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  #1  
Old 03-28-2008, 04:55 PM
Blevinsax's Avatar
'91 350SD GreaseCar
 
Join Date: Jun 2006
Location: Las Vegas, NV
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Question Temp gauge not working properly... help?

Okay - this is starting to get on my nerves...

I took the car to Sig's ******** (the only Mercedes shop in Las Vegas that I've seen mentioned on this forum) for some work because I want to get all the bugs worked out before my daughter is born in June. He did a good job on most everything, but when I picked up the car the temp gauge was not working properly. I thought the car was running cool because the temp gauge only read 60-70C, but the car is actually running at proper temperature - it is the gauge that is not reading right. By the next day the temp gauge was completely dead - pegged at the bottom. He just replaced the temp switch (on the manifold between 2nd and 3rd cylinders) but the gauge is still reading low while engine temps are normal.

Any idea what else might be causing this problem? Thanks for the help in advance! I hate having to do research for my mechanic - I just wish I could find someone local who is really knowledgeable.

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Autos:
1991 350SD 276,000 miles
2001 VW Beetle TDI 115,000 miles

Horns:
1955 Selmer Mark VI Alto (55,xxx)
1958 Selmer Mark VI Tenor (85,xxx)
1964 Selmer Mark VI Tenor (125,xxx)
1967 King Super-20 Tenor (430,xxx)
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Last edited by Blevinsax; 03-29-2008 at 11:57 AM.
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  #2  
Old 03-28-2008, 05:27 PM
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I would suggest pulling another gauge from a diesel W126. I don't think the ones from the 85 and older diesel W126s will work, since the newer W126 diesels have little lights that give ABS warnings and low windshield washer fluid level warnings.
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  #3  
Old 03-28-2008, 05:31 PM
Blevinsax's Avatar
'91 350SD GreaseCar
 
Join Date: Jun 2006
Location: Las Vegas, NV
Posts: 480
Obviously I could be wrong, but I am not sure the gauge is at fault. If the gauge is grounded, the needle pegs at 120. It just does not read correctly from the temp sender.

Could it have something to do with low coolant level? When I started the car the evening after I picked it up, the coolant was low because of my greasecar system - all the air pockets filled and the coolant was low. I filled the coolant tank and it seemed to be okay, but I wonder if it could be related...

Any thoughts?
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Autos:
1991 350SD 276,000 miles
2001 VW Beetle TDI 115,000 miles

Horns:
1955 Selmer Mark VI Alto (55,xxx)
1958 Selmer Mark VI Tenor (85,xxx)
1964 Selmer Mark VI Tenor (125,xxx)
1967 King Super-20 Tenor (430,xxx)
2002 Selmer Series III Soprano

For Jazz Saxophone enthusiasts - check out my website...
www.RustyBlevins.com
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  #4  
Old 03-28-2008, 05:33 PM
pawoSD's Avatar
Dieselsüchtiger
 
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Location: Grand Rapids, MI
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Quote:
Originally Posted by Blevinsax View Post
Obviously I could be wrong, but I am not sure the gauge is at fault. If the gauge is grounded, the needle pegs at 120. It just does not read correctly from the temp sender.
Try another temp sender....sometimes senders go bad right away. I had a brand new oil pressure sender go completely dead in 2 days.
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  #5  
Old 03-28-2008, 05:51 PM
Blevinsax's Avatar
'91 350SD GreaseCar
 
Join Date: Jun 2006
Location: Las Vegas, NV
Posts: 480
Could it have something to do with low coolant level? (See my previous thread) When I started the car the evening after I picked it up, the coolant was low because of my greasecar system - all the air pockets filled and the coolant was low. I filled the coolant tank and it seemed to be okay, but I wonder if it could be related...
__________________
Autos:
1991 350SD 276,000 miles
2001 VW Beetle TDI 115,000 miles

Horns:
1955 Selmer Mark VI Alto (55,xxx)
1958 Selmer Mark VI Tenor (85,xxx)
1964 Selmer Mark VI Tenor (125,xxx)
1967 King Super-20 Tenor (430,xxx)
2002 Selmer Series III Soprano

For Jazz Saxophone enthusiasts - check out my website...
www.RustyBlevins.com
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  #6  
Old 03-28-2008, 11:44 PM
Blevinsax's Avatar
'91 350SD GreaseCar
 
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Location: Las Vegas, NV
Posts: 480
Any thoughts?
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  #7  
Old 03-29-2008, 12:18 AM
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On my 85 617 there are 2 temp sensors on the left side of the engine between the # 1 & #2 glow plug and one between #2 & #3 plug. one is the temp sender & the other is for the temp sender for the glow plugs.
switch the wires, both senders wouldn`t be bad.

Don`t know about the 91 350, so just a guess.

Charlie ☺
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  #8  
Old 03-29-2008, 11:58 AM
Blevinsax's Avatar
'91 350SD GreaseCar
 
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Anyone else have an idea?
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  #9  
Old 03-29-2008, 12:05 PM
Unofficial wormcan opener
 
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Location: Ashland, MA
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Are you sure the correct sensor was replaced?
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  #10  
Old 03-29-2008, 08:23 PM
Blevinsax's Avatar
'91 350SD GreaseCar
 
Join Date: Jun 2006
Location: Las Vegas, NV
Posts: 480
Quote:
Originally Posted by Bio300TDTdriver View Post
Are you sure the correct sensor was replaced?
Yes - when the two contacts on the back of the sensor/sender are grounded, the temp gauge spikes to 120, so I am sure we are working with the correct sensor/sender. Neither the gauge nor the circuit are the problem - the sensor/sender is just not sending the temp to the gauge.
__________________
Autos:
1991 350SD 276,000 miles
2001 VW Beetle TDI 115,000 miles

Horns:
1955 Selmer Mark VI Alto (55,xxx)
1958 Selmer Mark VI Tenor (85,xxx)
1964 Selmer Mark VI Tenor (125,xxx)
1967 King Super-20 Tenor (430,xxx)
2002 Selmer Series III Soprano

For Jazz Saxophone enthusiasts - check out my website...
www.RustyBlevins.com
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  #11  
Old 03-29-2008, 11:22 PM
Unofficial wormcan opener
 
Join Date: Dec 2005
Location: Ashland, MA
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Quote:
Originally Posted by Blevinsax View Post
Yes - when the two contacts on the back of the sensor/sender are grounded, the temp gauge spikes to 120, so I am sure we are working with the correct sensor/sender. Neither the gauge nor the circuit are the problem - the sensor/sender is just not sending the temp to the gauge.
OK, you are working with the correct sender location. How do you know the correct sender is in the location that you grounded? I thought it was sending a temperature, just the wrong one. Which would lead me to believe you are using a sender that is defective or the incorrect sender, or something else is changing or corrupting the signal. How is the wiring from the sender to the gauge? Is it possible that the casing on 2 wires are broken and they are touching?
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1987 300TD 309, xxx 2.8.2014 10,000 mile OCI


Be careful of the toes you step on today, as they may be connected to the ass you have to kiss tomorrow. anonymous

“Be who you are and say what you feel, because those who mind don’t matter, and those who matter won’t mind.” Dr. Seuss
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  #12  
Old 03-29-2008, 11:42 PM
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Location: So. California
Posts: 744
Maybe someone out there can measure the resistance of their sending unit when the engine is cold and when its at full operating temperature.

Then Rusty, you ought to also measure yours. Then compare.

Eric
(Sax content: Eric, whose F.I.L. played with Louis Prima for 15 years)

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