Just started to do this on me last week. Reads in the 85-90C range most of the time, but occasionally drops to zero every so often.

This is the gauge that measures water temp, just to the left of the oil pressure gauge on a 1982 300D.

I'd like to trace the connections back from the source, and if it is in the dash components, to forget about fixing it. But if it's loose along the way I suspect I can probably fix it.

Does anybody know where this sensor originates on the 'sending' end? Is it somewhere on the radiator block?

The temp sender (single wire) is in the middle of the block near the glow plugs. Try cleaning the connection there. Other places to check are the various grounds including connections inside the cluster.

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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

Sounds like the temp sensor itself may be ready to go. I had a similar issue on my VW TDI (I know, different animal) but just the same, a new sensor fixed the issue.

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2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)

Thanks for both replies.

Where is the sensor? Is it the same as the sender, described above?

It's the same thing. The sender/ sensor is pretty rugged and rarely goes bad. It's basically a resistor that changes value according to temperature.

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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

Check the body to engine ground strap. Make sure it has clean contacts on each end where it is bolted.

I had a jumpy Temp gauge, and this was the issue.

Charlie

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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

Yes!

__________________
2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)

Sometimes, people report success when they replace the sensor, but keep in mind all it might take is re-making better electrical contact at the sensor you've got. Putting a new part in works, sure, but rule out the simple and free stuff first.

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Cheers!
Scott McPhee

1987 300D

Thanks. Where is that? That actually sounds plausible, since it works intermittently.

The ground strap is connected to the front of the transmission bell housing, driver's side.

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1984 300D, 228k, Light Ivory, Java MB-Tex

Needle is back to rock solid.

Cleaned the contact at the engine block with WD-40.

Checked the ground strap...it was solid, but interestingly, I had a fuel injector return line leak out of #3 that was dripping down through the chassis and going right over one of the ground strap bolts.

Replaced that bit of return line, wiped everything down, and it all seems to be as good as new.

Thanks for all of the help.