So, when I am driving my car my coolant temp gauge seems kind of strange. Sometimes it will sit right above 80 for the whole drive other times it will hang at 80 then kind of jump around up to 90 then up close to 100 then pop right be down near 80.

Is this the thermostat or is it a coolant temperature sensor or something like that. I want to make sure everything is working correctly with the hot months coming up.

Its a failing sender. Its in the cylinder head between the #2-3 glowplugs.

Is that a hard thing to fix? I mean can a home mechanic fix it, or do I need to take it to a shop to have it fixed? Also, if I was to buy the part myself, what type of sender is it? Does it have a specific name?

Again, kudos to this forum and FI. The SD I recently bought is doing exactly the same thing. Shot various places with an infrared temp gauge and the engine wasn't nearly as hot as the gauge indicated. I thought maybe it was a bad ground. Thanks FI

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John Schroader
bio burnin' 83 300D, '83 300 SD, '79 240D
"I've never met a man who was good at making excuses who was good at anything else" Ben Franklin
"You cannot permanently help a man by doing for him what he could and should do for himself" Abraham Lincoln

That's essentially what a bad sender is.

Water (or coolant) temperature sender.

My 300D does the exact same thing. The gauge moves but it advances much higher than the actual temperature and pegs the gauge before the engine reaches 80*C. My infrared thermometer shows 180-190*f across the cylinder head.

One wrench (or socket) and 3 minutes is all it takes. If you relieve the cooling system's pressure then reseal the cap (to stop airflow) you won't lose more than a few teaspoons of coolant.

i think my car is having this problem, so what is the part? i noticed one by the thermostat too, is it just the one between 2-3 cyl that sends info to the gauge? is it a coolant temp sensor? or is that particular piece called somthing else and how much does it usually cost?

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1985 mercedes benz 300D turbo diesel
1998 VW GTI VR6
1996 VW GTI 2.0
1999 saab 9-3 turbo
1987 300sdl (sold)

The one in the middle of the head sends temperature. The one on the thermostat housing is a cold-lockout switch for the blower.

The sensor costs $12-18 depending on where you get it.