I'm curious whether anyone has published data points or an equation correlating resistance vs. temperature for the engine block coolant sensor for a W123 300D-T.

That's basically the end of the road for my reckless replacement of cooling system parts (two degrease/acid flushes, new validated t-stat, new radiator, water pump impeller inspected), and I'd like to know what the resistance should be at a given temp before I spend even more $$ for a new one(yeah, I know I shoulda looked here first). I still run 100+ when running up a hill on the highway. The reason I hadn't considered it an instrument issue is that it settles around 84C when overrunning down a hill on the highway, and that is where I validated the t-stat to start opening on the stovetop, and is published at 84C in the shop manual.

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Dave

2002 Audi S6 Avant
1983 300D
1984 300D (sold)
1990 560SEL (sold)

what car we talking about here ? are you talking about the sensor that has a 4 prong (round) on it ?

Sorry, W123 300D turbo.

Attached Thumbnails

 

__________________
Dave

2002 Audi S6 Avant
1983 300D
1984 300D (sold)
1990 560SEL (sold)

Infrared thermometer would confirm or deny the sensor's accuracy.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

http://www.kienzle.de/uploads/media/sensoren_instrumentierung.pdf
there is a cross-reference table ,find your VDO sensor number---should be 51ohm@90 Celsius,I think....that`s the standart for many years...also:

http://www.motometer.de/pdf/sensoren_tempgeber_120_e_so.pdf
The resistance characteristic is
identical for all sensors:
60 °C 134 Ohm
90 °C 51.2 Ohm
100 °C 38.5 Ohm
your is analogue to MMeter 642 007 1018 40 – 120 °C M 14 x 1.5 6 – 24 Volt 21 mm Round connector 4 mm...

Good luck,the reference worked for me...
P.S.
http://www.detali.ru/cat/oem_mb2.asp?TP=1&F=123193&M=617%2E952&GA=722%2E120315&CT=M&cat=143&SID=20&SGR=015&SGN=01
it`s number 125
The VDO corrsep. number is 323-801-020-002D ,page 27 of the VDO.pdf,bottom....

I never knew that sensor information was published for these cars. As the original poster mentioned it sure beats buying sensors just on speculation. Thanks for digging the information out.
Have you done the required tests to determine your fan clutch is still in good condition?
I imagine if we had a chart of the top to bottom average temperature difference might be helpful as well. If enough btus are not being lost from the rad it would be reflected by closer inlet/outlet temperatures.
I used to consider that if the temperature fell signifigantly when going uphill with the heater at full blast then things especially the rad but in your case the air flow through it were suspect. A normally operating coolant system requires no help to maintain a fairly tight range of gauge readings. There are hills and then there are hills.
My second thought is if the engine is the 617 series and you do not actually blow coolant out ever it is not going to hurt anything. I would just drive it and see if the condition was stable or worsening. Also if the temperature gauge swing and temperature indications are remaining exactly the same in lower ambient temperatures it probably is not the air flow.
Just my opinions and their application depend somewhat on your prior experience in this area. Plus your ability to discern the results correctly. Marginal problems are occasionally as hard to run down as intermittent ones.

The sender is so cheap if it is more than 5 years old and you think there may be a problem, replace the sender.

unless your cheap and have the correct tools .. its nice to eliminate a part for free and not wonder if that was really it or not

COOLANT TEMPERATURE SENSOR (B11/9 or B11/10) RESISTANCE

At -20 °C 15.7 kOhm
At -10 °C 10.0 kOhm
At 0 °C 5.9 kOhm
At 10 °C 3.7 kOhm
At 20 °C 2.5 kOhm
At 30 °C 1.7 kOhm
At 40 °C 1.17 kOhm
At 50 °C 830 Ohm
At 60 °C 600 Ohm
At 70 °C 435 Ohm
At 80 °C 325 Ohm
At 90 °C 245 Ohm
At 100 °C 185 Ohm
Tolerance ±5%

I believe the one in your thumbnail is this one. If so, I just replaced the same one in my 1984 300SD. The values above are from autozone's online manual for my model.

Only 100+? If I run mine at 65 mph for more than a few minutes, I peg the needle out on the meter past the red...Consider yourself lucky that your car cools at all.

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1983 Mercedes-Benz 240D
Automatic, A/C, Power Sunroof, Power Right Side Mirror
231K Miles FOR SALE MAKE OFFER

You're not going to get away with doing that too many times.

65 mph? wow... you have some serious cooling issues.

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Have you ever noticed that anybody driving slower than you is an idiot, and anyone going faster than you is a maniac?

As long as they would add one additional commandment for you to keep thy religion to thyself.
George Carlin (Wonder where he is now..)

1981 240d (engine donor 1983 240d) recently rebuilt engine hurray! - No more.. fought a tree and the tree won.

pearl black 1983 240d 4speed (Converted!@$$%) atleast the tranny was rebuilt.

Update:

I swapped sensors from my other 617.952 car that runs perfectly with no difference.

I then swapped the thermostats, and voile! It was that stinking thermostat all along! I even replaced it with one from worldpac two years ago when I first realized I had a problem. The new one from the mb dealer that I put in the donor car now runs hotter too...but it's a steady 90-95C instead of the 100+ creep I was experiencing with the other car.

__________________
Dave

2002 Audi S6 Avant
1983 300D
1984 300D (sold)
1990 560SEL (sold)