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E39 (1997 - 2003)
The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

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  #1  
Old 05-16-2011, 10:44 PM
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bluebee bluebee is offline
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How much fuel does it take to 'cover' (i.e., cool) the BMW E39 electric fuel pump?

I'm both skeptical and confused about the 'requirement' to keep the electric fuel pump in the E39 covered in (cooling) fuel at all times.
  • Skeptical:
    • Did the BMW engineers really design a pump that 'could' operate at levels of fuel that will actually damage it ...
  • Confused:
    • If so ... then what would a chronically overheated pump look like in an autopsy?
So, to better understand this oft-stated need, let's see if we can ascertain exactly how much fuel it actually takes to 'just' cover the fuel pump in that wonderfully cooling benzene-based elixir ... and/or ... let's ascertain (with pictures) what actually happens to a reputed overheated fuel pump.

As usual, I'll embarrass myself with an initial stab but I'm hoping someone actually knows the answer and therefore dutifully raises the knowledge level of the tribe for the benefit of all (true socialism at work).

According to a blurb in the BMW TIS 16 00 005 kindly supplied by QSilver7 here:
- How to siphon gasoline out of the E39 into a gas can

Quote:
The electric fuel pump must not operate without fuel! After completing repairs and before starting engine for first time, fill fuel tank through fuel filler pipe with min. 5 ltr. fuel.
So, my first 'guess' is that it takes 1.3 US gallons (i.e., 5 liters) to 'just cover' the electric fuel pump.

Given a nominal 18.5 US gallon tank (70 liters) based on this thread:
- Are all E39s 18 gallons of fuel?

Quote:
  • 70 liters total fuel in all the E39s (18.5 gallons, although you can stuff in a gallon more)
  • Yellow light indicates you're at the model-dependent fuel-reserve level:
    • 525i = 2.0 gallons of reserve
    • 528i = 2.1 gallons of reserve
    • 530i = 2.0 gallons of reserve
    • 540i = 2.5 or 2.6 gallons of reserve
  • Gong goes off at approximately 31 remaining miles (???)
  • Double dash shows up at ??? remaining miles (it's not zero 'cuz I've driven at least five or ten miles on the double dash rather often)
If the gong goes off at 31 miles, isn't that just about 1.3 gallons (or so)?

So, my very tentative (and not at all sure) conclusion, at the moment, is the gong tells you that your fuel pump is starting to NOT be covered in the cooling elixir.

But I have no idea (really) ... so I am wont to ask ...

Q: Anyone have a better idea as to when exactly the fuel pump starts to be NOT covered in fuel?

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Last edited by bluebee; 05-17-2011 at 06:54 AM.
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  #2  
Old 05-16-2011, 10:47 PM
dvsgene dvsgene is offline
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I don't think it is a matter of being COVERED but partially submerged to allow for fuel to cool it and not ingest any air.
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  #3  
Old 05-16-2011, 11:12 PM
edjack edjack is offline
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bluebee,

Don't overanalyze this. Fill up at 1/4 tank.

Or, do your own experiment: run the tank consistently to the red light. Let us know how long your pump lasts as a result.
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  #4  
Old 05-16-2011, 11:44 PM
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bluebee bluebee is offline
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Quote:
Originally Posted by edjack View Post
Don't overanalyze this. Fill up at 1/4 tank.
With all due respect, a LOT of incorrect BMW urban legends exist solely because most people simply don't analyze.

I like to 'know' the answer. Not guess at the answer. That's all.

For example, many people believe the following "BMW lore":
  • Brake vibration is caused by rotors warping
  • The DICE Silverline will charge a dead iPod's battery
  • You must remove the subframe to replace the I6 oil-pan gasket
  • You must use the blue BMW coolant
  • The purpose of alignment sandbags is for camber
  • You must recode the VIN into a used ABS control module
  • You can't change just the pulley on the mechanical tensioners
  • You can't buy the lower radiator hose thermoswitch o-ring from BMW
  • You can't buy the M54 DISA o-rings
  • BMW P1xxx diagnostic codes are the same for all models
  • You can buy Axxis pads in the USA for the front axle on the E39
  • A CAI will increase your horsepower
  • The fancy testers can tell you whats wrong with your ABS
  • Severe shudder upon low speed bumpy braking is due to the ABS
  • You can't remove the radiator nipple without destroying it
  • You must use LL-01 motor oil or your engine will prematurely die
  • You can't remove the screen filter in the power steering reservoir
  • You can't fix your PBT headlight adjusters for $2.50 per headlight
  • You can't use 87AKI Costco fuel for ten years or your engine will prematurely die (this test is still in progress)
  • You must replace the rotors on every pad change
  • Nitrogen in your tires won't leak out
  • etc. (I could go on for a looong while on this)
All of those statements above are, for some people, gospel.

But all are untrue (in the strict sense ... although there is always a shred of truth in all fallacy).

Quote:
Originally Posted by edjack View Post
do your own experiment: run the tank consistently to the red light. Let us know how long your pump lasts as a result.
I've been running that experiment for over a dozen years so far (multiple vehicles), and have yet to replace a fuel pump (as noted in this recent post).

But that isn't the point because a study of one isn't a study at all.

Everyone 'says' running the fuel low will overheat your fuel pump ... and well ... that may be true; but that's not actually meaningful unless we have data that proves either way the truth.

What's wrong with searching for the actual truth anyway?

Autopsy pictures by Flybot:
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Last edited by bluebee; 05-17-2011 at 07:09 AM.
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  #5  
Old 05-17-2011, 12:04 AM
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bluebee bluebee is offline
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Quote:
Originally Posted by dvsgene View Post
I don't think it is a matter of being COVERED but partially submerged to allow for fuel to cool it and not ingest any air.
Interesting. But how 'partial' is partial.

If we answer the question of 'fully submerged', we'll be a long way toward the (real) minimum level that is often recommended.

Googling, I found this 3-series reference which implies 2 gallons is the amount to cover the fuel pump (more or less) in the 3 series BMW.
- Doug's BMW 328is DIY Fuel Pump / Suction Unit Replacement

Quote:
This procedure must be done with less than approximately 7/8 fuel remaining because the tank is sloped slightly. Otherwise, gas will pour out of the opening when you remove the pump / sender units. The best thing to do is what my technician recommended -- run the car down until the gas warning light is on. That represents around 2 gallons remaining (vapor, essentially).
Picture by Doug:


I looked in all the E39 fuel pump R&R guides and nobody listed the actual figures for how much fuel partially (or fully) submerges the fuel pump:
- Testing (1) and replacing the fuel pump (1) (2) () (4) (5) & your available fuelpump options (1) & a DIY for replacing the fuel filter (1) (2) (3) (4) (5) (6)

But, this statement by flybot was telling:
Quote:
Originally Posted by Flybot View Post
I did an autopsy on my dead pump a while back. Here is the link to it (with pics): http://www.m5board.com/vbulletin/e39...opsy-pics.html

Its not worth rebuilding a pump. The other pics of E39 pumps that Ive seen show the same condition: worn out brushes and/or comutator (?) contact area.
Think about that!

If it's true that the common failure is 'worn out brushes and/or commutator', then the question would logically be:

Q: How could 'not' submerging the fuel pump in gasoline cause worn out brushes?

Picture by Flybot:
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Last edited by bluebee; 05-17-2011 at 07:07 AM.
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  #6  
Old 05-17-2011, 12:41 AM
Peeplzchamp Peeplzchamp is offline
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I'm no expert on this, but i thought the issue for anything pumping fluid was to keep a consistent flow, so air doesn't enter, and the pump remains 'primed' - therefore not at risk of it burning out.

So perhaps the orange warning light comes on when the pump isn't fully submerged, therefore 'prime' can't be guaranteed through the pump?
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  #7  
Old 05-17-2011, 04:04 AM
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I have heard of and thought about the "fully submerged" issue. It makes no logical sense to me and I log it off as "BMW Lore".

First and foremost, BMW makes no mention of a unique requirement to keep its fuel pump fully submerged at all times to prevent overheat and premature wear.

Second, the pump, to the best of my knowledge, is not some special E39 unique design. It is probably used on several other vehicles, BMW and more. Again, never heard of a "submerged pump" requirement. If that were the case, it would be easier to simply design it into the system- the fuel pickup would just not go below the level of the top of the pump.

Lastly, and more importantly, if fuel cooling is used as an argument for it to be submerged then it fails from the start. The pump has its pickup located on the tank bottom, of course, inside a mesh screen at to lowest part of the tank. Fuel is drawn through the pump, around all the rotating parts, commutator, brushes, etc, and out the top of the pump and into the fuel line. THAT is all the cooling it needs. Its just a small 12V motor. Heat is not that big an issue. Its not some water cooled 440V 200HP monster that makes enough heat to warm a house. If the fuel tank were to run dry and you kept the ignition on for a long time, I suspect the pump might then show some premature wear possibly from lubrication not heat. How many times have you run out of gas? For me, it been decades. 12V pumps run all day long in dry conditions with the same bronze bushings found in our fuel pumps.

The "Keep the tank partially full to save the pump" is pure, unproven, undocumented BS.




.

Last edited by Flybot; 05-17-2011 at 04:10 AM.
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  #8  
Old 05-17-2011, 05:17 AM
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Fudman Fudman is offline
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Quote:
Originally Posted by Flybot View Post
Fuel is drawn through the pump, around all the rotating parts, commutator, brushes, etc, and out the top of the pump and into the fuel line.

The "Keep the tank partially full to save the pump" is pure, unproven, undocumented BS.
.
I believe that 99% of what Flybot stated is correct. While the pump may be immersed (submerged) in the fuel tank during high fuel levels, for most pump designs, the liquid (fuel) is drawn past the pump, which allows the liquid to cool the pump, much like engine coolant passes through the engine. However, the fuel is not drawn through the pump and around the electrical components. That would short the pump out. It is probably drawn around the outside of the pump casing and through the mechanical components (bearings), which indirectly cools the electrical components and lubricates the mechnical components.

Because modern fuel injection utilizes a high pressure system, the old low pressure pumps used in carbeurated engines are no longer used. These newer pumps "work harder" to maintain fuel pressure which is why some level of cooling is required. There are two primary sources of heat in a pump: mechanical friction and electrical load. The fuel simply acts as the liquid medium to remove heat that accumulates within the pump. If your fuel level drops below the intake nozzle, you will: 1) lose your cooling medium, eliminating the means to remove heat, 2) lose lubrication, increasing the heat generated by friction and 3) as friction increases, electrical load rises which increases heat generation further. Eventually the accumulation of heat will cause the pump to seize. Excess heat may also be a cause for faster wear in friction areas (brush commutator contact, bearings, etc.).

Thus the answer to the original question: Anyone have a better idea as to when exactly the fuel pump starts to be NOT covered in fuel? should be (I believe): Whenever the fuel level drops below the intake nozzle of the fuel pump.

Thus, Flybot's last statement above appears to be correct.
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  #9  
Old 05-17-2011, 05:23 AM
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"Fudman: While the pump may be immersed (submerged) in the fuel tank during high fuel levels, for most pump designs, the liquid (fuel) is drawn past the pump, which allows the liquid to cool the pump, much like engine coolant passes through the engine. However, the fuel is not drawn through the pump and around the electrical components. That would short the pump out. It is probably drawn around the outside of the pump casing and through the mechanical components (bearings), which indirectly cools the electrical components and lubricates the mechnical components. "

Thats incorrect. Ive taken the pump apart myself and I can assure you that fuel is drawn through the pump. http://www.m5board.com/vbulletin/e39...opsy-pics.html. Fuel going through the pump motor is common on cars and vertualy all jet aircraft fuel pumps which are submerged in the fuel. Fuel will not short out the pump.



.

Last edited by Flybot; 05-17-2011 at 05:25 AM.
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  #10  
Old 05-17-2011, 06:11 AM
pshovest pshovest is offline
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Experiment complete.
(1) E28 and (2) E34's with > 175K miles on original fuel pumps, tanks only filled AFTER the red light comes on.

Part 2. Pump doesn't have to be submerged for cooling....you just need enough fuel to allow pumping. Fuel flows directly over the electric motor as it circulates to the FPR and returns to the tank. Yes, the FP motor including the FP motor brushes are flooded by the fuel that CIRCULATES.

Myth debunked. End of discussion.

Paul S
BMW CCA 69606




Quote:
Originally Posted by edjack View Post
.......... , do your own experiment: run the tank consistently to the red light. Let us know how long your pump lasts as a result.

Last edited by pshovest; 05-17-2011 at 06:58 AM.
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Old 05-17-2011, 06:45 AM
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Fudman Fudman is offline
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Quote:
Originally Posted by Flybot View Post
"Fudman: While the pump may be immersed (submerged) in the fuel tank during high fuel levels, for most pump designs, the liquid (fuel) is drawn past the pump, which allows the liquid to cool the pump, much like engine coolant passes through the engine. However, the fuel is not drawn through the pump and around the electrical components. That would short the pump out. It is probably drawn around the outside of the pump casing and through the mechanical components (bearings), which indirectly cools the electrical components and lubricates the mechnical components. "

Thats incorrect. Ive taken the pump apart myself and I can assure you that fuel is drawn through the pump. http://www.m5board.com/vbulletin/e39...opsy-pics.html. Fuel going through the pump motor is common on cars and vertualy all jet aircraft fuel pumps which are submerged in the fuel. Fuel will not short out the pump.



.
Interesting. They don't do that with water pumps. I stand corrected.
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Old 05-17-2011, 07:00 AM
cn90 cn90 is offline
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All fuel pump, whether it is made by Bosch or Pierburg is designed in such a way that fuel is used as lubricant, so yes fuel flows right through electrical connections/stator etc.

To answer bluebee original question, the only way to find out is during fuel pump change (if your fuel pump is bad) make a note how much fuel is needed to fully submerge the fuel pump.

I agree with Fudman, I don't want to overanalyze this thing, just don't let fuel drops below 20-25% level.
At the absolute minimum, keep 15% fuel or 3 gallons in the tank.

The fuel injection era is different from carburetor era.
FI fuel pump needs fuel to cool.
Carburetor fuel pump is mechanical (with diaphragm) does NOT need fuel to cool.
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Old 05-17-2011, 07:27 AM
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bmw_n00b13 bmw_n00b13 is offline
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I had <1L in my tank and the fuel pump started making noticeable noises around that point. FWIW.

Living on the edge!
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  #14  
Old 05-17-2011, 07:34 AM
pshovest pshovest is offline
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Fuel pumps on E12's and E28, very similar to E34 and E39 pumps, were outside the tank so they were never cooled by being submerged.

BMW moved the main pump inside the tanks to eliminate the small in-tank pump the older 3/5/7 series used. 15% or 3 gallons doesn't come close to submerging the pump in an 18 gallon tank. Arguing that submerging pump is beneficial makes no sense. Fuel flows directly over/through/around the heat producing parts of the fuel pump. This design makes submerging the pump completely unnecessary as cooling continues as long as there is fuel to pump. The heat transfer that results from fuel flowing thru the pump is far more effective then simply submerging the pump. This likely explains why these pumps are longlived even when tanks levels are routinely run to the warning light level.

Paul S
BMW CCA 69606


Quote:
Originally Posted by cn90 View Post
All fuel pump, whether it is made by Bosch or Pierburg is designed in such a way that fuel is used as lubricant, so yes fuel flows right through electrical connections/stator etc.

To answer bluebee original question, the only way to find out is during fuel pump change (if your fuel pump is bad) make a note how much fuel is needed to fully submerge the fuel pump.

I agree with Fudman, I don't want to overanalyze this thing, just don't let fuel drops below 20-25% level.
At the absolute minimum, keep 15% fuel or 3 gallons in the tank.

The fuel injection era is different from carburetor era.
FI fuel pump needs fuel to cool.
Carburetor fuel pump is mechanical (with diaphragm) does NOT need fuel to cool.
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Old 05-17-2011, 07:43 AM
cn90 cn90 is offline
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Quote:
Originally Posted by pshovest View Post
Fuel pumps on E12's and E28, very similar to E34 and E39 pumps, were outside the tank so they were never cooled by being submerged.

BMW moved the main pump inside the tanks to eliminate the small in-tank pump the older 3/5/7 series used. 15% or 3 gallons doesn't come close to submerging the pump in an 18 gallon tank. Arguing that submerging pump is beneficial makes no sense. Fuel flows directly over/through/around the heat producing parts of the fuel pump. This design makes submerging the pump completely unnecessary as cooling continues as long as there is fuel to pump. The heat transfer that results from fuel flowing thru the pump is far more effective then simply submerging the pump. This likely explains why these pumps are longlived even when tanks levels are routinely run to the warning light level.

Paul S
BMW CCA 69606
Sorry, I don't know where you get these facts from, all wrong stuff!
Do some more readings.
Get a Bosch Fuel Injection book and read it from cover to cover.
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Old 05-17-2011, 07:49 AM
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Quote:
Originally Posted by pshovest View Post
Fuel pumps on E12's and E28, very similar to E34 and E39 pumps, were outside the tank so they were never cooled by being submerged.

BMW moved the main pump inside the tanks to eliminate the small in-tank pump the older 3/5/7 series used. 15% or 3 gallons doesn't come close to submerging the pump in an 18 gallon tank. Arguing that submerging pump is beneficial makes no sense. Fuel flows directly over/through/around the heat producing parts of the fuel pump. This design makes submerging the pump completely unnecessary as cooling continues as long as there is fuel to pump. The heat transfer that results from fuel flowing thru the pump is far more effective then simply submerging the pump. This likely explains why these pumps are longlived even when tanks levels are routinely run to the warning light level.

Paul S
BMW CCA 69606
Agreed
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Old 05-17-2011, 07:50 AM
cn90 cn90 is offline
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Quote:
Originally Posted by pshovest View Post
....Arguing that submerging pump is beneficial makes no sense. Fuel flows directly over/through/around the heat producing parts of the fuel pump. This design makes submerging the pump completely unnecessary as cooling continues as long as there is fuel to pump. The heat transfer that results from fuel flowing thru the pump is far more effective then simply submerging the pump. This likely explains why these pumps are longlived even when tanks levels are routinely run to the warning light level.
"Warning Level Light" does not mean empty, it still has a few gallons left to cool the pump.

How about an article written by the car guru "Larry Carley":

http://www.counterman.com/Article/84...mp_primer.aspx

Quote:
Originally Posted by Larry Carley
...Electric fuel pumps in late model vehicles work hard and spin continuously as long as the engine is running. Over their lifespan, they will circulate thousands of gallons of fuel. In most fuel injection systems, fuel that is not sprayed through the injectors is re-routed back to the fuel tank. The fuel pressure regulator maintains a certain amount of pressure in the injector supply rail, and routes excess fuel back to the tank through a return line. At idle and low load, therefore, much of the fuel that is pumped to the engine is not needed and is re-routed back to the fuel tank.


This fuel pumpís best days are definitely behind it.
One of the drawbacks of this setup (besides pumping a LOT of fuel unnecessarily) is that the fuel picks up heat as it circulated through the fuel rail on top of the engine. The heat is carried back to the fuel tank, where it may increase the operating temperature of the pump if the fuel level inside the tank is relatively low (say, less than a quarter full). Because of this, the life of the pump can be cut short if a motorist is always driving around with a low tank. Not only does it cause the pump to run hot, but it may also starve the pump for fuel when cornering or braking hard. Thatís not good because a high-speed electric fuel pump requires a steady flow of fuel through it for both cooling and lubrication. Running out of gas is even worse because it runs the pump dry. This can damage the pump or cause it to fail.
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Old 05-17-2011, 08:37 AM
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Flybot Flybot is offline
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Originally Posted by Larry Carley
...Electric fuel pumps in late model vehicles work hard and spin continuously as long as the engine is running. Over their lifespan, they will circulate thousands of gallons of fuel. In most fuel injection systems, fuel that is not sprayed through the injectors is re-routed back to the fuel tank. The fuel pressure regulator maintains a certain amount of pressure in the injector supply rail, and routes excess fuel back to the tank through a return line. At idle and low load, therefore, much of the fuel that is pumped to the engine is not needed and is re-routed back to the fuel tank.

Quote:
This fuel pump's best days are definitely behind it.
One of the drawbacks of this setup (besides pumping a LOT of fuel unnecessarily) is that the fuel picks up heat as it circulated through the fuel rail on top of the engine. The heat is carried back to the fuel tank, where it may increase the operating temperature of the pump if the fuel level inside the tank is relatively low (say, less than a quarter full). Because of this, the life of the pump can be cut short if a motorist is always driving around with a low tank. Not only does it cause the pump to run hot, but it may also starve the pump for fuel when cornering or braking hard. That's not good because a high-speed electric fuel pump requires a steady flow of fuel through it for both cooling and lubrication. Running out of gas is even worse because it runs the pump dry. This can damage the pump or cause it to fail.


This very well may be where this myth originates from. The guy may be be a "guru" but hes not the last word. Im sorry to say it but there is no magic mystical parts in the fuel pump. Its a simple DC electric motor with bushings and a carbon compound brush rubbing on a copper commutator. Common to DC motors throughout the world. Nothing special. His argument that a fuel tank that is low will over heat the pump because of the hot return fuel is laughable. I would challenge anyone to measure, or just feel their low fuel tank after doing some city driving (lots of idle time) and see if it burns their fingers. It will be no where near hot enough to do that. And if its not hot to the touch, do you think its going to affect a metal motor- No. His argument that cornering or breaking hard will cause damage due to fuel starvation is again weak. Ive run my tank down several times (to within 10 miles on the range indicator), and I didnt have any fuel starvation issues, which would show up immeadiatly with stalling, stumbling or hesitation in a high pressure fuel injected system.

Again, this "Keep the tank fully submerged, no lower than X gallons, etc" is pure BS. But whoever wants to worry about it, feel free. Its your car.
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Old 05-17-2011, 08:43 AM
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Quote:
Originally Posted by Flybot View Post
...
Again, this "Keep the tank fully submerged, no lower than X gallons, etc" is pure BS...
I only wish that you have the same experience and wisdom as Larry Carley.

It is NOT BS. It is a fact. The best way to kill a fuel pump is running the tank dry.

I can name you at least 3 cases on my wife's side, it was not me but my brother-in-laws, 3 of them did it (not to mention they get stranded), sure enough they fried their fuel pumps.

This thread is getting to be pointless, first of all, why would anyone in the right mind run the gas tank down to 2 gallons? Exciting?
Nope, it is called stupidity, especially in winter (getting stranded in winter = danger).
In the summer = getting stranded and frying one's fuel pump.
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  #20  
Old 05-17-2011, 08:48 AM
cn90 cn90 is offline
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Quote:
Originally Posted by Flybot View Post
...Again, this "Keep the tank fully submerged, no lower than X gallons, etc" is pure BS. But whoever wants to worry about it, feel free. Its your car.
I strongly recommend that you buy the Bosch Fuel Injection book written by Charles O. Probst. Available on Amazon for $15.
Any serious DIYer should own this book.

http://www.amazon.com/Bosch-Fuel-Inj.../dp/0837603005

This book will open your eyes and you will retract your erroneous statements above.
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  #21  
Old 05-17-2011, 08:53 AM
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Flybot Flybot is offline
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If you are talking about running a tank dry, that is a completely different story. This is about keeping the pump submerged in fuel.

And I guess the engineers at BMW should read that book. They are the ones that designed it.
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  #22  
Old 05-17-2011, 10:55 AM
pshovest pshovest is offline
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Wow...... I leave the room for 3 hours and look at this. Let's get started!!

First you acknowledge my post as facts and then you say they are all wrong. How can facts be wrong?

8683 posts and your best counter to the technical argument I made is to pound the table, beat your chest and declare me wrong. I'm shakin' my boots now! Clearly you don't understand how fuel pumps are cooled or why circulating fuel is more important then submerging the FP.

I own and have read Bosch FI Technical Instructions for K-Jetronic, L-Jetronic and Motronic systems. Several were written well before you were born I suspect. None of them make the bogus claim that emptying tank to reserve light will shorten FP life....which after all is what this thread is about.

I've offered irrefutable evidence of long FP life ((3) BMW's w/ >175k miles) inspite of regularly emptying tank until reserve light is lit. Perhaps you should "Do some more readings" about the importance and making use of empirical data in technical discussions.

Paul S
BMW CCA 69606


Quote:
Originally Posted by cn90 View Post
Sorry, I don't know where you get these facts from, all wrong stuff!
Do some more readings.
Get a Bosch Fuel Injection book and read it from cover to cover.

Last edited by pshovest; 05-17-2011 at 11:11 AM. Reason: spelling
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  #23  
Old 05-17-2011, 11:01 AM
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Jason5driver Jason5driver is offline
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I speak/ write from experience.
Don't run the car with less than a 1/4 tank.
You will burn up the fuel pump.
Also, time/ mileage has a role on the pump as well.
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  #24  
Old 05-17-2011, 11:07 AM
pshovest pshovest is offline
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Start at the top....Warning light level is what this entire thread is about!
So once again you can't offer a technical argument nor can you refute the success I've had with long FP life ((3) BMW's w/ >175k miles) inspite of regularly emptying tank until reserve light is lit.

Your best argument is to offer something you read on the internet? Larry who? Is this Larry the Cable Guy's brother? Can he explain why my fuel pumps last so long
inspite of my intentional fuel pump abuse?

Paul S
BMW CCA 69606


Quote:
Originally Posted by cn90 View Post
"Warning Level Light" does not mean empty, it still has a few gallons left to cool the pump.

How about an article written by the car guru "Larry Carley":

http://www.counterman.com/Article/84...mp_primer.aspx

Last edited by pshovest; 05-17-2011 at 11:09 AM.
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  #25  
Old 05-17-2011, 11:40 AM
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bluebee bluebee is offline
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Quote:
Originally Posted by cn90 View Post
The best way to kill a fuel pump is running the tank dry.
Hi Cam,

The key question at the moment is:

Q1: What is the fuel remaining that 'just covers' the fuel pump (whether or not it's actually necessary to cool it).

Quote:
Originally Posted by cn90 View Post
This thread is getting to be pointless
I think it's a valid question, as yet unanswered for keeps.

Quote:
Originally Posted by cn90 View Post
Why would anyone in the right mind run the gas tank down to 2 gallons?
Lot's of reasons.

One is that they give you an 18.5 gallon tank so that you can use the gallons. It's not a 14-gallon tank. (It actually takes more than 18.5 gallons based on the aforementioned thread.)
- Are all E39s 18 gallons of fuel?

Another reason, for me anyway, is that the gas station I go to is off the beaten path (for me) so I have to make a special trip to the SJC airport. Why make a special trip when you still have 5 gallons of fuel? Postponing that fuel-only trip, I can make it days later when I am running an errand in that area (or feel like shopping with huge baskets).

Quote:
Originally Posted by cn90 View Post
getting stranded in winter = danger
In San Jose? The worst thing, weatherwise, that will happen in a San Jose winter is you'll get slightly wet from the wintery days-long drizzle.

BTW, I run mine to the double dash all the time and I've never been stranded sans fuel, on the side of the road.

There is a LOT of fuel left, even at the double dash point (I've never tested it to finality but I've put in over 18 gallons quite a few times).

Quote:
Originally Posted by cn90 View Post
In the summer = getting stranded and frying one's fuel pump.
That's the other key question which is perfectly valid:

Q: What would we expect a 'fried' fuel pump to look like (and where are the autopsy photos)?



Last edited by bluebee; 05-17-2011 at 12:14 PM.
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