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What do you mean "these days"? In my 2000 Suburban the low fuel light came on with 7 gallons still in the tank, even in that it was 110+ miles of range. Is 16 years old still "these days"? Actually since you could get them in late 99 more like 17 years old.
The warning lights typically come on with about 3 gallons left, give or take based on manufacturer. I have even seen this spelled out in owners manuals. I cannot remember a time, since low fuel lights existed, that they came on as you were about to run dry...
I have no idea (or didn't till I read the 2nd post) why 'technically' one should keep one's tank fuller rather than emptier despite anything the manufacturer says but I grew up in the north and a) it was sometimes a very long distance to a gas station and b) often if the gas tank was low, the car would not start at 40 below (though I know there is more to it than that but 'superstition' is not always a bad thing).
I was brought up never to let a tank go below half and I don't, to this day.
On Sundays where I spend a lot of time these days, I could be as many as 70 miles from a gas station anyway. I don't like to play Russian roulette. Sometimes too gas supplies can be cut off or short and what will you do if the line is a mile long and already many of the pumps are empty .. happens about once a year around these (more southern) parts I have found and it can go on for weeks. If you live at the start of a supply line (or better yet where there are several coming in at the same spot) perhaps you don't have to worry about that but one never knows when a pipe will break somewhere and affect supply a 1000 miles away either.
The warning lights typically come on with about 3 gallons left, give or take based on manufacturer. I have even seen this spelled out in owners manuals. I cannot remember a time, since low fuel lights existed, that they came on as you were about to run dry...
Many cars now have much smaller gas tanks now in order to make the car weigh less (among other parts), so with cars that get a higher MPG the reserve once the light comes on is now in the 1-2 gallon range.
Ouch your poor fuel pump will be struggling to keep cool as it uses the gas to prevent overheating expect a in tank fuel pump replacement in the near future OP
also running it tHAT LOW YOU SUCK IN ALLL THE DEBRIS AND MUCK AT THE BOTTOM OF THE GAS TANK ALSO NOT GOOD
Eh..... on the debris thing..... that's pretty much a non-issue for getting it into the engine nowadays. The pickup screen in the tank and inline filter will take care of most of that. The pickup is at the very bottom of the tank. While you might speed up the clogging somewhat you're not very likely to get the debris into the engine. But it still isn't a good idea to run it that low.
Quote:
Originally Posted by Don in Austin
My Ford F250 diesel has dual tanks. For 100k miles when I used to tow my race car with the truck, i would switch tanks when the first tank ran out. Never a problem, other than ran slightly rough for a few miles.
Don in Austin
You've been extremely fortunate. It sounds like you had just enough fuel in the lines for the engine to run long enough to eventually purge the air out on its own. If you run it until the engine dies before switching I'd be shocked if it started back on its own without some help. This is very hard on a diesel engine.....
Location: We_tside PNW (Columbia Gorge) / CO / SA TX / Thailand
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Quote:
Originally Posted by Nlambert
... If you run it until the engine dies before switching I'd be shocked if it started back on its own without some help. This is very hard on a diesel engine.....
so true... while I would never consider this these days... it was std procedure in our fleet of Detroit 2 stroke diesel trucks that we would run a tank dry and switch over when she started to die (at least 3x / day).
Not recommended, and amazing that our fleet went millions of miles doing this.
Early VW air cooled (gas) had no Fuel gauge, but did have the 'trap door' lever that you hit with your foot as engine sputtered (more than usual) and ran out of gas. Unfortunately, that USUALLY happened at a steep incline Stop sign .
"Gravity Flow" in those days No $300 In Tank Fuel pumps. Fortunately VW's that I work on (up to 1999.5) have a very simple access port to swap out in-tank fuel pumps. 10 min, vs 10 hrs on a USA car / van / pickup truck + the danger / hassle of draining the fuel tank.
I have no idea (or didn't till I read the 2nd post) why 'technically' one should keep one's tank fuller rather than emptier despite anything the manufacturer says but I grew up in the north and a) it was sometimes a very long distance to a gas station and b) often if the gas tank was low, the car would not start at 40 below (though I know there is more to it than that but 'superstition' is not always a bad thing).
I was brought up never to let a tank go below half and I don't, to this day.
On Sundays where I spend a lot of time these days, I could be as many as 70 miles from a gas station anyway. I don't like to play Russian roulette. Sometimes too gas supplies can be cut off or short and what will you do if the line is a mile long and already many of the pumps are empty .. happens about once a year around these (more southern) parts I have found and it can go on for weeks. If you live at the start of a supply line (or better yet where there are several coming in at the same spot) perhaps you don't have to worry about that but one never knows when a pipe will break somewhere and affect supply a 1000 miles away either.
So if your truck has a 30 gallon tank, and it does not count three of those gallons, and you never go below half a tank, then:
1. You always have 16.5 or more gallons of gas that you do not use.
2. You are operating on a 13.5 gallon tank. If you get 15 MPG, then you are filling up every 200 miles as opposed to every 400 or so miles. I think you can at least safely run it down to a quarter tank (12.25 gallons).
Setting aside the idea of keeping your tank half full, it seems odd the car makers are basically tricking people into carrying around 3 gallons of gasoline they they will never use, or at least which the car mfgs want to make sure they never use. This is apparently to ensure there is always 3 or more gallons of gasoline in the car to keep the internal fuel pump cool.
It is interesting to me that manufacturers spend huge amounts of money and take risks to make parts that weigh a few ounces less, yet they encourage you to carry around several pounds (18) of excess fuel. Why not go back to the older, slightly heavier, fuel pumps and provide smaller gas tanks with a smaller or no hidden reserve. That would shave off more weight then many of the things they spend so much money on and end up with chintzy parts or parts that are crazy expensive to replace in order to cut an ounce or five. (With some vehicles, their extreme efforts to shave off a little weight makes no sense to me at all. I can put hundreds and hundreds of pounds of people or stuff in my truck, and the MPG remains exactly the same. What are they trying to accomplish by using cheaper lighter parts and making my truck 50 or 100 pounds lighter? I can see shaving off a few pounds in say, a Fiesta, might make some difference, but why put in less robust lighter parts in a 5500 pound truck? All that does is make things break more easily, the weight reduction is meaningless)
When your fuel pump was in your trunk or underneath your car and easily accessible, you did not need to carry around 18 or more pounds of extra gasoline to cool it, and you could replace most of them in less than half an hour. Sure the pumps weighed a tiny bit more (a matter of a few ounces), they did not cost more and they did not cost much of anything to replace if they wore out.
Maybe I should tell the car mfgs I found a way for them to shave nearly 18 pounds off every single car and massively reduce repair costs at the same time. Just go back to exterior fuel pumps and make all the gas tanks three gallons smaller.
On older cars, I think I have had maybe two or three fuel pump failures and always at 100K miles or more.
So if your truck has a 30 gallon tank, and it does not count three of those gallons, and you never go below half a tank, then:
1. You always have 16.5 or more gallons of gas that you do not use.
2. You are operating on a 13.5 gallon tank. If you get 15 MPG, then you are filling up every 200 miles as opposed to every 400 or so miles. I think you can at least safely run it down to a quarter tank (12.25 gallons).
Agreed. You should be safe to run down to 1/4 - 1/8 tank without worry of damaging the pump.
Quote:
Originally Posted by Coldjensens
Setting aside the idea of keeping your tank half full, it seems odd the car makers are basically tricking people into carrying around 3 gallons of gasoline they they will never use, or at least which the car mfgs want to make sure they never use. This is apparently to ensure there is always 3 or more gallons of gasoline in the car to keep the internal fuel pump cool.
They do use it. And in an emergency you can run it on down. But for every day normal driving habits a lot of people are lazy. The risk of burning up pumps under warranty from neglecting to keep the tank full is high enough that the manufacturer built in a safety net that most don't realize. It keeps you from trying to run it to empty or burning up the fuel pump.
Quote:
Originally Posted by Coldjensens
It is interesting to me that manufacturers spend huge amounts of money and take risks to make parts that weigh a few ounces less, yet they encourage you to carry around several pounds (18) of excess fuel. Why not go back to the older, slightly heavier, fuel pumps and provide smaller gas tanks with a smaller or no hidden reserve. That would shave off more weight then many of the things they spend so much money on and end up with chintzy parts or parts that are crazy expensive to replace in order to cut an ounce or five. (With some vehicles, their extreme efforts to shave off a little weight makes no sense to me at all. I can put hundreds and hundreds of pounds of people or stuff in my truck, and the MPG remains exactly the same. What are they trying to accomplish by using cheaper lighter parts and making my truck 50 or 100 pounds lighter? I can see shaving off a few pounds in say, a Fiesta, might make some difference, but why put in less robust lighter parts in a 5500 pound truck? All that does is make things break more easily, the weight reduction is meaningless)
When your fuel pump was in your trunk or underneath your car and easily accessible, you did not need to carry around 18 or more pounds of extra gasoline to cool it, and you could replace most of them in less than half an hour. Sure the pumps weighed a tiny bit more (a matter of a few ounces), they did not cost more and they did not cost much of anything to replace if they wore out.
Maybe I should tell the car mfgs I found a way for them to shave nearly 18 pounds off every single car and massively reduce repair costs at the same time. Just go back to exterior fuel pumps and make all the gas tanks three gallons smaller.
On older cars, I think I have had maybe two or three fuel pump failures and always at 100K miles or more.
It isn't about weight. It's about reliability. There are a couple of different reasons they stuck pumps in the tank.
Vapor lock - Carbureted engines with external lower pressure pumps can create air bubbles in the lines from heat, causing vapor lock. I've even seen fuel boil and vapor lock an engine. It then has to cool off before it will restart. This happens a lot in carbureted race cars.
Priming - The engine mounted pumps sometimes lose prime between the tank and the pump. Ever notice that older carbureted cars took longer to start sometimes? That was because the system had lost its prime. Some really old cars had hand primer pumps to prime the system before cranking. Since pumps are in the tank, the distance between the fuel and the pump is minimized, so when the key is turned over the pump can quickly prime and ensure the fuel lines are full and at the correct operating PSI. New cars usually start by the second time the engine has turned over.
Higher PSI - Fuel injected systems run at a much higher PSI than carbureted systems. Therefore, the components heat up more. Moving the pump into the tank cools the pump and sends cooler fuel to the engine.
Less strain on the system - Manufacturers determined years ago that it was much easier and more efficient to push fuel from the tank to the engine than to try to pull fuel from the tank.
I'm driving a 2015 Honda Fit. The owner's manual states that the car has an 11.6-gallon tank. Since I started driving about 20 years ago, I've had a practice of filling up the tank a few miles after the gas light turns on.
Being a newer car, the Honda Fit also has a range indicator that counts down the number of miles I can supposedly go. The gas light comes on when it says there is about 40 miles left. I noticed that even as the range indicator approached zero, I was only putting in 8.5 gallons of gas.
I started experimenting with driving the car after the fuel range hit zero, which felt a bit like jumping off a cliff with my eyes closed, despite what I knew about the size of the gas tank. However the wheels kept spinning and I didn't run out of gas.
This morning I hit my record which is 42 miles beyond zero before filling up. But when I stopped for gas I only put 9.5 gallons in the tank. Based on what it says in the owner's manual, there was still two gallons of gas in the tank, which is about 80 miles of driving. That's 120 miles passed the "zero" mark on the range indicator and 160 miles after the gas light comes on.
In my opinion, this is an incredibly excessive amount of caution. When the gas light just means that you are a more than half, but less than 2/3 through your tank, it really stretches the meaning of the indicator. Plus, I prefer to spend as little of my life as possible in gas stations so I'd prefer to drive until almost empty. I've never run out of gas in my life.
Just wondering how this trend started. Was there a rash of drivers going more than 100 miles after the gas light came on and running out of gas despite the warning?
I notice your location is listed as "Liminal Space" - how far apart are gas stations in Liminal Space? In Reality, there are some places where you might have to go quite a distance, and really you need to plan on going further because you might miss an exit or there might be some other emergency. Extra wiggle room on fuel saves the manufacturer money if they offer roadside assistance.
It isn't about weight. It's about reliability. There are a couple of different reasons they stuck pumps in the tank.
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Based on my personal experience I have a hard time accepting that. Prior to the new design I had fuel pump failures rarely and when I did, it took 20 -30 minutes to replace them and cost about $40. The older cars I have with external fuel pumps still cost only about $40 - $60 for the part and replacing them is free because I can DIY in minutes. In one car I can replace the fuel pump in about 5 minutes, as long as I do not have to spend an time looking for my tools.
Now - we have had a failure in most of our newer cars (one twice) and it costs $400, - $500 but if you cut a hole thought the body of your car to get at it, you can get it done for $250 or so. To DIY, you are looking at having your car down for a couple of weekends, or at least one weekend. In one car, you had to disassemble the exhaust drop the tank and then have the exhaust welded back together (that was the first car I had them just cut a hole through the body to get at it).
I have only seen one of these new pumps. I asked for the part when they replaced it and took it apart to see why it failed. It was obviously cheaply made, mostly plastic parts. Looked like a clock motor from the 1960s. Failure was the motor. Impellers were fine, wiring was fine.
If they were meant to be more reliable, they would not be dependent on carrying around 3 extra gallons of gasoline to cool them. Some people seem to think you need to keep more than the 3 gallon hidden reserve to keep them cool (not sure if there is any merit to this, but even here, people are claiming you need to keep 1/4 tank on top of the 3 gallon reserve. So for me, I need to carry around 10 gallons of gasoline all the time to keep my fuel pump from failing? That is not more reliable.
Besides, I can replace 8 - 10 fuel pumps for the cost of one new one. Given the most I have ever had to replace on any car is 2, it does not seem practical to instal pumps that are likely to fail and cost 10 times more to replace.
One other thing with the older pumps, when they started failing, you could usually tap on them and get them to run again for a while. You might have to pull over every five or ten miles and tap some more, but you could get to the car parts place where you could just put a new one in in the parking lot. Now, the car just quits dead. Even if tapping would help, you cannot get to it.
I am having difficulty finding anything about this design that is better. More expensive, higher failure rate, absurd access. Maybe there is a safety advantage. At least over the trunk mounted ones. If your hoses fail, you cna end up spraying gasoline all over your trunk and then igniting it with the brake lights or turn signals. I have never heard of this happening, but it is conceptually possible.
There must be some reason they did it. It is rare they do something just plain stupid (sometimes they do, sometimes someone's brother in law owns a third tier who came up with a stupid idea and they cannot sell it so executive orders the company to design the stupid part into vehicles. That is rare, but it does happen.) I doubt this is what happened here because they all do it now it seems.
I asked a friend of mine who works in Design and development about this, and he just chuckled and said it is really stupid. Now, he designs transmissions, not fuel pumps, so maybe he just does not know, but they tend to know about each others areas. They hang out and discuss this s&^$, which can make them really boring at parties, but great to know if you want an answer to something like this (usually).
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will be struggling to keep cool as it uses the gas to prevent overheating expect a in tank fuel pump replacement in the near future OP
It sounds like you had just enough fuel in the lines for the engine to run long enough to eventually purge the air out on its own. If you run it until the engine dies before switching I'd be shocked if it started back on its own without some help. This is very hard on a diesel engine.....
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No $300 In Tank Fuel pumps. Fortunately VW's that I work on (up to 1999.5) have a very simple access port to swap out in-tank fuel pumps. 10 min, vs 10 hrs on a USA car / van / pickup truck + the danger / hassle of draining the fuel tank. 
