Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   PeachParts Mercedes-Benz Forum > Mercedes-Benz Tech Information and Support > Diesel Discussion

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 09-14-2015, 10:10 AM
Gene
 
Join Date: Mar 2007
Location: Buffalo NY
Posts: 1,102
Another erratic temp guage - 95 606

Folks, after replacing the engine harness and both two pin temp sensors, the temp guage still acts erratically. Warms up fine, but once at temp will creep up to 120, drop back to 100, and basically jiggle around. It will often settle at below 100 ( bet 100 and 80) once its being driven more than 30 minutes.

Engine does not appear to be overheating at all ( just changed the GPs so had to run engine at idle to warm it a few times) .

Question: will a bad ground at temp sensor in dash also cause the fans to turn on? I finally disconnected the new aux fans as they were coming on unneccesarily . Nor can I finish the AC system fix with the fans always on. So temp guage - signal must be fixed before next summer!

Every other 606 I've had went to 80 and held like a rock, only rising after coming off a long highway pull.

Thank you for any input! ( btw, I did not replace the four pin sensor - maybe I ought have?

Reply With Quote
  #2  
Old 09-14-2015, 12:12 PM
Diesel Preferred
 
Join Date: Oct 2007
Location: Charleston SC
Posts: 2,788
Test by measuring the actual engine temperature vs. the gauge. A non-contact thermometer from Harbor Freight is about $25 or so and perfect for troubleshooting problems like this.
__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC
Reply With Quote
  #3  
Old 09-14-2015, 01:31 PM
Registered User
 
Join Date: Nov 2010
Location: TX
Posts: 3,978
test the sensor resistance from the square wiring plug near the glow plug relay, it has the wires from the 2 pin sensor that is near cyl 6, one of the two pins run the gauge, and one goes to the glow plug controller.

The fans kicking on high for no reason (at least for me) was (what I think) a bad solder joint in the pushbutton control unit - as I replaced mine with another part I bought from a jyard.
__________________
2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)
Reply With Quote
  #4  
Old 09-14-2015, 02:37 PM
Diesel Preferred
 
Join Date: Oct 2007
Location: Charleston SC
Posts: 2,788
Zulfiqar,

Do you know the sensor resistance values, or are they published in MB literature?
__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC
Reply With Quote
  #5  
Old 09-14-2015, 03:10 PM
Registered User
 
Join Date: Nov 2010
Location: TX
Posts: 3,978
Quote:
Originally Posted by Maxbumpo View Post
Zulfiqar,

Do you know the sensor resistance values, or are they published in MB literature?
they are published in the literature.

they are the same values as the pre glow temperature sensor, there are two pins, each pin is a separate sensor referenced to ground of the cylinder head.

20C = 2.5 kohms
30C = 1.7 kohms
40C = 1.1 kohms
50C = 830 ohms
60C = 600 ohms
70C = 435 ohms
80C = 325 ohms
90C = 245 ohms
100C = 185 ohms.


so you can deduce from here that your gauge going to 120C shows that your wire is shorting to ground somewhere
__________________
2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)
Reply With Quote
  #6  
Old 09-15-2015, 06:31 AM
Gene
 
Join Date: Mar 2007
Location: Buffalo NY
Posts: 1,102
Thnx folks, An infrared therm is next step. Z thank you for the info. The GP harness is brand new, ( original harness replaced) which I thought would cure the issue. Then there was the collapsing upper radiator hose. And then both two pin sensors were replaced. Only the four pin remains as factory.

Yet, there is no other evidence of a failed pump or thermostat. I beleive it all electrical. Temps were at over 100 when I got home. Upper hose was warm to touch, intake mani was still near cold! This morning after a five minute run, 120, but the upper rad hose wasn't even fully pressurized and intake still cold! AAAARRGH!

Good news is I have until next spring to fix it , replace the condensor and recharge the AC.

Given that the wiring harness is brand new, where would the short be? It does trigger the aux fans, which is why the brand new aux fans are now unplugged. This leads me to believe it's not the guage ground itself.

These old "simple" diesels are not so simple to diagnose, are they!?

Last edited by WINGAS; 09-15-2015 at 07:00 AM.
Reply With Quote
  #7  
Old 09-15-2015, 12:09 PM
Registered User
 
Join Date: Nov 2010
Location: TX
Posts: 3,978
Quote:
Originally Posted by WINGAS View Post
Thnx folks, An infrared therm is next step. Z thank you for the info. The GP harness is brand new, ( original harness replaced) which I thought would cure the issue. Then there was the collapsing upper radiator hose. And then both two pin sensors were replaced. Only the four pin remains as factory.

Yet, there is no other evidence of a failed pump or thermostat. I beleive it all electrical. Temps were at over 100 when I got home. Upper hose was warm to touch, intake mani was still near cold! This morning after a five minute run, 120, but the upper rad hose wasn't even fully pressurized and intake still cold! AAAARRGH!

Good news is I have until next spring to fix it , replace the condensor and recharge the AC.

Given that the wiring harness is brand new, where would the short be? It does trigger the aux fans, which is why the brand new aux fans are now unplugged. This leads me to believe it's not the guage ground itself.

These old "simple" diesels are not so simple to diagnose, are they!?
the wiring to the 2 pin sensor to the back of the cylinder head is part of the main engine wiring harness not the glow plug harness.

If you remove the crossover pipe you will see a small wiring loom going from the main to the driver side of the car to a small square plug, that plug is where the temperature sensor for the gauge, the preglow and the 2 wire sensor at the very front of the cylinder head patch into the body wiring.

The round temperature sensor goes to the ELR and EGR control units behind the battery - bundled in the main engine wiring harness.

btw - the upper radiator hose collapsing is not anything to be alarmed of, its also proof that the system is airtight, the expansion tank cap requires some amount of negative pressure to open its relief valve. This can cause the hose to collapse. It did that on mine too, no problems at all.
__________________
2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)
Reply With Quote
  #8  
Old 09-20-2015, 08:20 AM
Gene
 
Join Date: Mar 2007
Location: Buffalo NY
Posts: 1,102
Thank you Zul. I havent chased it down yet, as I know its not overheating. Odd thing is after some runtime, like 2 hours, the guage seems to settle in and work fine. 6 hours of runtime yesterday and it was reading fine for the final 4. ?

Changing the upper rad hose did nothing so... quite right!

Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On




All times are GMT -4. The time now is 01:03 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2024 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page