Hello everyone my temp. gauge is acting strangely on my 85 300 SD after many hrs. on tne road. The last road trip after about 6 hrs. of driving it starts fluttering to the high overheating range but am pretty sure engine is not running hot just erratic reading. Has any one else experianced this and where do you think the problem could lie? The sender, or gauge or wireing? Where is the sender located?

Engine ground strap.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Temp sensor/sender is on drive direction left, in the head. Test resistances across it at varying temperatures - should give you a quick sense of its functionality.

Also worth just plain cleaning the contacts on it - the sensor's post, and the plug's cylindrical connector. I also remember I broke my connector's plastic housing a few years back, just being un-careful. Dumb! But all very easy to fix.

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'83 300 SD
'68 Triumph TR 250 - The only car I ever loved more than the Mercedes; who needs electricity, anyway? - Damn, why did I sell it?!
'59 Jaguar 3.4 'Le Chat Noir' - Damn, why did I sell it?!

It's difficult to make predictions, especially about the future.
- Niels Bohr

I agree with VSTECH, ground Strap. The one between the engine and Body, remove it and clean the contact areas.
I had this same problem with our 85 300D.

Had replaced the engine with a rebuilt one painted up all pretty. Pretty doesn`t make a good ground. LOL
Scratched off some paint, and all was good.


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

what happens is the ground strap is connected with a transmission bolt, and the bolt strips. the HIGH amperage of the starter causes a temp welding connection, but as you drive a bit, the oil and grease loosen the connection, vibrations get the cable wiggling and it loses contact. grab the cable, and I bet it wiggles freely...
without engine ground, the ground on the instrument cluster, is a different value than the ground on the temp sender itself, and you get a weird high reading occasionally. The giveaway is the RAPID jump to high... no way for that to happen on an engine...

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

In extreme cases, a loose ground strap can burn out traces in the cluster and cause other strange problems (by the cluster ground supplying current to the starter due to the missing ground strap ground). This actually happened to me not long after I bought my first Mercedes (the 83 300D in my sig). Got it going within a day with help from this forum. Fix that ground strap quick!

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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

My temp sender wire was broken had to rewire mine.Yes I clean ground strap every few years,I also added a second one.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

Thanks for all responses I will check the ground strap 1st. Where can I find this on the 85 300 sd? It sounds like this could be the problem.

You're looking for a short thick black wire that runs between the engine and the body. (Don't be afraid to crawl underneath and investigate
) Mine was on the driver side IIRC but i got rid of it and ran a wire directly from the battery's negative terminal to one of the starter bolts.

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General George - 1967 Land Rover 2a SWB 1983 OM617 Turbo

I finally got around to check out the ground cable and sure enough it was very lose on the end that was secured to the starter on the bell houseing on the passenger side of the motor. I took the ground strap off totally cleaned both ends and tightened back on now temp. Gauge is reading normally and not bounceing around problem solved. Thanks for all the replies now to get on with other issues with this car.