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  #1  
Old 03-16-1999, 08:38 PM
donwo
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The temp gage on my 87 300e constantly reads higher than the actual outside temp by 10 degrees or so. Is this normal? Where is the sensor locacted and is it easy to replace?
Thanks I
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  #2  
Old 03-16-1999, 09:48 PM
M.B.DOC
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THE TEMP. SENSOR IS POSITIONED ON THE
FRONT BUMPER JUST BEHIND THE LICENSE PLATE
MOUNTING BRACKET. IF THE SENSOR HAS BEEN DAMAGED OR MOVED TO ANOTHER LOCATION IT COULD ACCOUNT FOR ERROR IN CALIBRATION.
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  #3  
Old 03-17-1999, 01:56 AM
Benzmac
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I have seen the sensor misplaced usually towards the radiator(a hot area) cause this problem.
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  #4  
Old 03-17-1999, 09:09 PM
Ken
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The temperature indication is very sensitive to sunlight shining on your license plate, especially when sitting (the airstream usually cools the license plate quickly after you start driving), but if you drive into the sun (and depending where you live -- e.g., Florida, Arizona?) your sensor may read higher than a properly shaded meteorological thermometer (viz., your radio's weather reports).
On the other hand, your temperature sensor may be damaged or defective and need replacement.
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  #5  
Old 08-01-1999, 02:13 AM
Robert W. Roe's Avatar
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May I ask how and exactly where this sensor should be mounted? I just got an '84 300SD and the silver-gray wire was hanging down below the license plate. I pushed it back behind the bumper but I want to mount it properly to avoid damage.

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Robert W. Roe
1984 300SD 164K miles

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  #6  
Old 08-01-1999, 10:38 PM
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It is usually connected to the rear of the front tag.

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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
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  #7  
Old 08-21-1999, 07:50 PM
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The temperature gauge on my 1987 300D is not working at all - no LCD. How do I replace this?
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  #8  
Old 08-21-1999, 09:13 PM
rego
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Mine is not working either. 86 300E The dealer wants $240 for the part in the dash. That is a little steep. It looks like my LCD was over heated or bent. Larry
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  #9  
Old 08-21-1999, 11:03 PM
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With M. Benz pushing harder & harder for their major parts vendors (VDO in this case) not to do business with the aftermarket prices will rise higher!! Just as with your outside temp gauge. If you had a new car w /digital dash then the complete instrument cluster would need replacing.

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190E 2.3 ITS RACECAR


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  #10  
Old 11-01-1999, 10:01 PM
Barrie
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If your outside temperature gauge is not working the fault is most likely with the sensor unit. You can test both the sensor and display by connecting a 3,000 ohm resistor in place of the sensor. If the display is working properly then your gauge (with power on) will give a readout of approx. 77 degrees F (or 25C if you have a celsius gauge).
Having verified that the fault is with the sensor, you need only replace the sensor thermistor (about $5). However, M-B sells only the complete cable assembly (the sensor at the end of a long piece of wire, for about $50), which requires about 2 hours to route - hence the $200 cost. To minimize this labor some mechanics will buy the assembly, cut off the end, and splice it into the old cable. Spliced connections, particularly in the engine compartment, are not a good idea! Instead, you can easily replace the sensor yourself for $5 with no splices. Use a negative temperature coefficient (NTC) thermistor of 3k at 25C, such as Fenwal #192-302LET-A01 or Thermometrics #EC95F302W. They are readily available from any electronics supply house.
If you require more detailed procedures on testing or installation, post your questions and I'd be glad to oblige.
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  #11  
Old 11-01-1999, 10:31 PM
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Barrie, this is one good bit of info. Will you register? I want strong mechanical minds on this site!
Thanks again.

------------------
Benzmac:
1981 280GE SWB
1987 16V
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  #12  
Old 01-01-2000, 05:17 PM
tsuru
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Where is the other end of the lead running from the sensor? (Still waiting for my W124 CD). I want to test the system with the 3000 ohm resistor without trashing the sensor.
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  #13  
Old 01-01-2000, 06:34 PM
Barrie
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You have a number of options.
1)You can test the temp display part of the system by connecting the resistor to the input connector in the rear of the instrument cluster. If you get a good reading then the fault is either the sensor or the ground connection.
However, this test requires removal of the instrument cluster which is not a trivial task.
2)The sensor is much easier to get at, and most likely the problem; if not, its days are numbered anyway. There's no need to "trash" the sensor; just desolder one end of the sensor and clip the resistor across the two wires. At worst you'll destroy a $2 part if you screw up.
But it's your call. Let me know how you decide to approach it.
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  #14  
Old 01-02-2000, 07:53 PM
tsuru
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Isn't there a terminal block somewhere you can get to? MB ran the leads all the way from the sensor to the inst. cluster?

The guage always reads 136F. This would indicate no resistance, correct?

[This message has been edited by tsuru (edited 01-02-2000).]
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  #15  
Old 01-02-2000, 11:01 PM
Barrie
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Normally it's a straight shot, but you can verify that by tracing the wire from the sensor through the left-side harness to the instrument cluster.

The sensor is an NTC (negative temperature coefficient) thermistor. Consequently, your excessively high reading means that the thermistor's resistance is lower than it should be.

You can be quite confident that the sensor is bad -- and it's very simple to replace. In trying to be helpful, sometimes our descriptions make the job sound more onerous than it really is.

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