My fuel gauge indicator just started to have what seems to be an intermittent electrical issue. Swinging hard from the fuel tank reading to below zero as the reserve light flashes on and off with it.

I can imagine it would be either the sending unit failing or a loose connection on the sending unit power supply circuit.

From the looks of the cost of a sending usnit I am hoping for a loose wire. Any thoughts on where to look first would be appreciated. Thanks,

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2012 B Class

1981 300D - Now with greazzer

Its not a big deal to pull the sender. You go at it through the first aid kit recess. There is a little nut on the bottom that allows you to remove the bottom plate on the unit & then the plastic piece. The long outer tube then comes of & exposes the workings. Be careful not to damage the 2 thin wires that run the length of it. Hopefully a good clean out will fix it.
Good Luck !!!!

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Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

Its poor grounding of the cluster, not the fuel gauge. Run a ground wire from one of the cluster's screws to the chassis.

I think you may have a good point, because when it cycles intermittently to zero, it always returns to the current level, not the other side.

Loose ground or return wire makes sense. Thanks.

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2012 B Class

1981 300D - Now with greazzer

My needle jumped, but the low light didn't come on. The jumpy needle was caused by crud on the sender wires. It only happened below half a tank. I had to clean it twice, the second time I used acetone and was much more thorough. The crud would break the connection and the fuel level sender circuit would become 'open'.

The jumping needle + the lights simultaneously sounds more like a wiring problem since they're separate functions on the sender.

I think there are good pics of a gunked up sender in a thread from Army.

My fuel gauge works most of the time, my odometer gave up at 276,000 miles - years ago. I rely on Garmin to tell me when I have crossed 300 miles. This post has made me wonder why my low fuel level light no longer illuminates? All the rest of my instrument panel is well illuminated...Any ideas? Go Bears>>>

If you're only going 300 miles on a tank then you probably aren't even getting it nearly low enough to trigger the light.

Does it come on with the switch on, engine off, during the usual self test while you glow?

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~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

The fuel indicator light must also be from a point on the fuel sending unit. Now my light has gone on solid. Will dig onto it this week.

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2012 B Class

1981 300D - Now with greazzer

My light only comes on then the tank is full! Not very handy, a light to tell you when the tank is full. The gauge is jumpy too, figure I just need to clean the sender and see what happens.

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1981 300D - {172,000}
1971 220D {Sold to TomJ}

The light comes on when the float makes electrical contact with the bottom. The gauge is based on the "loop" of wire (float sinks, loop gets bigger, more resistance, lower reading on gauge...) so the light isn't really linked to the needle position or a "point" in the sending unit except the bottom.

You can also get a light from an alternator and/or bad cluster with no effect on the gauge, but those normally come on together. I'd clean the sender and see what happens. Maybe your float is gunked to the bottom?

See the pics for what it CAN look like.

http://www.peachparts.com/shopforum/showthread.php?t=277167&highlight=sender&page=2

bustedbenz,

My low level light does not illuminate when I start the car. The only lamps that display are the battery, brake wear, glow plug, etc.

Before I tear the fuel sender out, any other ideas?

Replace the bulb first.

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----Adam

1985 300SD 322,000

bustedbenz,

Your comment re milage intrigue's me. As neither of my odometers work (trip or accumulator), and my fuel gauge is not reliable, I rely upon a garmin to monitor the miles between fuel fillups. Typically I target 300 miles as refill time. Typically I put 17 - 18 gallons in before the foaming diesel spews from the filler pipe. I believe that the tank in a '82 300 sd allows just over 20 gallons.

So my questions are:
apparently my milage is below par, what should I expect?
at what point should I expect the low level lamp to illuminate?

I have had this vehicle for almost two years, and have come to truly appreciate the vehicle.

Bill

If I pull the instrument panel to replace the low level lamp, I may as well pull the odometer at the same time. Do you know if I can operate the vehicle with the odometer removed, or do i need to park the car while the odometer is repaired off site?

That's correct. Unplug the connector from the sender, the light should go out which indicates a short inside the sender. Here's a thread with pinout info of the sender and switch.

http://www.peachparts.com/shopforum/showthread.php?t=195390

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked