Strange fuel gauge reading on 560SEL
 

The last fill up, I filled entirely and added a bottle of Techron Chevron to clean out the system after a long hibernation period. Today, as I'm nearing the reserve mark, I noticed the gauge now dips below the R but does not light up that its at reserve. Then it goes up a little and then it fluctuates from slightly above the R and then below the R... while the reserve light has not lit up. I'm planning a fill up today, but I'm worried that my sender could be dieing for some reason.

Car is a 1990 560SEL with 68xxx miles.

most likely just goo dude.. Chances are the techron and using your car is loosening it up and playing w/ your fuel sender in the mean time.

Jonathan

Jono... will this go away eventually with more techron or is this something where I'll need a new sender to correct?

usully it will go away w/ regular use...I wouldn't be to worried. In the mean time just fill all the way up when you go to the station and keep track of your odo..you can usually bank on an avg of around 17 to be Safe.

jonathan

Thanks for the info Jonathan:)

Its just an idiot light, you really don't need it.

But if it bothers you its probably a bad connection in the system, or a faulty sending unit. I am not familer with this system since I have not fixed this problem...yet...:D

Aren't "idiot lights" the lights that light up during start up? If so, I'm not talking about that... just the gauge fluctuating back and forth. Now I do know the 560 loves to gargle its premium stuff around the city, I don't think its to a point where when I look at the gauge it fluctuates back up and down;) :D

I filled half a talk last night.. will see how it plays out when I reach the reserve area.

I thought you were talking about the low fuel light or whatever MB calls it not coming on. If the guage bounces around that may be a bad ground as well.

The less PC name for dash lights are idiot lights.

goo likely
 

Just had the same occur in mine and it turns out likely to be goo buildup on the sender and throwing the readings off, Keep filling with known clean fuel from a major supplier and use the fuel cleaner it should go away after a few tanks.

Mine did after just two tanks and fuel treatment, now back to normal all the way down to the reserve.

If the 90 sender is like older ones there is a bobber (float that works like a fishing bobber) that slides up and down while contacting two thin wires. That tells the gauge were the level is. Near the bottom of travel the low fuel lite is activated by the float touching another contact. These contacts need use to stay clean. They get a film or coating or maybe its an oxide reaction with the gas, don't know. Maybe even a coating wears through on the lower areas of the wires and the lite contact. My wife never lets her gas get below 1/4. I've got a 67 250SL that isn't used much and when I get the level low it gets irratic response on the gauge. The sender is easily accessible on many benz's throught the trunk floor and a removeable access hole. The sender comes out simply. If you have some time you can take it out and measure the change as the bobber goes up and down. getting the bobber to slide up and down enough should clean the contacts and it should take a few months or years if you are lucky, to get coated again. It took 15 years to get this way.

Ive had success taking the senders apart and cleaning them in the past, on 3 of my diesels and most recently on the 500 and 560, be carefull while its apart, the wires are very thin and delicate! wipe them all down or use some type of cleaner if you prefer.