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Old 07-11-2002, 04:41 PM
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Join Date: Jun 2002
Location: Monrovia, CA
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300E - Coolant Temp Sensor: Where is it?

I need to find my coolant temp sensor on my '86 300E, the one that triggers the aux. fan (I want to bridge it with a resistor to make it come on at a lower temp) - would someone please tell me where it is and what it looks like? What color are the wires going to it or what color is the plastic part of it?

Also, is there any accurate way to test it without special tools? It seems to be triggering the fan a bit late - about 110C by the dash gauge.



Last edited by Phalcon51; 07-11-2002 at 05:24 PM.
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Old 07-11-2002, 04:46 PM
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Join Date: Feb 2002
Location: St. Louis, MO
Posts: 340
Me too, but on '97 E320

Hard to get a definitive answer on this. One responder said rear of block. Aanother said front on/near water pump. I can't see anything but the one for the temperature indicator. i'm looking for the one that the engine management system uses. Thanks.
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Old 07-11-2002, 06:33 PM
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'94 S500: only 793 sold!
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Check this picture. . .

If you want a 'pro' version, check my page!
Regards . . . . JimF
'94 S500 Cpe

Visit my Mercedes Web Page
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Old 07-12-2002, 12:09 AM
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Location: Monrovia, CA
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Thanks for the pic. In that location, I've got a similar looking device, except that it has one 2-wire plug and a 1-wire plug. Any idea what the extra lead is for? Can I still bridge the 2-wire connector with a resistor to effect a lower aux. fan trigger point?


Last edited by Phalcon51; 07-12-2002 at 01:03 AM.
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Old 07-12-2002, 12:26 AM
pmizell's Avatar
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Join Date: Jun 2001
Location: Houston, Texas
Posts: 838
The coolant temp sensor has moved around on the M103 engine, depending on model year. On your '86 model, it is located at the rear of the head, last sensor before you hit the firewall and it looks like this:

Have a nice day,


'91 300E, 215K miles
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Old 07-12-2002, 12:46 AM
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Posts: 2,357

According to an old post here, there are actually THREE coolant temp sensors. I believe the one that JimF circled above in the photo is for controlling aux. fans. Please see the following thread:

1986 300E coolant temp. sensor!
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
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