donnieR32

So, just picked up a 2009 ML320 BlueTec and love it. It came down to it or the diesel Touareg and I couldn't pass up the deal on the BT and I love it. This is my second Benz (2007 CLS550) and they both have 1 feature that I absolutely hate. Once you get to about 50 miles remaining on a tank of fuel......boom, there's an image of your vehicle being fueled. How about continuing to inform me whether I have 50 miles or 5 miles until I'm out of fuel.

I usually won't push it, but if get home and it says 100 miles to go I should with confidence be able to make it to work the next morning if it's only a 40 mile drive. Of course, by looking at the gauge you'd think I was on fumes and I can no longer see how many miles I have left. Last I saw was a range of 40 and I'll be stopping after work to fuel up. Luckily, the station is only about 2 miles away. Sorry, to use opening post as a rant. Either way, love this truck.

N_Jay

Yep, noticed that on both my GL and E.


Seems that when the low fuel light comes on you get the symbol, that you can cancel and get back to miles. Then when 1/2 that fuel is gone you get a symbol you can not cancel.
With the gas engine that is at about 20 to 25 miles and is probably a good idea, but with the diesel it is 40 to 50 miles and annoying.
Sometime later the symbol turns red, but I have only driven that far with the E (Gas) once. I think it was at about 10 to 15 miles left, but I am guessing.
I assume the GL (diesel) would do the same.

donnieR32

That is good information. Not that I'd push it that far, but once that symbol comes on and you still have 40+ miles left it causes unneeded anxiety.

N_Jay

I'm guessing it is trying to judge the gallons left, and with hills, corners and fuel sloshing, it makes the safest measurement possible.


I read somewhere that MBs have a 6 liter reserve, so maybe the first warning is at 12 liters, and the second is at 6. (and RED at 3?)


I have also seen reference to a 9 littler reserve. Maybe this is for diesels or larger tanks?

amdeutsch

The legal system in the US comes to play here. For everyone that will treat this as just a guestimate instead of an actual there is less of a problem. But we all know there are those that will say; if MB says so it must be because I spent all that $$$$.

There are numerous other examples of such displays. Some cars and their TPMS will only provide a warning and not a readout. Etc. Etc.

donnieR32

Honestly, I always wondered if there was a calculated margin of error for all those people that run it so low or out.

donnieR32

Filled it after work and put in 25.0?? gallons.

u001elg

Wow, put 25 gal in a 25 gal tank... maybe it wasn't crying wolf.

The Mile left is a calculated value, while the low light/message is off a float in the fuel tank. Sufficient margin is given that if you are on an interstate where than can be 25 miles or more between interchanges you would still be able to make it to the next station. If viewed in that manner, 40 miles left is not so far.

It has always vexed me as to why perfectively rational people will draw down a fuel tank so low. Once in a great while maybe, but on a routine basis ... never.

Forget about being stranded after you have run out of fuel (with a gauge and warning light telling you this)... but just the extra wear on the fuel pump, which is cooled and lubricated by the fuel flowing through it, and the fact that you are sucking up any dirt or crud from the bottom of the tank is enough for me to keep the tank above 1/4.

N_Jay

You are always "sucking up dirt or crud" from the bottom of the tank, the place the fuel is pulled from does not change as the tank gets emptier. (Todays fuel is very clean, so hardly a worry.


The pump is in fact cooled and lubricated by the flue, but unless you drive a long time with it stuttering and stalling, you are not running the pump dry. So again;no worry.


As for getting stranded, that is between you and the wife (and yes, you should worry!)


I have been shooting for "the next rest stop" only to find it out of fuel (or power) and then had to cross my finger to find another station, and have been driving fine on reserve and come up on a traffic jam adding an hour to the previous 25 min between rest stops.


Both unnerving, and have been reminded of both MANY times since. (Thank you dear, I forgot you reminded me 2 minutes ago)

u001elg

Hey N Jay, I will agree to disagree with you on your first two points...

The point that fuel is removed stays the same, but as the fuel level lowers, junk that
is lighter and is suspended in the fuel will, in effect, become more concentrated as the level lowers. Fuel is much cleaner that decades ago, but every time a truck delivers fuel and opens the cover to a below ground storage tank there is the potential to get some dirt/water/honey badger into storage.

The second was not just the fact of sucking air, which really can damage a georotor pump, but that a cooling mechanism of being submerged in relatively cool fuel is no loner available. Does this affect short term operation... no, but over many years and miles it does come into play.

I realize that one may consider this coincidental, but I had a father-in-law who habitually put $10.00 of fuel in his vehicle at a time and only when the gas gauge wouldn't move. Over a period of 5 years and 25K miles I replaced 6 seized fuel pumps for him. My personal vehicle I kept for 15 years and accured 409K; all on the original fuel pump.

N_Jay

I could agree with you, . . . . . .
. . . . . . . But then we would both be wrong.

Really? And in a moving vehicle that keeps getting filled form the top and drained from near the bottom while being stirred by the motion of the car, still lets all the dirty fuel just float (and by magic, none of the dirt sinks.


Sorry, FAIL! (#1)


Yep, but not enough to worry about. (The stations also have filters and water traps.)


So just how much time does it spend out of the fuel (considering it is getting splashed until very close to the end (probably almost to the end, and most pumps pull the fuel through so the internals are always being bathed even when the outside is not longer submerged.


Fail (#2)




I'm guessing it had something to do with it. Of course, that would be a couple of lifetimes more dry runs than what we are talking about.

u001elg

I could agree with you, . . . . . .
. . . . . . . But then we would both be wrong.



Yes Really... This has little to do with fill from the top and drain from the bottom. The tank has baffles to minimize sloshing and the pick-up resides in a well where the fuel return dumps the excess fuel from the fuel regulator.

It is simply differing density - an extreme example is to put packing peanuts in water and you won't get them to sink and stay at the bottom regardless of agitation... another example with two fluids is oil and vinegar - you can agitate them to a point but they will always separate.

As to fail #2 the answer is that the fuel pump starts to become uncovered at about 1`/2 tank and is fully uncovered by 1/4 tank. The next time you change the in tank fuel filter on your W211 take a look at the relationship of the pump position to the height of the tank. I agree that all in tank fuel pumps cool their internals with fuel flow, but that was not the point I was making... The additional cooling by being submerged in a body of fluid cannot but help remove heat and this adds life.

The original post by donnieR32 stated that if it shows 100 miles to empty a 40 mile trip shouldn't be a problem ... that definitely leads one to believe that this is a regular practice and could add to those couple of lifetimes of dry runs.

N_Jay

So all the dirt is lighter than fuel?


Well OK, then!

u001elg

Interesting...

No, not ALL contaminants are lighter than fuel, but a component of contaminants are lighter and will stay suspended or float until level is lowered and they are concentrated.

This is not an all or nothing situation: i.e. ALL dirt is heavier or ALL dirt floats

N_Jay

What is the process that causes the sorting by which the contaminants are "concentrated" in the upper strata of the fuel.


AND even if this was the case, by running the fuel down every tank (against some recommendations) you would never have more than one tanks worth of contamination in that last gallon.


Whereas, if you follow some who say to never run it down, the second tank would be twice as contaminated, and by 10 or 20 tanks, the concentration of contaminants would be far greater in even the bottom 1/2 than the bottom gallon in that first tank (and every tank if always run down).


By no set of logical thoughts can you get to the conclusion that running the tank to the normal empty level (not till it is sucking air) is worse from the system than not doing so.

u001elg

I see the concern, you do not believe that different substances have different densities or one substance can float on top of another or as a suspension.

Next time, in the grocery store, look at a bottle of Italian salad dressing and notice that the vinegar and heavier solids are on the bottom and the oil component and lighter solids are on the top with some solids suspended in the oil.

Even if you vigorously shake the bottle, the liquids and solids will separate themselves over time. Gentler sloshing of the bottle will blur the demarcation of the separation, but they will still remain separate. This, indeed is the process that causes sorting.

A relatively easy experiment that I have done with my design students in the past has been to take a one gallon flat bottom translucent plastic container (milk jug, spring water or equal does well) and fill with water (spec gravity 1.000) Add several ounces of mineral oil(spec gravity less than 1.0) and you will notice it floats on top. Now add any fluid with a specific gravity or greater than 1.00 (DOT 4 brake fluid usually works well) and you will notice that it falls to the bottom. If you like you, an add some solids, sand or equal. Place the gallon jug off center on a magnetic mixer and mix on medium speed. You will notice droplets of both fluids enter the water. To mimic a fuel system; use a small pump (aquarium pump or equal) and place the suction tubing about 3/4" above the interface between the lower fluid and the water. Slowly pump down the gallon container into clear 1 bottles ( 20oz soda bottles work well).

What you will notice is that the as the water is removed the first bottles are clear water with very little of the contaminants. As the water level is lowered, the heaviest fluid remains on the bottom and the lighter fluid lowers with the water level in between. The contaminants "sort" and "concentrate" as the water is removed such that at lower "tank" levels you will start to notice droplets of the mineral oil and eventually a brake fluid, water mineral oil mixture is being drawn from the tank and deposited into the clear container. Stop the pump when there is about a 3/4 inch band of water left.

This is the set of logical thoughts that get you to the conclusion that running a tank to normal empty (i.e. low level light on or yellow message) is worse.

You are also absolutely correct that a fuel tank has no method to remove contaminants except through the fuel filter and they will build up over a long period of time - many hundreds of tanks, not 10 or 20 since, as you previously stated fuel is cleaner today. This is one reason why methanol of ethanol "dry gas" is used to combine with water and allow it to be burned in the engine... or why a fuel filter has to be periodically changed from removing particulate from fuel. This is also why todays 10% ethanol treated gasoline does not build up water in the manner that pure gasoline does.

Now as to only having one tanks contamination in that last galloon: complete the gallon jug experiment several more times, filling with water and then add one additional ounce of each "contaminate" fluid each time. You will notice that more that the previous contamination exists between each interval.

Hope this helps clarify the discussion and provides a logical bases for the conclusion.

N_Jay

No.
I do not believe it is a significant factor in what we are discussing.

Interesting (but irrelevant)

Yes, except the amount of fluid with significantly differing specific gravity is insignificant, and the level of particulate contaminants is much less. Additionally the size of the particles is much smaller, and if they are absorbent at all they have absorbed liquids of the same specific gravity as the base fluid.
(In other words,. enough differences to render your analogy meaningless)

Interesting Macro experiment.


However assuming less segmentation of specific gravity, the segmentstaion is less; and a much lower level of contaminants, allowing them to be extracted without concern; it seems preferable to removes then in small doses over the life of the vehicle instead of allowing them to collect in the tank.


It clarifies the misassumptions your conclusion is based upon.

u001elg

The salad dressing analogy and Macro experiment are to illustrate the concept.

Some contaminants will collect in the fuel tank over the life of the vehicle regardless of you fuel filling philosophy.

Since you do not believe the basic premise of my discussion to be a significant factor, then you are correct... it most certainly clarifies your misassumptions that your conclusion is based upon.

Cheers

donnieR32

I don't routinely run it or any of my vehicles low. I'm the first person to call someone a dumb *** for running out of fuel in a car less than 20 years old. I just thought it was interesting that with 100 miles to go; a 40 mile trip can MENTALLY can freak you out because it says you're so low on fuel. I rarely go that low. Side note, today's trip to work I saw 29.0 mpg for the entire trip.

N_Jay

Around town, I fill the cars when convenient usually somewhere in the lower 1/4 of the tank, probably with the first low fuel warning about 1/4 of the time.


Winter time, usually 1st convenient time when below 1/2, but probably 1/2 the tanks go down to 1/4 or less.


On trips, rarely fill before the first low fuel warning, and probably 1/4 of the time hit the second warning.
Except when towing, start looking at about 1/4 left and fill below the first warning about 1/2 the time. Never have got to the second warning when towing.


I have never run out of fuel in 38 years of driving with a car with a working fuel gauge, and have not run out at all in over 31 years.


I have had about 5 fuel pumps replaced. All but one in one car with a known design defect and one in a RangeRover at over 130K miles.


Relax and enjoy the ride.

donnieR32

Only scare I had was with my '67 Shelby, but the gauge doesn't work and I had the motor rebuilt. It gets about 8mpg, and the gas station was the first stop after leaving my house...i coasted into the parking lot.

jkaetz

The range remaining is based of how much fuel it thinks is in the tank and how many MPG the system things you're doing at the time. It will fluctuate greatly if you're on the highway and then exit onto surface roads. It is unfortunate that it will not show an estimated range below 50 and I have my doubts about a red low fuel warning. My wife put 25.4 gallons in her 2011 Bluetec. I told her that's interesting since she only has a 25 gallon tank. She had been ignoring the light for a couple days and I doubt she would have ignored it had it turned red. I've taught her that red lights require immediate attention. Others can usually wait. Hopefully she won't do that again. *sigh*

On the fuel pump debate, aren't most fuel pumps dropped into a smaller fuel can, which is always full of fuel and thus submerging the pump, rather than simply sucking it from the tank as a whole? That would negate the entire cooling theory. On the dirt theory, I doubt the fuel pump cares about the dirt particles and the fuel filter is supposed to take care of any contaminants in the fuel. I've heard both theories used to justify keeping your tank full over the last 15 years most in reference to something their dad, or other relative, ran into back in the 1980's. To that I retort, we've now had over 30 years to improve things. No one now worries that oil change intervals are 7,000 - 15,000 miles versus the 3,000 mile limit in the olden days. Why do we still hold onto fuel pump standards of olden days?

2008 ML 320 CDI

I'm one of those who loves to keep an eye on the fuel efficiency of my vehicle and to know exactly what the fuel gauge is telling me so that I can have a reliable measure of how much fuel is left in the tank and how much further the vehicle will go without the risk of running out of fuel completely. I fill the vehicle up to the brim every time I put in fuel and this information is particularly useful on long trips from Alberta to southern California.


My vehicle is a 2008 ML 320 CDI and I thoroughly enjoy this vehicle. My wife says that I'm obsessive with the data and statistics that I keep, but I suspect that there are many others like me out there!


With that background you will understand that I just had to find out exactly how much fuel my vehicle holds and how much further I could go when the 1st and 2nd low fuel warning signals come on. The vehicle was filled to the absolute brim, was then run completely dry and filled up to the absolute brim again. Below is what I found:


* The tank holds 109,65 litres of fuel.
* The vehicle did a total of 1241 km on 109,65 litres of winter diesel at ambient temperatures of below -10 degrees Celsius. (Alberta, Canada)
* The average fuel consumption on this particular tank was 11,3 km/litre.
* As the vehicle was able to go 147 km from the point of the 1st low fuel warning signal coming on, 45 km from the 2nd warning signal and using the average fuel consumption figure of 11,3 km/l, calculations show the vehicle has 13 litres remaining when the 1st warning signal lights up and 4 litres when the 2nd warning signal lights up.
* When the vehicle was run dry, the vehicle started up within the first 6 seconds of cranking the engine. The diesel fuel system bled itself of any air locks (no manual bleeding was required) and the engine ran smoothly almost immediately after starting up. After this start-up the engine check light came on and it remained on for 3 or 4 full run cycles before the onboard management system turned it off again.


Now that I've done this I am unlikely to have the vehicle run out of fuel completely. Under normal conditions I fill the vehicle up whenever it gets close to the 1st low fuel warning signal.


What puzzles me is that this and much more information that I would like to obtain, must be available from the vehicle manufacturer but there is no way of obtaining it directly from them. Granted most people are not much interested in this kind of detail but for those of us who are, there ought to be an easier way of getting it.

N_Jay

So you have confirmed that the ML (and probably the GL) does not have the third (Red) fuel warning?


Interesting.


I guess I won't wait for it to come on.

2008 ML 320 CDI

Yes, I did not see a 3rd warning signal.


The first warning signal (picture of a filling station pump if I remember correctly) came on at the same time the small orange light at the bottom end of the fuel gauge lit up and the fuel gauge needle was on or close to the 1/8 tank point. At this point all the other menu screens operated as per usual and the vehicle ran dry 147 km later.


The second warning signal image showed the ML front elevation next to a filling station pump and with the fuel hose connected to the vehicle. At this point information for the remaining range is turned to a blank. Just before this signal came on, the last number I remember being given for remaining range was 52 km. The vehicle actually ran dry at 45 km from the point of the 2nd warning coming on and the vehicle ran dry near the top end of a 4 km long hill. If the vehicle had been travelling on a level stretch of road instead at this point, perhaps it would have been able to draw on a little more fuel in the tank in which case the total tank capacity could be a little more than the 109,65 litres.


Also, at this point (2nd warning coming on) I was pretty much concentrating on where I was going to pull over as I knew the vehicle was going to run out of diesel soon but I didn't know exactly where! I didn't mention this before but the vehicle was being used on my daily commute at the time and I had a jerry can with exactly 20 litres in the boot. When the vehicle did run out of fuel, there was very little warning in the way of power loss or stuttering (there was a slight hesitation and power loss for say 100 metres and then it cut out pretty suddenly), I managed to pull over safely and well off the road, put in the 20 litres of diesel and went straight to the filling station to fill up to the brim. In my calculations afterwards, I did compensate for the small amount of fuel used over the distance from where the 20 litres were put in to the filling station. So all in all the 109,65 l number for capacity could be off slightly, but this error should be less than 0,2 litre.