Re: Repeatedly Running On A Low Tank?
 

On Jun 2, 6:34 am, Bill Putney <b...@kinez.net> wrote:
>
> 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.
> ...
> If anyone wants to argue this, be sure of your facts beforehand - I used
> to design automotive fuel pump components.
>

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.

Re: Repeatedly Running On A Low Tank?
 

Elle wrote:
> "Bill Putney" <bptn@kinez.net> wrote
>
>>*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).
>
>
> "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.
>
>

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.

Re: Repeatedly Running On A Low Tank?
 

Elle wrote:

> "rigger" <dgrup@aol.com> wrote
> On Jun 2, 8:05 am, "Elle" <honda.lion...@spamnocox.net>
> wrote:
>
>>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.
>
> snip
>
>
>>>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.
>
>
> 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.
>
>

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

Re: Repeatedly Running On A Low Tank?
 

The Reverend Natural Light turned on the Etch-A-Sketch and wrote:

> On Jun 2, 6:34 am, Bill Putney <b...@kinez.net> wrote:
>>
>> 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.
>> ...
>> If anyone wants to argue this, be sure of your facts beforehand - I used
>> to design automotive fuel pump components.
>>
>
> 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.

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. :P


--
www.perfectreign.com || www.filesite.org

powered by the lizard: www.opensuse.org

Re: Repeatedly Running On A Low Tank?
 

"mjc13<REMOVETHIS> @verizon.net>" <"mjc13<REMOVETHIS> Elle
wrote:
>> I do not want your speculation. I am well experienced in
>> pump design myself. I want facts from a study of pump
>> failure.
>
> 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.

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.

Re: Repeatedly Running On A Low Tank?
 

Bill Putney <bptn@kinez.net> wrote in
news:6ai0kvF37k2jlU1@mid.individual.net:

> Don't Taze Me, Bro! wrote:
>> 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.
>
> 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')


I realize all I have is antidotal evidence, but in 95% of the pumps I
replace, I always ask the customer and it is almost always the ones I am
replacing admit to running the tank low most of the time. KB

--
THUNDERSNAKE #9

Protect your rights or "Lose" them
The 2nd Admendment guarantees the others

Re: Repeatedly Running On A Low Tank?
 

When my Civic tank is low, it takes a lot longer to start. I've read
different theories on why. One is that a one-way valve on the fuel
pump seals better when it is lubricated by fuel, so gas stays in the
line. Whatever the reason, keeping the tank full puts less stress on
the battery, fuel pump, and starter.

Re: Repeatedly Running On A Low Tank?
 

I have noticed a slight delay in starting when the tank is
low (say 1/8 tank and less) on my 91 Civic as well.

"DIYBOI" <rbrailas@courts.state.tx.us> wrote
> When my Civic tank is low, it takes a lot longer to start.
> I've read
> different theories on why. One is that a one-way valve on
> the fuel
> pump seals better when it is lubricated by fuel, so gas
> stays in the
> line. Whatever the reason, keeping the tank full puts
> less stress on
> the battery, fuel pump, and starter.

Re: Repeatedly Running On A Low Tank?
 

mjc13<REMOVETHIS> wrote:
> Don't Taze Me, Bro! wrote:
>
>> 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...

Same here. My daily driver Chrysler Concorde just turned 200k miles
last week from its 80 mile/day commute. I run it as low as I can
before filling up each time at the filling station across the street
from my house - typically with the gage anywhere from 3/16 tank to below
'E'. Original fuel pump.

> 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.

The Chrysler LH car fuel filter is built into the sender/pump/regulator
assembly - tank would have to be dropped to replace it. But they are
designed to last longer than the vehicle (barring getting some really
bad/dirty gas) - no replacement interval specified - and judging from
the total lack of fuel filter problems mentioned on the forums, they did
a good job on the design.

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

Re: Repeatedly Running On A Low Tank?
 

Elmo P. Shagnasty wrote:
> In article <%HP0k.6360$%Z1.4068@trnddc05>,
> "Don't Taze Me, Bro!" <N00One187@NoWhere.Com> wrote:
>
>> 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.
>
> 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.

Far be it from me to criticize Fox News, but in this case I agree with
you. I find *all* news outlets to be totally FOS when they try to
discuss technical subjects.

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

Re: Repeatedly Running On A Low Tank?
 

hachiroku wrote:
> On Mon, 02 Jun 2008 05:53:18 -0700, jim beam wrote:
>
>>> 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?
>> 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.

The overwhelming majority of the cooling (and *all* of the lubrication)
of the pump and its internal components comes from the constant flow of
fuel thru the pump and around each component. Very little cooling comes
from the mostly stangant fuel surrounding the pump.

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

Re: Repeatedly Running On A Low Tank?
 

hachiroku wrote:
> On Mon, 02 Jun 2008 06:44:48 -0400, Elmo P. Shagnasty wrote:
>
>> In article <%HP0k.6360$%Z1.4068@trnddc05>,
>> "Don't Taze Me, Bro!" <N00One187@NoWhere.Com> wrote:
>>
>>> 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.
>> Um, no it won't.
>
>
> The pump is cooled by the fuel in the tank. You want to keep in enough to
> cover the pump.

Almost all cooling of the pump comes from fuel flowing thru it - very
little from mostly stagnant fuel around the outside of the pump.

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

Re: Repeatedly Running On A Low Tank?
 

Elle wrote:
> "Bill Putney" <bptn@kinez.net> wrote
>> *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).
>
> "most"? I would think you would want to err on the side of
> safety and not inconveniencing a driver with a sudden pump
> breakdown.

The designs are not that thermally marginal to worry about. I am being
facetious when I say you should only drive your car in the rain to
maximize cooling of your tires, but it illustrates my point that it
isn't worth worrying about.

> 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.

I can't argue with that.

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

Not in today's sealed (and sometimes plastic) tanks.

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

Wear of the bearings (which for most pumps are actually plastic holes in
pump/motor end caps (basically, plastic bushings) and wear of the brushes.

Usually the plastic end caps (that act as the bearings for the armature
shaft) are glass filled. The molded bearing (bushing) surfaces have a
microscopically thin film of plastic separating the glass fibers from
the metal shaft - an inherent result of the molding process of
glass-filled plastics. Once that thin film wears thru, the very
abrasive glass wears the metal shaft faster than the plastic itself
wears believe it or not (I learned this when I worked as a
designer/engineer/manager for a supplier of fuel pump parts to GM/Delphi
and Ford/Visteon. Once there is significant play between the shaft and
the bearings/bushings, the armature literally rattles around and
eventually crashes into the magnets (also the pumping section is mounted
on the shaft, so its close-clearance parts start rubbing against/hitting
each other, depending somewhat on the type of pumping section - gerotor,
turbine, moving vane, etc.).

Sulfur in fuel of third world countries is a big corrosion problem for
fuel pumps.

Presence of silicone compounds greatly shortens brush life.

The interconnecting wires can break from vibration - like if they have a
nick, and the car goes over a railroad track often - vibration and the
notch effect don't go well together.

IIRC, brush compounds have to be specifically designed to handle large
concentrations of ethanol (I may not be 100% correct on this point -
been out of that field for 7 years)).

I do know that sometimes metal film plastic capacitors (for EMI
suppression) will be destroyed by alcohol in the fuel (alcohol molecules
are so small, you can't keep them from leaching onto the capacitor and
etching away the metal film. When that happens, the capacitor is no
longer a capacitor - EMI problems).

I'd say the shaft/bushing wear is the biggest common cause of failure
(intermittent) - it's why a pump in the process of failing can often can
be heard rattling. Next would be worn out brushes - also intermittent
(temperature- and shock/vibration-dependent), but noiseless, but brushes
are usually over-designed as far as life (length).

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

Perhaps I shed some light for you with some of my comments. Certainly I
do not have anywhere near exhaustive knowledge of the subject.

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

Re: Repeatedly Running On A Low Tank?
 

ToMh wrote:
> On Jun 2, 2:12 am, "Don't Taze Me, Bro!" <N00One...@NoWhere.Com>
> wrote:
>> 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.
>
> 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.

No. There are no dynamic seals in fuel pumps like in a typical
automotive water pump. Running dry (not a credible situation in
general) would not affect case seals (which are static crimped seals).

> 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...

Not likely since the pumping section is at the bottom of the pump, so
when you "run out of gas", there is a column of fuel extending from the
pumping section of the pump (at its very bottom), thru the pump, all the
way to the fuel rail and injectors. Granted that column of fuel is not
moving, but it's there nonetheless. And the engine dies, and the
computer turns the pump off in a matter of seconds. No real chance for
significant damage from heat or lack of lubrication.

> Just having a low
> tank, without the pump running dry, can't possibly cause any
> problems.

I'll buy that.

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

Re: Repeatedly Running On A Low Tank?
 

Retired VIP wrote:
> On Mon, 2 Jun 2008 09:26:47 -0700 (PDT), ToMh <tlhumm@hotmail.com>
> wrote:
>
>> On Jun 2, 2:12 am, "Don't Taze Me, Bro!" <N00One...@NoWhere.Com>
>> wrote:
>>> 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.
>> 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.
>
> 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?

The pump will never not see fuel inside. The pumping section is at the
very bottom of the pump, so the column of fuel will be "dancing" on the
pumping element (think of a turbine blade). The only part (in an empty
tank) filled with air will be the pickup tube.

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