. It goes on to say that running out of gas may cause the engine to misfire and other problems. Since that's all in the same paragraph it appears that their suggestion of not running at a "very low fuel level" is so that you don't inadvertently run out of gas, which I would agree is bad for your engine, as well as your safety. But, if I run my tank low, but never run out of gas, am I really not following the manufacturers guideline?

 

[TJPark01]

But the manufacturers "recommendation" is basically just to not run a "very low fuel level". That's a very vague statement that means different things to different people.

True.

Having to coast my Genesis for a over a mile and just barely coasting into a rural gas station definitely let me know how far I can push the gauge on the Genesis before I really, really need gas. I put in something like 19.5 gallons on that fillup, while my normal fillup is in the 18.5 gallon range (the official capacity of the 3.8 is 19.3 gallons).

Driving with <1 gallon of gas in the car would probably fall into the category of "really not following the manufacturers guideline". Since it works for you keep at it.
[nomedia="http://www.youtube.com/watch?v=TuEdU_lrtZk"]YouTube- Kramer test drives car on Seinfeld[/nomedia]

 

[mikec]

When the tank is down to just a gallon or two fuel slosh when cornering, accelerating/decelerating, or even going up/downhill can expose the fuel pickup to air. That'll lead to fluctuations in the fuel pressure which screw up the engine's air:fuel ratio... leading to misfire or momentary emissions hiccups.

Also, if you leave the car parked for a few days with a low fuel load, natural humidity can condense inside the tank. That moisture screws things up two ways:
1) mixes with the low fuel quantity. A little moisture mixing with several gallons of gas is no big deal... but when there is only 1 or 2 gallons in the tank (and thus a lot more air space ==> more moisture volume) the ratio of water to gas increases. That can lead to engine running problems and the water isn't friendly to the fuel pump and especially not to the fuel injectors.

2) moisture in the tank can eventually lead to rust forming on the inside walls of the tank. Rust in the tank clobbers fuel pumps. It's a really nasty problem for folks trying to resurrect older cars.

If you know the car will be parked for weeks or more, fill the tank! If it'll be parked for months (folks that garage a car for the winter perhaps) then use quality gas and a fuel system stabilizer. Old gas (sometimes "only" 6 months old, usually more like a year or two) decomposes into a varnish-like sludge that gums up fuel pumps and injectors.

If the car isn't parked, then running the tank low isn't a big deal as long as it isn't so low that fuel slosh lets air into the pickup.

Back to the original topic: the first long trip I took with my 4.6 was from Cypress (SoCal) to central Utah. I made it to St. George (southern tip of Utah) on the first tank with about 2 to 3 gallons to spare: 380.5 miles, 24.7 actual MPG. (26.4 claimed MPG on the dash display... reality=94% of the car's estimate.) That also included lots of up-n-down hill climbs, with a net gain of several thousand feet. Return trip: 451 miles between fill-ups, 16.1 gallons, 27.8 actual MPG. The dash gauge claimed I had 1/8th of a tank left... so maybe another 50 miles?

mike c.

 

[ASHDUMP]

Jeez - you would think by now the engineers would have figured this out. Maybe its a back door way to get service done on a certain percentage of cars. I've never had a fuel pump go on me over the years... but then again, I've only owned 6 vehicles.

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[ttsig]

My gas barely has time to see the tank before it's burnt so I don't have a lot of concern with the gas aging or absorbing moisture but those are certainly valid concerns. Heck, since most modern fuels contain ethanol they absorb more water than fuels just a few years back. E-10 fuels, which are the vast majority of fuel on the market nowadays, have a recommended shelf life of only about 90 days because, in a humid environment (60-80%, pretty common in my area) they'll absorb water to their saturation point in that time. After they reach saturation the water will separate to the bottom of the tank which is obviously not good.

I'm not suggesting people run their cars to an empty tank, but I do believe that running to 1-2 gallons left is not that big a deal.

 

[ttsig]

Jeez - you would think by now the engineers would have figured this out. Maybe its a back door way to get service done on a certain percentage of cars. I've never had a fuel pump go on me over the years... but then again, I've only owned 6 vehicles.

I've replaced one fuel pump in ~25 years of driving, it was on a 1972 pickup truck with ~300,000 miles. It was electric (which was unusual back then) but not in the tank (inline). It was approximately 17 years old at the time it was replaced so it had a reasonable life but perhaps it would have made it longer if I hadn't run the tank empty a couple of times.

 

[Florida Boy]

For those of you driving down to virtually no gas in the tank, I'm curious about the miles you seem to be able to get once the system stops telling you how many estimated miles you have remaining. IIRC, the system stops counting at the estimated 30 miles left mark, correct?

Has anyone checked this? I've had a couple of occasions where I've had to travel 15-20 miles after the count ended and this raised my curiosity: just how far would it go beyond the estimated 30 miles, if in fact it does?

 

[STREETS]

I have not dared to go beyond the 30 miles. I have put 18.7 gallons in the 18.5 tanks- so I guess when it says 30 miles- it means it.

 

[ASHDUMP]

I keep track of all my fuel ups with www.fuelly.com

The most I've ever put in was 18.6 gal

 

[ttsig]

Has anyone checked this? I've had a couple of occasions where I've had to travel 15-20 miles after the count ended and this raised my curiosity: just how far would it go beyond the estimated 30 miles, if in fact it does?

Well, I almost always fill up within a mile or two once it's the below 30 mile mark and starts flashing "---", and usually just before this point, however, I've had two occasions where I drove a significant distance past this point, once was when I ran out of gas. Once was shortly after I purchased the car as I was on a long road trip in a fairly rural area. I watch as the display started flashing "---" and drove about 15 miles before reaching the next place for gas. I think I filled almost 19 gallons on that stop.

The next was when I ran out of gas as described in a post above. The display had just hit "---" as I rolled into my hometown from a long workday. My normal convenient station was closed, so I thought I'd just get gas the next morning before I left, however, as stated above, I left town that morning completely forgetting about it. I was quickly reminded when the car sputtered the first time, and then the engine died around 1/2 mile later. I was able to coast another mile to the station so I wasn't stranded, but it was close. According to Google maps the station where I filled up is 24.1 miles from my home, and I had probably driven about 2 miles after it rolled to "---" to get home the previous night, so that's about 26 miles, but since I had to coast a little over a mile that's really only about 25 miles.

I think they switch to "---" just because it's so difficult to estimate exactly how far you can go. If there's ~1 gallon left in the tank at that point you could likely drive gently and get very close to 30 miles, or you could drive very aggressively and only get 18, but the estimate seems close enough. While I like to run my tank pretty low, I generally suggest stopping ASAP once you see the "---" because you really don't have much left at that point.

 

[Florida Boy]

Agreed.

 

[STREETS]

ttsig- and you admit you ran out of gas...twice! Nothing worse than the feeling of the car sputtering, running on fumes and not exit or gas station for miles.

 

[ttsig]

ttsig- and you admit you ran out of gas...twice! Nothing worse than the feeling of the car sputtering, running on fumes and not exit or gas station for miles.

Nope, only once. I realized upon rereading that it sounded like I was referring to two separate instances of running out of fuel, but in the second paragraph I was just detailing the experience of running out to indicate just how far I had driven after the display flipped to "---" since that what he was asking about.

So yes, I admit to running out once in my Genny, but not twice, although technically I made it to the station so did I really run out of gas? Maybe I just planned my gas stop perfectly, or, as one of my coworkers suggested, I was practicing hypermiling.

 

[ronmort]

You are totally missing the point. Please don't reply to any of my posts in the future.