The temperature gauge in my 1980 300sd is bouncing all over the place. Is this most likely due to a faulty sensor or a bad gauge?

Thanks

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DCM

1977 240d
1980 300sd
1987 Chevrolet Suburban

My bet is bad wire.
also could be a fuse.
John

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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!

My money is on a faulty ground to the gauge cluster.

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

Does your fuel gauge do it also? Mine does, and I know I have to pull the cluster and reinstall it. Both shake in snyc, looks kind of freaky.

a swift slap to the dash fixes mine

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commercial fisherman diesel in my blood in my boats trucks and Dear old Dad has had me drivin them since i got my first license in 1968
1986 300 SDL 427654
1999 Chevy Crew Cab Dually 225423
1986 300 SDL 287000 Dad's
1987 190 Turbo 158000 Mom's (my inheritance)

If it is the only guage giving you problems, I'm betting on a loose/corroded connection at the sensor. If there are other problems, check your eng-chassis ground.

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Sam

84 300SD 350K+ miles ( Blue Belle )

A while ago a forum member talked about fixing a jumpy fuel and OP gauge by running a new ground from the back of the instrument panel. I fixed my jumpy gauges by doing that a couple days ago, evedently bad grounding was the problem in my case..

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

Edit: This is on a 1985 300TD w123/123.
I wanted to add some input on this issue. My fuel gauge and temp gauge were both going crazy, bouncing when I turned on my headlights. If I put the car in neutral sometimes they would go back to accurate reading. When put back into gear (reverse or drive) they would bounce again. I thought I had a pinched wire due to the transmission being replaced. After searching this forum I found a ton of threads that lead to fairly simple solutions. I checked my battery ground, cleaned/sanded and reconnected. I checked my engine/chassis ground, cleaned and reconnected. I opened up my instrument cluster and was intimidated by the many wires coming out of the back. Someone in one of the posts on this suggested making a new ground rather than tracking down a bad one. I wanted to show people an easy way to do this. On the center back of the instrument housing the Oil Pressure, Tempurature and Fuel gauges there is a small threaded stud/nut sticking out about 1/4 inch or more. I attached a (green in pics) copper ground wire from this down 1 of the 2 grounding areas directly behind and below the instrument cluster. It's as simple as that. Use caution pushing out your cluster making sure wires/cables are free. There's also some insulation that simply folds over.
You could also check your ignition vacuum supply/shutoff hoses while your in there. Look up from directly under the backside of the key tumbler and see if the two hoses are swollen or wet. If so they'll eventually cause some problems with the car not shutting off...