I've read the description of various ailments caused by a faulty coolant temperature sensor, and I'm beginning to think that it may be responsible for my cold & warm start trouble. Can anyone describe where this sensor is located on a W124 300E, and how I can test it? I've seached, but I only found vague descriptions...
Thanks guys!
Mika

I believe its on the thermostat housing.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record

Sounds like you're referring to the "Water Temp Sensor" a.k.a. "Temp Sensor for CIS". on my m103 (190e 2.6), it's on the top of the intake manifold, the closest sensor to the firewall.

If you're referring to the Temp. sensor for the temp. gauge in the cluster (probably not), it's also on top of the intake, the next-closest sensor to the firewall.

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1990 190e 2.6 - The only one I can really call "My Car".

1987 190e 2.3 - The donor car's up and running, only mods are Euros and a Sony headunit. My Dad's runabout now.

1990 300e 2.6 - The parents' ride.

OK, can anyone elaborate on how to actually test it, i.e. how many ohms over which terminals, etc.? My 300E has been having some issues lately and I would like to rule this sensor out.

Thanks.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

Ohm's range from the temp chart in the /Engine Manual-Combustion Manual-07.3 Mechanical/electronic gasoline injection system (KE injection)-121 Testing electrical components of KE injection system. page 60

Temperature °C........Resistance kΩ
-20........................15.7
-10.........................9.2
0............................5.9
10...........................3.7
20...........................2.5
30...........................1.7
40...........................1.18
50...........................0.84
60...........................0.60
70...........................0.435
80...........................0.325
90...........................0.247
Same resistance values apply to KE intake air temp sensor.
I think this chart applies to these 2 sensors for all KE systems but don't know for sure.

Is yours 2 prong? http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1FX0MB1RS1IG0SWQP6&year=1986&make=MB&model=300-E-002&category=C&part=Water+Temp.+Sensor&appEngines=_any
Just un plug it and measure the resistance across the 2 prongs, compare to engine temperature...

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-Marty

1986 300E 220,000 miles+ transmission impossible
(Now waiting under a bridge in order to become one)

Reading your M103 duty cycle:
http://www.peachparts.com/shopforum/831799-post13.html
http://www.peachparts.com/shopforum/831807-post14.html

2.8 kohms at roomtemp.

Glad to see you testing it before replacement. I think it's $50.


Michael

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Michael McGuire
83 300d
01 vw A4 TDI
66 Chevy Corsa
68 GMC V6 w/oD
86 300E

Hello

I have a 1987 300E

The car sat for over 1 day. I just went outside and pulled the two connectors off the sensor and I measured each point on the sensor (one at a time) to ground.

One of the points measured 1248 ohms and the other 1258 ohms. About a 8% difference so am not too worried that they both don't match 100%.

The outside temp was 68F or 20C

These values don't match the values listed in one of the above posts that lists Temp vs Resistance.

Actually I just reread the post and they measured it not each one to ground like I did but between the two points so 1248 + 1258 = 2506 ohms which matches the chart (20C = 2.5k)

Are we talking about the same senor? I am talking about the green sensor screwed into the top of the head closest to the firewall. The sensor that has the two individual wires/connectors.

Bosch part # 0280130044

wanted to confirm the above sensor is what this thread is about.

Also want to know if anyone knows how these fail, should I take more readings as the engine heats up?

The part is relatively inexpensive and easy to replace for peace of mind. If you want to bench test it. Run 2 long leads to the connector and connect the other ends to the sensor. Use a thermometer and you can either dip the probe end into water and take readings of the temp and resistance and note when the fans turn on.....or just use a heat gun and very careful heat the probe end for faster results. TBH, unless you're planning on modifying it, who cares about the values, readings/resistance, etc. As long as your fans turn on when the temp reaches the specified on value, I believe at 105°C, then you're good to go. Or you can simply get rid of that sensor and swap it for an on/off temp switch which will function the same way, minus having resistors/values to worry about.

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1990 190E 3.0L

thanks for the reply. I am talking about a different coolant temperature sensor. I am talking about the two prong temp sensor which is two sensors in one. One wire goes to the fuel injection control and the other sensor goes to the ignition control.

I care about if it is accurate as if not the ignition and fuel injection control systems will not have accurate inputs and therefore not manage the fuel and ignition systems properly.

You mention the radiator aux fan switch.

yes I will take a couple of more measurements as it warms up to see if the sensor is accurate at higher temperatures.

lsmalley - if I do end up changing the sensor do you know what size it is? I will most likely have to purchase a deep socket to remove it.

I believe it's 22mm

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1990 190E 3.0L