quote:

Originally posted by Chowser:
I have heard the it keeps the fuel pump cool stuff but I have it ingrained in myself and my kids to never let it get below 1/4 full because you never know what you're going to run into and you might run out of fuel. I have been stuck in traffic for over 4 hours because of some serious crash. Like near those tunnels that go through the mountain in VA?

During the winter times, my kids and go I fuel up at 1/2 tank.

On long trips, a full tank will get my around 550+ miles so I think I've driven long enough before empty to stop and refuel and take a break. Like when my son was stationed at Fort Bragg, I could make it there in one tank (it was about 510 miles away) and we've done it in one drive but I'd rather stop and take a break and fuel up at least halfway.

I have a brother from another mother that lives in SW VA,
we have traveled 77, from 84 up into WVA,

2 tunnels, seems always an accident or construction
and not much for a gas stop,

he calls the area between the tunnels The Land that Time Forgot,

quote:

Originally posted by lyman:

quote:

Originally posted by 12131:
Soooooo……………I guess it’s both fact and myth. Fascinating.

maybe a mythical fact?? or a factual myth?

Ask Dan Rather.

quote:

Originally posted by lyman:
he calls the area between the tunnels The Land that Time Forgot,

It kinda is! And it’s really pretty.

(Note: a good portion of it is a well-known speed trap.)

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Back on topic: I try not to get below a quarter-tank. I tend to run on the “what if someone gets horribly sick in the middle of the night” premise, and wouldn't want to have to stop for fuel on the way to get or give help.

“Be prepared.”

I don't know about the whole fuel pump business, but back in the 70s the reason for not letting it run low was more condensation in the winter in the fuel tank. Pumps were not in the tank back then. Don't know if that was really an issue but I still never let my tank get below 1/4 full.

In my Volvo S60, NOT allowing your tank to dip below quarter full adds a second fuel stop to a 675 mile trip. More significantly, it adds a fuel stop to a 340 mile trip when there might be no reason to stop otherwise! Both of those fuel stops are completely unnecessary based on the range of that vehicle...Ain't nobody got time for that!

I can’t speak to the question of whether it’s fact or myth, but I seldom let my tanks get below 1/2, and I start to get REALLY antsy if they get down to a 1/4, especially on a road trip. My truck is a 2022 GMC 2500 HD with a 36 gal tank, so I top it off when it gets down to 3/4 full because it’s less shocking with current fuel prices. (Yes, I know I’m spending the same amount over time whether I fill it at 3/4 or 1/4, but it “feels” less painful when the bill that day is less.)

My daughter, on the other hand, sees her low fuel light frequently even though I raised her NOT to do that. I’m not sure I’ve ever the low fuel light on my truck. I saw the light come on once on my wife’s car on a road trip and I was panicking. I had decided to pass up a gas station thinking there would be another soon and I was sadly mistaken…

I always prefer to keep the tanks full in case of any need to bug out or just travel on a whim. If it’s better for the fuel pump, great: if not, it’s better for my peace of mind.

Besides, as I’ve gotten older I need to stop and stretch more often, and the wife has to pit stop more frequently.

No if you drive a Yaris, Chevelle or Terrain.

Yes if you have a Buick Grand National.

F^#)* yeah (!) if you have Mercedes Benz 300 turbodiesel.

quote:

Originally posted by

In my Volvo S60, NOT allowing your tank to dip below quarter full adds a second fuel stop to a 675 mile trip. More significantly, it adds a fuel stop to a 340 mile trip when there might be no reason to stop otherwise! Both of those fuel stops are completely unnecessary based on the range of that vehicle...Ain't nobody got time for that!

No way in the world at my age I can go for 340 miles without stopping to take a piss and stretch my legs. I got time for it.

I suspect that like most “old wive’s tales” there may have been some reality with some models during some period of time. I’ve never seen it.

The only fuel pump I’ve ever replaced was the one on the block of the 327 in my 1969 Chevy El Camino. It’s starting to leak in the middle of a shift delivering for Dominoes while I was in college was what made me realize that part of my income from that job was converting my vehicle into cash. I’ve always wondered if Uber and Lyft drivers have made the same connection…

The rule in our household about not going below a quarter tank originally came from the time very early in our marriage when we passed up the opportunity to get gas on the way to phoenix at night and while we didn’t run out, the stress level was uncomfortably high for uncomfortably long before we got another opportunity and filled up. Since then, another reason has occurred. If we need to go somewhere, not having to fill up first saves time. In normal life that is a convenience. In an emergency, filling up may not be an option. Another way to think about it is that an empty car is about as useful as an unloaded gun. Why put yourself in that position?

I am not a mechanic so no clue, but interesting question. My truck is 24 years old and still runs great. Usually once it is at a quarter tank once a month, I add Chevron Techron High Milage additive and dive it as close to empty as I can. I didn’t start doing that until about 5 years ago and I noticed a huge improvement in my engine with no knocking and no smoke out of my exhaust when I punched the gas pedal while driving.

I change my fuel filter regularly. I need to replace my fuel pump and will do it once the weather gets a little cooler so that will let me examine my fuel pump and look inside fuel tank. Overall I would think it does not matter.

Whether fact or fiction, I have followed my dad’s advice to not fill up my vehicle with gas if I see gas being delivered to the gas station at that time. My dad said it stirs up all the sediment in the storage tanks and then that goes into your gas tank if you fill up at that time. Again though, I just make sure to regularly change my fuel filter like any other filter.

My only knowledge is 90's Chevy trucks and suv's. Fuel pumps will go out if you consistently go below 1/3 of a tank or less. That much I do know.

Had a Levi Package Jeep CJ5 with the slant 6. Gas gage was inop so I used to fill by the odometer. Can't tell you now how much it took as I never ran it past 200 miles with filling it up. YMMV

In the ancient of days, the fuel tank was a source of fuel to the mechanical fuel pump located on the engine. All pumps require a wet inlet, and so remain able to provide suction (or "lift") from a source. A nearly empty fuel tank has very little fluid dynamics pressure, and getting the fuel from the rear of the car to the pump on the engine became an issue as the tank level dropped below some level. "Priming the pump" is the phrase describing how liquid is brought into the pump body so it can be increased in pressure. Fuel tank level in carbureted engine days was important. The pump, typically on the side of the engine, actuated by a lever follower on a camshaft lobe driven by the crankshaft, had a rubber diaphragm to separate the air side from the fuel side. This, you will remember, was after fuel tanks were placed in the frame rails, decades ago, up to the 1980s. Nearly fifty years ago.

One thread on this forum recently raised the concern about a fuel sending unit hanging up after the OP let the fuel go quite low. He was able to undo the float by driving at steep angles. So, we have some evidence that letting the tank become nearly empty can be harmful, to its operation, but NOT to the in-tank pump. The OP reports NO fuel pump issues after resetting the float.

But, for pump-in-tank cars, which is nearly all of them since PFI became normal, fuel pump concerns are most often related to lack of use, gelling of fuel, rust in a tank (above the fuel level, the tank can rust).

Remember also that today, we have transitioned from PFI to GDI or dual-injection engines. PFI pumps are around 60 psig to the injectors. GDI pumps ... that's another story. These are actually mechanically-driven by the camshaft, and are located underhood. Yep, nowhere near the fuel tank. Or fuel. The in-tank pump is merely a "lift pump" with sufficient pressure to move fuel to the high pressure pump in the engine compartment. Obviously, the in-tank fuel level has NOTHING to do with those high-pressure pumps living forever.

And, the high-pressure pumps are quite mechanical. A cam lobe (or three) pushes the pump follower up and down. The incoming fuel is pressurized up to 3000 psig, as required. There are recirculation paths, springs, relief passages, etc. in the pump itself. Believe it or not, high pressure fuel pump wear is imperceptible, over hundreds of thousands of operating cycles. Yes, I have tried to measure it. Yes, with really expensive measurement devices, capable of discerning millionths of a meter (microns). No wear.

So, what kills in-tank pumps? Debris. Rust. Gelation. Neglect, in other words. They are, however, remarkably tolerant devices.