T-Roll

After I bought my used 2001 E55 in early March I drove it home to San Diego and filled up with the gas the next day. It took 12.88 gallons and the guage read full. Only 20 miles later - of normal driving - the gas guage began to come off of full. Is this typical?

I drove it until the reserve fuel warning light came on plus another 20 miles or so. The tank is supposedly 21.1 U.S. gallons which includes a 2.6 U.S. gallon reserve. The thing is, when I went to fill up, it only took 16.79 gallons until it was full. The math doesn't work out on that, though. If I drove it into the reserve that is 2.6 gallons large, it should have taken approx 19 gallons to fill up.

Something seems fishy to me....what am I missing here?

Thanks.

Sathinas

I'm pretty sure it's 21.1 US Gallons.

Maybe the fuel level sender is going bad...?

As far as the fuel gauge sticking to 100% for a while after a fill-up, I'm willing to bet you may have overfilled the tank a bit.

MBFLO

just drove other day till it said zero miles then after couple miles it read 2-3 miles left . but i was on E when i filled it up it read 17.8 gallons

Schweinhund

That's about right. If mine is down to about 10 miles left in range, 1 gal or so, I can put in about 18 gals.

T-Roll

Sathinas - mine seems to come off of "full" too fast....not too slow. Seems like I barely get 20 miles down the road and my needle is already coming off of full.

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Regarding my tank size: if I run it down to where I only have 1-2 gallons left, then I should, by definition of a 21 gallon tank, be able to put 19-20 gallons in it when I fill up. But it is only taking 16 gallons or so before being topped off at the pump. Something seems wrong with this picture.

desired_speeds

Mine does the same thing, but on a lighter scale. I fill up full, the first 1/8 or 1/4 goes down quickly then it slows down. When the light comes on, I only fill up 16-17 gallons unless I drive it around a lot more, then I fill up 18 gallons. When I pumped last time, the needle never reached full, it only went to just over 3/4. The next morning when I started the car, it was full but then it dropped back to 3/4 not too long after driving. Maybe it was the pump this time.

AMG_Drvr

I've noticed the same issue with my '01. I guess I also notice the ground is never level at a gas station. It always seems to put the nose down or a slight incline or one side is down a bit. I'd imagine it would mess with the tank knowing whether it was actually "full" or not. I'll be honest, I'm not sure if there's a float in there or if it's gauged by pressure. I just gave up trying to figure it out and enjoy the miles and fill it up when it hits 3/4 of a tank.

Sathinas

No pressure is involved in fuel tank level readings... unless your E's run off compressed liquid hydrogen?

Then, maybe it's sticking in the upper range and once the fuel quantity in the tank drops to a certain level, the sending unit float gets "unstuck" and falls on top of the fuel...?

Also, remember, the fuel tank gauge is never going to be 100% correct, because the sending unit is not going to be 100% accurate.

Some gauges work in an "instant" fashion. For example, if you have 1/3 of a tank you you accelerate hard, the fuel gauge will move up or down due to fuel sloshing around, depending on how the sending unit is positioned inside the tank. GM loved this scheme in the past, don't know if they still employ it.

Other more sophisticated systems, work on an "average" scheme. The gauge will not instantly move up or down based on the fuel inside the tank sloshing around. They average the fuel sending unit's reported fuel level over the course of seconds. FORD uses this scheme. I don't know which scheme MB uses, since I turn off the car when I fuel up and I don't drive like a maniac.

I'm willing to bet the fuel sending unit is going bad. I know too many people who thought they still had a couple of gallons in their tanks, only to be left stranded on the side of the road with no fuel in the tank. This is not a Mercedes thing, all manufacturers suffer from this problem.

AMG_Drvr

@ Sathinas - you just brought back a great memory when you described the "instant" reading and the sloshing of the gas. My Mom had a '65 VW Beetle when I was growing up and she was a pretty aggressive driver. Whether she was going around a corner or slamming on the brakes the needle would go from one end to the other...lol. The hubcaps always came off that thing too. We'd hit the brakes and one or more would just keep right on going thru the intersection - and off I'd go running after them. Mom just had knee replacement surgery yesterday so she's in the hospital. THANKS for letting me go down memory lane - I'll have her cracking up tomorrow!

Sathinas

I hope she gets well soon.

Just don't call her "hop-along'.

DRBC43AMG

Some may remember the Beetle before it had a fuel meter.... You dipped a wooden stick with graduations marked on it in the tank to "read" what was still inside. You could also look inside as the cap was at least a 3" diameter. You also had a small gas reserve in the tank which you switched on by way of a small lever on the footwell next to the pedals when the engine would start to splutter when low on gas

croweld

I'm pretty sure the reserve is 3 gallons. So 16.79 + 3 = 19.79 and you probably were not at 0.0 gallons left on the in-dash indicator. So I would say it all adds up. I used to think the same thing when I first got my 2000 E55 but the reserve actually does count towards the 21.0 gallon tank. try driving it until the in-dash gauge says 0.0 gallons in the tank and then fill it up.

croweld

Even with the in-dash gauge saying 0.0, you still have 3 gallons of reserve so you should get ~18 gallons during a fill-up.