This is for a 1987 300SDL - this car is new to me... I filled it up and started driving on a long journey home. When the fuel level got down to about 1/4 I started watching it and looking for a station. It was then that I noticed that the fuel gauge behaved strangely: it kept jumping from 1/4 full all the way down to completely empty, then back up again. There was no pattern to it - not that I could pick up... it was doing it even when standing still and not moving! When I filled it backup it was back to normal producing smooth indicaiton of where the fuel was....

Is it the fuel sender unit, perhaps or something else to check?! Are there any serviceable parts in the fuel sender unit?

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1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K

My 240D does that. I'll be watching this thread, even though I anticipate retiring the car early next year. (To be the tranny donor for my 300's 4 spd swap.)

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

It is the fuel sender - most likely, there is a patch on the fuel sender contact strip that has gunk on it (fungus) which makes for a bad connection. The sending unit is serviceable, there is a DIY or two on removing the sending unit. You might want to try running some soltron or biobor through the tank first to see if that solves the issue...did for me.

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth

My 240d sender was still jumpy even after I took it apart and cleaned it. I literally had the float in my hand and watched the guage, below halfway the needle would just jump back and forth spasticly. I ended up snagging a "good" one from the jy (it had rust, but with the rust removed it worked better than the old one).

Should add - when/if you take the sending unit out, make sure you don't break the fine ground wire, that will trip the reserve light if it becomes disconnected.

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth

Check gauge grounds; check tank strap grounds.

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Regards,
Ian White

1995 E300 Diesel w124 OM606
2014 E550 w212 M278 biturbo

2001 BMW 740i E38 M62 (past)
1981 300SD w126 OM617 (past)

*2

My 300D had a bad ground and running a new wire to the collection of the grounds behind the wheel definitely helped.

I also cleaned out the sender, but it was oddly very clean.

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-Typos courtesy of my mobile phone.