Gas tank size

[vdubpower]

is it true that out tanks are only 17 gallons where as the rest of mercs line is 21.Or atleast the E class is. It seems that the fuel low notification goes on right when i go under a quarter, but does that mean i only have 2 gals left, just doesnt seem right?

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[otakki]

I also noticed the gas tank size difference last week: 17.4 vs 21.1. I bet they did that due to the increased efficiency of the M157 and other E class models. The tank size in MY2010-2011 E63 is 21.1. The low fuel notification also comes up at the quarter mark for my '10 car. However, I figure each mark is around 5 gallons so I figure that's how much is left at that time.

[hyperion667]

thought it was 18 gallons

[otakki]

In the summer and warm climate, it's a good idea to have the fuel tank at least around half full since most fuel pumps sits in the tank and rely on the fuel to cool itself. However, my old car usually gets filled when it's nearly completely empty and the fuel pump seems to be working well since the day I bought it new around 19 years ago (keeping my fingers crossed).

[vdubpower]

increased efficiency, come on now, these cars are still only 16-17mpg

[Snipe656]

Originally Posted by otakki

In the summer and warm climate, it's a good idea to have the fuel tank at least around half full since most fuel pumps sits in the tank and rely on the fuel to cool itself. However, my old car usually gets filled when it's nearly completely empty and the fuel pump seems to be working well since the day I bought it new around 19 years ago (keeping my fingers crossed).

I do not know if this logic holds true any more but I do know around 20 years ago it did for those fuel systems. Suppesedly having closer to a full tank also helps out in fuel economy due to the added volume in the system. I forget the actual stated reason behind it and I am sure the gain from driving around always near empty v. always over half a tank is pretty minimal.

increased efficiency, come on now, these cars are still only 16-17mpg

But in the grand scheme of things that is pretty good considering the weight of the car and not even taking into account the available power. I bet your 1985 SEL in your signature does not do better and maybe even does worse? I seem to recall my old 500SEL and heck even the old 380SE all guzzling their fuel.

Last week I was reading a news article about AMG and their efforts for increased fuel economy. Actually is some pretty impressive measures they have been taking. Can't help but wonder though if they will effect long term reliability though.

[otakki]

It will be interesting to find out how a full tank will help with fuel economy since it's actually additional weight for the car.

[Snipe656]

Originally Posted by otakki

It will be interesting to find out how a full tank will help with fuel economy since it's actually additional weight for the car.

I tried searching earlier but could not find it. When I read it, it was a physical paper/study on things. It made sense at the time but I do think it was very specific to the fuel system style being used in the cars for that study. As I remember(going on old memories here) it was a return style fuel injection system and the root reason they gave was something to do with available volume for the fuel pressures/consumptions needed.

When I searched earlier all I found was speculations about evaporation factors, fuel pump temps and so on. None of it seemed all that conclusive one way or the other.

[503C43 ////AMG]

Originally Posted by Snipe656

I do not know if this logic holds true any more but I do know around 20 years ago it did for those fuel systems. Suppesedly having closer to a full tank also helps out in fuel economy due to the added volume in the system. I forget the actual stated reason behind it and I am sure the gain from driving around always near empty v. always over half a tank is pretty minimal.

This would explain why I get 140-160 miles on the first 1/2 of the tank and only 80-120 miles on the second half of the tank. I always thought it was just an inaccurate fuel level sending unit (which it very well may still be).

[Snipe656]

Originally Posted by 503C43 ////AMG

This would explain why I get 140-160 miles on the first 1/2 of the tank and only 80-120 miles on the second half of the tank. I always thought it was just an inaccurate fuel level sending unit (which it very well may still be).

From what I remember it would not been that significant of a savings. I bet what you are seeing is how the gauge does not tank into account fuel within the fill neck. I doubt any car manufacturer out there calibrated their sending units for the fill necks and tanks.

[looney100]

I call bull!@#$ on a couple of the comments here.

1) Yes, fuel is used to keep fuel pumps cool, but the fuel pumps are located at the bottom of the tank. You don't need to worry about overheating unless you're running for extended distances with an empty tank - not an easy thing to do.

2) The only affect the fuel level will have on economy is the tiny effect the additional weight will have on rolling resistance, meaning that a full tank would result in a tiny decrease in economy. The computer injects fuel based on a number of inputs - none of which is the level of fuel in the tank.

[Snipe656]

Like I said what i read was around 20 years ago and was very specific to a certain car/fuel system type. The whole premise of it was actually how many people would run their cars near empty for less weight and therefore faster times when racing(straight line racing) but how the less fuel in the system resulted in less volume and did result in more fuel consumption for daily driving needs. Basically what it was getting at is people would be driving around the city with near empty tanks for hopes of being faster for when the urge came up to do so. It was extremely detailed study and certainly could been still pulled out of someones rump. It was a return style fuel system and used an intake fuel pump but one mounted in the top of the tank so had a sock pickup on that towards the bottom of the tank.

I would highly doubt these cars even use the same type of fuel system let alone have many other different variables such as direct injection and so on.

I have no clue about hot fuel pumps and fuel but interesting to see Mercedes apparently went away from external fuel pumps. Last fuel injected Mercedes I was under had the Bosch fuel pump and filter outside the fuel tank.

[vdubpower]

the 500 gets me a nice 13-15MPG and the denali is stuck at 13,

its nice to have a bunch of v8s

[otakki]

Originally Posted by vdubpower

increased efficiency, come on now, these cars are still only 16-17mpg

That fits your slogan of "driving them all fast and hard." Strangely, it seems I get better mileage when crusing at around 80mph than at 55mph for my M156 (6.2). I don't know if it is because of the ultra low Cd of the W212-0.26 for regular W212 but not sure about the E63. Anyway, I get around 21.5 to 22mpg with it set at S+ for needed spirited driving. Hmm, maybe the driving needs to be more spirited.

I woud like to have an instantaneous mpg indicator just for a few hours to find out what's the optimal cruising speed. I think the regular W212 has one of those.