What is the first sensor to the right of the dipstick? The second one to the right is for the coolant temp gauge I believe. A quick search through the FSM wiring diagram turned up nothing.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

California or Federal? Could be something unique to the California models, but that's just a guess.

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Never be ashamed to ask for help.

1985 300D
1987 300SDL
1970 Jaguar E-Type OTS
2002 Dodge Intrepid (Traded In)
2011 Ford Crown Victoria

Federal.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I'd guess it is also a water sensor - I can't see what else it could be.

Where does the wire go? (Follow the bear)

Is it some sort of electro vacuum when the engine is cold thang?

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

quite certain thats the temp sensor for the emissions system.

It works at a different range of resistance than the gauge sensor and you'll know when they're placed incorrectly.

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It's a coolant sensor. #83 in the following diagram

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Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

Thanks! That's the diagram I was looking for in the FSM CD I have but couldn't find it in 85 300D turbo. Where in the FSM is it?

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

You won't find it. I scanned and posted those '85 diagrams from my 1985 model year specific supplemental manual.

And that coolant sensor is very important for the transmission to shift properly and for the emissions equipment.

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1983 123.133 California
- GreaseCar Veg System

Thanks for scanning it! It's been invaluable many times over.

I don't understand how it's connected to the transmission for shifting properly. Can you explain?

Thanks again.

__________________
Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

Yup, a water temp sensor for either the dash gauge or the EGR computer.

-J

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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.

I haven't seen the FSM, but I have been told by several independent sources that one sensor is for the gauge, whereas the other water temp sensor is just a temperature switch directly related to the glow plug duration. I could be wrong, but I do know first hand you cant switch them around and have your gauge work.

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1985 MBZ 300D (DD, 240k, unmuffled hellion!)
1982 MBZ 300D (372k, retired for parts)
1981 MBZ 300D (575k, parts pig)

When I was having an over heating problem according to the gauge, my Indy mentioned to swap the two wires to see if the gauge changed, then I would know it could be the sensor. from that I thought they were the same Sensor, could be used in either hole.

Swapped the wires and the gauge read the same. was another problem I finally chassed down


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

Some cars use a coolant switch to change vacuum solenoids for the shift firmness.

-J

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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.

I took a quick resistance reading of both sensors with a DVM and the sensor on the right (temp gauge) has approx 10x higher resistance than the one on the left (EGR control). So on my 85, I'd say they are not interchangeable.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Yep. I didnt measure with the ohmmeter, but I learned it when the parts guy gave me the wrong one and my dash gauge went from reading a bit off to not working at all. I did it the hard way by trial and error.

Now, this might only pertain to the 84.5-85MY that use the EGR computer mess.

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1985 MBZ 300D (DD, 240k, unmuffled hellion!)
1982 MBZ 300D (372k, retired for parts)
1981 MBZ 300D (575k, parts pig)