Can somebody tell me the location of the coolant temp sending unit.
I'm having trouble with my temp gauge jumping and I want to replace it.
1987 300D #14 Head 270k miles.

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1987 300d
1966 Jeep cj6 Perkins diesel
1966 Sunbeam Tiger
1979 Jeep cj7
1998 Subaru Forester(wife's car)
1988 Dodge Pickup

The coolant temp gauge sensor is B13, located on the left side of the engine below the intake manifold, forward of the IP and in between a couple of the glow plugs.

The sensor "forward of where lower radiator hose connects to engine" is the 50C temperature switch that operates the transmission vacuum solenoid.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

... on the W124. The W126 doesn't have that system. On my car that temp sensor is used by the climate control system for overheat protection, which turns on the rad fans to high speed and also shuts off the AC progressively.

-Jason

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

OK, so which car does the OP have?

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

He's got the W124 based on his profile.
Gee, why is it again we ask for year and model of car????

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Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

Thanks guys I edited my original post with the year make and model of my car, this jumping temp gauge is driving me nuts and unfortunately that gauge sender is in a really bad place, I was able to just barely get a finger in there to move the wire, to maybe give it a better connection if that's the problem. I'll take the car out for a ride later and see if it is still happening.

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1987 300d
1966 Jeep cj6 Perkins diesel
1966 Sunbeam Tiger
1979 Jeep cj7
1998 Subaru Forester(wife's car)
1988 Dodge Pickup

Let's slice W126s a little finer. 86-87 SDLs have the 50*C temp switch by the thermostat. 90-91 350SD/Ls don't. W140 Diesels don't.

Sixto
87 300D

I would probably remove the IM to pull that sender; others might depend upon a collection of adapters and u-joints to pull it with the IM in place.

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

If it isn't fixed by the wire jiggle, and odds are it won't, try running a separate ground wire "from" the frame back behind the instrument cluster "to" the back metal plate of the instrument cluster somewhere. Almost any screw location will work.
This has fixed many a persons jumping gauges.....

__________________
Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John