Repeatedly Running On A Low Tank?

Consider filling up your tank and not letting it drop below halfway, instead
of keeping it on low and only putting in 2 gallons here and there...

http://www.foxnews.com/story/0,2933,361347,00.html

Not because you could run out of gas and get stranded but because repeatedly
running on low tends to ruin the fuel pump.

 

While Fox "News" might on occasion slip and let a fact slip through
their filters, I wouldn't count on it. We've been running our cars down
to 1/4 or even 1/8 of a tank on a regular basis for 25 years, and have
never had a fuel pump fail. I just sold my 1986 Civic Si with the
original pump. It's much more important to replace the fuel filter at
the recommended interval.

 

I see that thing about running low on fuel damaging fuel pumps posted
all over the internet, but personally I think that's total b.s.

All the critical parts in the fuel pump - bearings (bushings), armature,
brushes/commutator, pumping elements (vanes, rotors, or rollers) - are
constantly bathed in the fuel as it flows thru the pump. That
lubricates and cools the parts regardless of fuel level in the tank.

With regulator bypass pumping/circulation that modern cars have, there
is full volume of fuel going thru the pump at all times it is running
regardless of engine demand. The only effect of low fuel in the tank is
a slight temperature rise of the volume of fuel in the tank (due to same
electrical power dissipated in the pump being absorbed by less mass of
fuel), and that rise will be very small - power used by fuel pump is
small - temperature rise of the fuel in the tank and the tank itself
will be very small - lots of mass compared to the power being dissipated.

*BUT* - again - the fuel is constantly flowing thru and around all
internal components of the pump whenever it is running providing cooling
(unless you actually run out and the engine stops - but that is a
different scenario altogether, and even then, the pump will still be
full of fuel at that point with a full column of fuel from its lowest
end to the fuel rail - only the pickup will be filled with air, and
there won't be any flow - and most cars turn the pump off when the
computer senses that the engine is no longer running).

If anyone wants to argue this, be sure of your facts beforehand - I used
to design automotive fuel pump components.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

Um, no it won't.

Interesting that the article just threw that out there with no further
explanation. But then, that's Fox News for you.

 

It's like every "factual" story in the media is just all spin. So, is this
guy an Oil Company shill trying to get us to fill-up and inflate the price
of gasoline? A futures trader? A tow-truck operator? An idiot? It could be
anything but the truth. There is so much unadulterated BS in the media, from
NAFTA Superhighways to infomercials for Jack LaLanne Juicers. The Reader's
Digest used to be the main source of of this righteous nonsense (That's
Outrageous!) but now it is everywhere. Do you awaken with a painful need to
urinate? You need a new drug! Do your too-small briefs leave red marks on
your skin? It's cancer! My favorites are the ads for Lunesta: Side effects
many include drowsiness! WTF? Sorry for the rant...........

 

no, that could /never/ happen. not ever. not in a million bajillion
years. no sir.

oh, wait, the fuel pump thing is utter bullshit, so...

 

Once again you show how little you know.

The fuel pump is cooled by fuel. If you run on a low tank that doesn't
cover the fuel pump, it can fail prematurely. At $190~425 for a fuel pump.
it's probably cheaper to keep enough fuel in the tank to cool the pump.

What did I expect from someone who changes his oil at 12,000 miles whether
it needs it or not.

Reply when you get a clue...

 

The pump is cooled by the fuel in the tank. You want to keep in enough to
cover the pump.

 

"most"? I would think you would want to err on the side of
safety and not inconveniencing a driver with a sudden pump
breakdown.

Barring presentation of a study showing no detrimental
effects of either regularly running on a very low tank or
running to empty, I think not doing these things is easy
enough and indeed an investment that costs one only a litle
extra time getting gas over the life of the car. If possibly
burdening the pump by forcing it to move air is not really a
problem, then I remain concerned about dirt in the bottom of
the tank clogging the filter and lines downstream of the
pump prematurely, or possibly wearing mechanical parts on
the pump, causing the pump to have to work harder, meaning
it draws more current, aging electrical parts more quickly,
etc.

Does rust accumulate in fuel tanks? If so, does running it
near empty hasten the buildup of rust?

What are the leading causes of fuel pump failure? If it's
"age," what exactly causes aging to accelerate?

I do not want your speculation. I am well experienced in
pump design myself. I want facts from a study of pump
failure.

 

If you don't mind me breaking in to ask a question?

How hot would the fuel need to become in order to
accelerate the breakdown of the materials used in
the fuel pumps you're familiar with? In my mind I
can't imagine most materials responding in a neg-
ative manner unless temperatures reach very high
levels (over 200 deg. F?) as I'd imagine they are
chosen for temperature resistance, among other
things.

dennis
in nca

 

The fuel pump is like any other fluid pump. it requires the liquid
running through it to lubricate and cool it. If you run a pump dry,
its seals can burn out fast. But as long as there is fluid running
through it, it will be fine. So as long as there is gas running
through the pump, it won't get damaged, but I could certainly see how
it could be damaged if you let it run out of gas. Just having a low
tank, without the pump running dry, can't possibly cause any
problems.

 

can't imagine most materials responding in a neg-
ative manner unless temperatures reach very high
levels (over 200 deg. F?) as I'd imagine they are
chosen for temperature resistance, among other
things.


I agree. I would not expect an increased fuel temperature
(due, say, to the pump recircing from a low fuel tank) will
have a noticeable effect on pump part wear, one because I
do not expect the temperature increase to be much (as Bill
indicated) and two because I think the materials are durable
enough, as you wrote.

I am also concerned about how the fuel's sloshing,
particularly when the vehicle is turning, could tend to
starve the pump, making it work harder blah blah. Granted
this would have to be at very low levels. The sloshing is
certainly enough that I see my 91 Civic's fuel gage go lower
on left turns; higher on right turns; when the gage reads
below about 1/3 tank.

Way too much argues against driving to or near an empty
tank.

I am speaking of electric fuel pumps, by the way, which are
what are used on cars with fuel injection. So anyone having
an older, carbureted car likely has a mechanical fuel pump
and will have somewhat different concerns.

 

Hmmm.....What if the pump was getting gulps of air due to the gas
sloshing around in a nearly empty tank? Is the pump pickup located in
a well or a low point in the tank?

Jack

 

Sorry to burst your bubble hachi but the level of fuel outside the pump
means nothing. As has been mentioned before the fuel being pumped goes
directly through the motor assembly on its way from one end of the pump to
the other. This means the armature, commutator, brushes, and field magnets
are all constantly bathed in flowing fuel while the pump is on. Typical
construction is a steel tube containing the magnets which is crimped onto 2
end caps. The bottom end cap contains the turbine (TBI) or gerotor (MPI)
pump and the top cap contains the fuel outlet, check valve, electrical
terminals, and brush holders. The pressure relief valve that protects the
pump from being dead-headed from a plugged filter or a kinked fuel line is
also in one of the 2 caps. I have also seen pumps that were all plastic. I
haven't designed pumps but I have taken apart a half dozen failed ones.

All that being said I have also personally heard the distinct sound of vapor
bubbles going through the fuel pressure regulator on a car with the engine
running. I think in some cases the pump starts sucking air through the top
of the pickup sock before the tank is completely empty but yet is still able
to supply enough pressure and volume for the engine to run.


P.S. Why is this cross posted to about a zillion newsgroups?

 

If it's getting gulps of air then that would be a problem, but the OP
was talking about 1/4 tank!.

 

GM TPI has the regulator on the outlet side of the fuel rails. Fuel
returning to the tank has run all the way through the rails - which
are bolted to the intake manifold. With the engine hot, you can grab
the fuel rails and they'll be cold.

I'll bet that makes a substantial rise in temperature inside the tank
on low level. Who knows what affect that has on pump life.

 

It isn't a study, but my post about my experiences involves quite a
few cars over several decades, and one car for 22 years. It also
includes another car over 9 years. I stand by what I wrote.

 

Just to be clear: the cars I mentioned all have/had electric fuel pumps.

 

Good point - Why doesn't someone buy me a new top of the line truck, and
I'll test it out for y'all.

No charge for the test.

 

Well I happen to think anecdotal experiences in certain
areas, like this one, count for a lot as "data." I think
maybe we can further observe that we just do not see many
fuel pump failure reports here, for one. They certainly do
happen, but not that often. Many factors must go into what
determines fuel pump life. Maybe 1/8 tank and more is just
not going to burden the pump in any significant way. Maybe
the climate makes a big difference in fuel pump rate
failure. E.g. climates that have a lot moisture in the air
will tend to promote more rust in the fuel tank than if the
climate were dry. Maybe some pump manufacturers go cheap on
parts, so a chip of rust passing through the pump means it's
more likely to cause the pump to fail.

From talk on the net, it does seem to me that debris
accumulating at the bottom of fuel tanks is not uncommon.
And why have a fuel filter whose changing is prescribed to
be every few years, besides, if the debris is no concern? So
too do we see reports of fuel tanks failing.

I do not think the OP's article is baloney. It's just
suggested best operating practices to minimize fuel system
problems, ISTM. Not a big deal.