My fuel gauge has been acting up for about six months now, in strange ways. Initially I noticed that the needle would no longer quite get to 1/1 even with fuel visible in the filler neck. This wasn't really a problem, just meant that my reserve was around 3 gallons instead of 2. A few months ago, though, it started reading high—which is very much a problem.

Through both of these problem, the needle has never been jumpy, and the gauge readings have always been linear. Currently it reads almost exactly five gallons high, so that empty is right about 1/4 on the gauge, 1/2 is a quarter tank, and full is somewhere above 1/1 (I assume the needle pins at the 1/1 mark)

What gives? It doesn't seem like the sender could be at fault, since the problem changed from reading low to reading high, and the needle still moves a quarter of its travel for every five gallons like it's supposed to.

__________________
RIP:
2011 E350 BlueTEC, Schwartz 81k (totaled by uninsured drunk driver)
1964 Unimog 404.1 (wrongfully towed by the city)
1994 E320, Brilliantsilber 208k (transmission shuffled off after sudden catastrophic fluid loss)
1982 300D, Silberblau under a blue repaint 256k (sold for parts)
1995 E320 Polarweiss, 131k (sold for parts)
1995 E300D Polarweiss, 287k (totaled by drunk driver)

How do you know it's reading high? Did you run out of fuel when it was reading a quarter tank?

My car suddenly started running out at a quarter tank when the buildup of biologicals in the tank plugged the strainer.

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-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250

It's almost all electric so it's likely corrosion might have crept into the connections. Try cleaning all the contact points, at the connectors, at your electric center and at the instrument cluster. The only other thing it could be is the mechanical part of the sender in the fuel tank that doesn't let the float in the sender move freely.

Remove the sender and clean it. The float rides up and down through a tube, and much crud can build up in the bottom of the tube preventing it from reaching the bottom.

Okay, so now I'm well below 1/4 tank and still running fine. This makes me think crud in the sender, that perhaps gets periodically flushed by the motion of fuel in the tank and then builds up again. Looks like I'm going to have to track down that giant socket, what is it, 42mm on the sender nut?

__________________
RIP:
2011 E350 BlueTEC, Schwartz 81k (totaled by uninsured drunk driver)
1964 Unimog 404.1 (wrongfully towed by the city)
1994 E320, Brilliantsilber 208k (transmission shuffled off after sudden catastrophic fluid loss)
1982 300D, Silberblau under a blue repaint 256k (sold for parts)
1995 E320 Polarweiss, 131k (sold for parts)
1995 E300D Polarweiss, 287k (totaled by drunk driver)

The design of the sending unit in the tank will not allow this.

__________________
Jim