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Old 07-04-2002, 12:30 PM
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Join Date: Mar 2002
Location: Oregon
Posts: 28
Locating Coolant Temp Sensor on a M104

I'm trying to get a positive ID on the B 10/8 Coolant Temperature Sensor on my '90 300CE to do the Aux. Fan turn on point modification. The MB Electrical Troubleshooting Manual gives a location of the cylinder head. A picture in the manual shows it in close proxity to an injector. The manual does cover years '86 to '92 with other models so I suspect the picture could be from any one of them. Please see attached pic. Thanks
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Locating Coolant Temp Sensor on a M104-300ce_tempsensor_b108_pics.jpg  
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Old 07-04-2002, 12:37 PM
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Join Date: Aug 1999
Location: Florida / N.H.
Posts: 8,768
The 2 wire connector blue one .
The single wire one is for the gauge and the one that goes in sideways is the one for Engine management.
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Old 07-04-2002, 01:06 PM
Join Date: Dec 2001
Location: Southern California, U.S.A.
Posts: 8,503
That sure doesn't look like my 104.

It must be the CIS 104 in the in the 1990-1992 300CE, prior to HFM.
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".
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Old 07-04-2002, 06:46 PM
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Join Date: Mar 2001
Location: Evansville WI
Posts: 9,616
OK, I looked through the wiring diagram in the CD. In the diagram, the 2 wires that run to it should be:
One is Brown with a yellow stripe
One is blue with a grey stripe
Should be easy to find it by this method.

Last edited by Gilly; 07-04-2002 at 07:14 PM.
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Old 07-04-2002, 07:21 PM
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Join Date: Aug 1999
Location: Florida / N.H.
Posts: 8,768
B-10/8 is the blue one. Br/yl-bl/gy.
The other is also a 2 wire for ECU.
The 4 prong for 104s came out in 94 and replaced these two into the single case you mention...
The date change over was mid-production and is noted in the E320 schematic...
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Old 07-05-2002, 08:10 AM
Join Date: Mar 1999
Location: Tucker, Ga USA
Posts: 12,153
This switch will activate the aux fans when the engine temperature gets upto 107C.
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Old 07-07-2002, 12:26 AM
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Join Date: Feb 2002
Location: St. Louis, MO
Posts: 340
Location of Coolant Temperature Sensor

I asked the location of this sensor before. Car is '97 E320 (straight six). I know there is a single wire sensor in the thermostat housing. I'm assuming that is the one for the guage. I'm looking for the one read by the engine maqnagement system.
Somebody responded that it was on the rear of the block. I can't locate it from the top. Do you have to go at it from underneath? How many wires are connected to it and do you know their colors/functions? Thanks.
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