Ok, I've seen this topic discussed before, but I have noticed something I think goes beyond coincidence.

I've owned three MBs. A 1971 250, a 1977 280E and now my 1989 300E. All three cars have (had) relatively high mileage. On all three cars, the fuel gauge has the same problem. It is accurate at the full level, but as the fuel level drops below 1/2, the gauge is useless. It ping-pongs from empty to 1/2 full. The weird thing is that on all three cars, the RESERVE LIGHT is dead accurate. In fact, that is how I determine how much fuel I have left. I fill the car up, set the tripmeter and then watch my mileage and watch for the reserve light. Sometimes when the reserve light comes on, the gauge actually reads on empty, but other times it reads as half-full or somewhere in-between. It seems to be random in that sense. The reserve light, however, is accurate to within 10-15 KM (I get 525-575 KM on a tank depending on driving conditions).

Now, I have read the other threads here and I have since removed the sender unit and inspected it thoroughly on all my cars. The wires are clean and the float moves freely up and down the wires. I cleaned the wires anyway to be sure. With the unit removed, I have flipped it up and down and watched the fuel gauge. It appears to work just fine, but then again I am shaking it rather erratically compared to the relative motion it must experience within the tank, so it is hard to guess.

All the other gauges on the cluster are fine (temperature, oil pressure, economy gauge). Only the fuel gauge is off. As I said, it reads from full to 1/2 fine, then loses its accuracy completely from 1/2 to empty.

The weird thing is that I have this same problem on all three cars, all with high mileage and all from different years. My mechanic is as perplexed as I am. I am wondering if there is some fault with the gauges themselves. As some people have mentioned, the gauge is not linear. It appears to move from full to 1/2 more quickly than 1/2 to empty, which makes sense. Perhaps the lower half is at fault?

Anyone have any opinions?

zues,
i have the EXACT same problem with my '77 240D. the meter reads well intil it hits about 1/2 full, then i notice that it will sit on 1/2 for a few days, then it will dip, dive, shake, and shoot back and forth from 1/2 to R (never all the way to empty). the only difference is that my reserve light never comes on. maybe my bulb is out, or maybe my gauge is in even worse repair than yours. do the needle and the reserve bulb work with different sending units/sensors? i was thinking about taking out the sending unit for inspection....... can anyone offer any sound advice on the issue?
thanks,

I have the same problem, and have been told by my tech that if the grounds and wire connections on the back of the guage are all perfectly clean and tight and making good connection, and the sending unit is good, then it is the guage unit in the dash that is failing. He said that given the costs of guages, unless I just couldn't stand it, to live with the problem, especially as the reserve light and top half of the guage are still accurate. I have taken his advice, and use the trip odometer for a confirming device - when it gets over 250 miles on it, I fill the tank regardless of what the guage says. Sort of a Digital gas guage!

[Edited by JCE on 02-17-2001 at 02:22 AM]

I have the exact same problem on my 73 280. I replaced the sending unit about $100.00. It worked fine for about three months and then went right back to the way it was.

I've been told that the reserve light works with a switch, not the sending unit. That's why my guage can read 1/4 tank and the reserve light will still come on, meaning that I only have about a gallon left. My reserve light does always come on with the ignition on, prior to starting the car. This is how you can verify that the bulb is not burned out.

I test the GAUGE by subsituting a varible resistor for the sending unit. You need a 0-100 ohm pot to duplicate what the sensor does. That way you can tell whether the sending unit or gauge is bad.

The contact for the light is indeed seperate from the fuel level resistor.

By the way, my 85 380SE is doing it too. On a funny side note, I have a subwoofer in my car and when on the verge of the light coming on, the light will pulse with the beat.

Q: Do you notice any other lights flickering with the sub beat? You may be looking at current/voltage drop from the sub draw - might consider a large capacitor for the sub, and possibly upgrade to the alternator/battery during the next change. If the current/voltage are pulsating for your lights, all the rest of your electronics in the car (Sensors, computers, etc.) are experiencing the same thing, which often shows up in electronics as accelerated wear.
I am going to install the new stereo and sub next month, we'll see what happens.

The gauge on the 280SEL sometimes does the wiggle thing, and I too simply used the trip meter for an accurate guage of when to fill. Now however, the odometer/tripmeter has decided to stop working all together, so I am now guestimating everything from miles driven to MPG to "I wonder if it's time for gas" :eek: .

This weekends project is - pull the cluster and get the speedo head ready to ship off for repair.

Both of my Mercedes,Show empty,when there are a lot of gallons of fuel left.That is if the stated capacity is correct.I am tempted to run the gas one out someday to find out how much it really holds.Michael

many times i have just run the car untill it sputters and stalls at stop lights:):) not good practice i know, but since my odo works irratically, i cant trust it either. ive found that after i run it this low, it'll hold about 28gal!!! i didnt know these cars had such big tanks. i get 600-700 miles out of an ENTIRE tank. (a rough estimate on account of the odo)

Eureka!
 

So THAT's what the gauge on the top left is for! I too thought the trip odometer was standard equipment on MBs to ensure the driver can figure out how far they can go before the tank is dry.

I have Dennis Adler's "Early Speed and Opulent Luxury: The great Cars", and on page 30 they show a beautifully restored 1915 Oakland Model 37 Speedstar with a gauge on the gas tank in the back. It was a new convenience, designed to improve on the old "walk around the back and dip a stick in it" method to check the level. How many current MB owners would use the stick method today if the tank fill line didn't bend?

My 1980 300D (235k miles) has an erratic gauge and no reserve light function. My 1991 300TE 4matic has the above mentioned inaccuracies < 1/2 tank and a working reserve light. The reserve light is a very helpful tool. I don't know what I'll do if the trip odometer dies!

Designed for wealthy owners...
 

Seems it must be a characteristic fault built into most Benzes! My '87 190E does this also. Maybe MB didn't expect their aimed market wealthy customers to only run on a half empty tank, little expecting there'd be us skinflints trying to run them years down the line on fresh air wherever possible? :-)
James UK

Wow!

I somehow knew I wasn't alone with this problem. It seems that MB fuel gauges are crap. Funny. We have an ancient Ford ('65) truck up on my stepfather's farm which still has a perfectly accurate fuel gauge - he uses it to gauge his mileage. Now why can't MB come up with something a little more reliable? I for one am sick of explaining to anyone who borrows my car my little system of fuel monitoring...

"OK, now watch the tripmeter. When it hits 500KM, watch for that little reserve light. When the reserve light comes on, you've got about 35 KM to find some gas. Oh, and ignore the needle, it will be doing a nice little dance for you..."

This explanation is almost always followed by a sarcastic remark by my friend(s) about Mercedes quality, etc. and how their little Toyota or Mazda has a perfectly working fuel gauge.

I'm going to write to MB and ask them about this problem. Don't know what good it will do, but it is annoying that they have never addressed the issue (unless they have and I don't know about it). Do they not consider fuel a big issue? I mean, the stupid and useless "economy" gauge works just fine!

Or perhaps, as James said, we are all supposed to drive above 1/2 all the time with our only worry being where to store our big, fat, bulging wallets. ;)

JCE,

Nope, the voltage is fine. When the fuel level is just right, the bass will cause the float to move just enough to make the light come on and off to the beat.