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560SL Coolant Temp Sensor

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ericml's picture
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Hi guys.  I'm having an issue with my 560sl running warm or at least that is what the gauge is telling me.  I think the coolant temp sensor may be bad.  I was on the EPC and it looks like there is just the one “sender unit” with part number A 005 542 10 17 or A 005 542 26 17.  Upon inspecting the car it looks like there is another sensor right next to what I believe is the CTS.  This other sensor has 2 separate wires connecting to it.  One wire connected to that sensor has 2 prongs and the other has 1.  What sensor is this and what sensor is actually the coolant temp sensor?  A part number would be great too if possible.  Thanks in advance!

Eric
 

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  • 1987 560SL - 54k, bought May 2010 
  • 2000 Chevy S10 Ext Cab - 66k
  • 2003 Saturn Ion Coupe - 37k
  • 2005 Yamaha Vino 125 Scooter - 2k
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gerryvz's picture
The Woodlands, TX
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1995 E320 Wagon
1994 E500
1990 560SEL
1989 560SEC
I wouldn't say that these

I wouldn't say that these temp sensors go south all that often.

A photograph or two of the items you are referencing would be helpful.

An inspection of the cooling system (and various related parts) with a handheld digital thermometer can be revealing as to the accuracy of the sensor, so I'd confirm the general accuracy of your temp sensor that way.  I believe there is also a test you can do with a multimeter to determine the sensor's output electrically (different characteristics depending on the sensed temp).  That should be in the service manual for the car (not the owner's manual).

If the indicated temps are good, and the reading is indeed accurate, then you may want to look into seeing of you have cooling system issues.  Quite often the fan clutch goes bad, requiring replacement.  On the M117 they are not exorbitantly expensive -- I do recommend the factory unit, not aftermarket, for this part.

Another item that can contribute to warm temperatures is an inefficient radiator (a common "wear" item). More detective work would be a good thing.

Generally, if things are in good working order, you'll see temperators ranging between the needle sitting right ON (or just above) the "80C" mark and the hash mark that indicates 100C.  Often on a hot day, sitting in traffic, you can see things climb up to the 100C mark. If the cooling system is in good condition, generally things won't exceed the 100C hash mark on the gauge.  If you have an inefficient radiator or fan clutch in need of replacement, then things can often climb up to the 110 and even higher toward the 120F mark, particularly on a hot day.

Cheers,

Gerry

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abiby's picture
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I believe the

I believe the correct gauge sender is A 005 542 26 17.  It has one terminal.

However, like Gerry, I doubt it's a sending unit issue.  

Are you a new owner?  If so, you may just not be used to the way the temp gauge in your SL acts.  Low 80s to 100 are normal.  If you're not getting into the red area on the gauge you may not have an issue.

Also like Gerry said, failure of the viscous fan clutch to operate correctly is common.  

IMO though, the thermostat is a common issue, and since coolant is often neglected, yours is possibly due for replacement, and a new thermostat at the same time is always a good cheap investment.  BTW, if you're not aware, be sure to use the correct coolant, either MB or IIRCxerex g05.

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Tom Hanson's picture
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005-542-10-17 is the current

005-542-10-17 is the current number for the temp gauge sender. It's not uncommon for them to go bad, but usually the gauge won't read at all when they do. I'd need a picture of the other temp switch you're asking about to see what it is.

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Prior MB cars: 2010 ML350 Bluetec, 2003 C320 Coupe, 1986 300SDL, 1971 300SEL 6.3, 1973 450SE, 1959 220S, 2011 C300

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installed the new sensor

Well I picked up a new sensor (and a new MB hat haha) from the local dealer here.  Took the car for a drive in town to get it up to temps.  It stayed from about 90 to 93 the entire drive.  It's 78 degrees out and low humidity.  Am I in the ballpark for normal operating temp?  Thanks for all the responses too guys it's much appreciated!

Eric

 

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  • 1987 560SL - 54k, bought May 2010 
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1989 560SEC
Around 90 (perhaps a bit more

Around 90 (perhaps a bit more in warmer weather) is fine and sounds in the ballpark.

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thanks Gerry

Thanks Gerry.  I spun the fan by hand before the drive and after as well.  Before the fan spun freely by hand but after it spun only a few inches before stopping.  Does that sound like a healthy fan clutch?  Just took the car out again tonight on a short drive in town.  It' s a 62 degree night and the temps stayed right where they were last night - mostly about 90 but did hit about 93 and then back to 90 a couple times but it seems to want to stay at 90.

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  • 1987 560SL - 54k, bought May 2010 
  • 2000 Chevy S10 Ext Cab - 66k
  • 2003 Saturn Ion Coupe - 37k
  • 2005 Yamaha Vino 125 Scooter - 2k
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The Woodlands, TX
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1995 E320 Wagon
1994 E500
1990 560SEL
1989 560SEC
see this post (and thread) on

see this post (and thread) on my forum with regard to testing (& replacing if needed) the fan clutch.

http://www.500eboard.com/forums/showthread.php?1391-Viscous-Fan-Clutch-Replacement&p=10735&viewfull=1#post10735

Cheers,

Gerry

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update

Hi everyone.  I wanted to update you on the car.  I think it's finally fixed and it had nothing to do with the cooling system at all.  Every time I hit the turn signal my guages would "jump" as the turn signal clicked.  I had read on another forum that this was due to a poor ground.  I brought that up to my mechanic and he put 2 and 2 together.  Pulled the steering wheel, pulled the instrument cluster and fixed the bad ground.  The car is now sitting at about 82C and rarely moves from there.  She's fixed!  (fingers crossed)

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  • 1987 560SL - 54k, bought May 2010 
  • 2000 Chevy S10 Ext Cab - 66k
  • 2003 Saturn Ion Coupe - 37k
  • 2005 Yamaha Vino 125 Scooter - 2k

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