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 07-03-2022, 02:20 AM
Registered User
 
Join Date: Jul 2022
Posts: 3
Gauges reading max

Hi guys,
Hoping for some information.
1984 Mercedes w123 300d

I had to replace the ignition steering lock assemble as the keys would no longer turn in the ignition.

I removed the under dash plastic panels, removed the dash gauges noted down where what went, removed the ignition assembly, noted which vacuum tubes went where removed the key buzzer wires etc.
Got the new lock assembly swapped the ignition switch, and the buzzer switch and diesel switch and put everything back where it came from started up and everything I thought was fine.

But then I noticed the fuel gauge reads full, oil pressure is up at maximum and the temp gauge creeps up as you would expect but just keeps rising to max. (Removed radiator cap and could hold finger in water was warm but not hot) lol I know silly but I knew it was not hot by the lack of steam.

I know there is only 1/2 a tank of fuel,
Oil pressure gauge use to sit about halfway
Temp gauge again normal sits about 1/2 way up.
But as I said they are now all reading max.

Pulled the dash out again just in case there was a wire I forgot to reconnect but everything looks like it was correctly reconnected.

Hoping someone has an idea, I don’t have another instrument cluster or access to one to try

Thanks in advance.

Reply With Quote
  #2  
Old 07-03-2022, 08:23 AM
t walgamuth's Avatar
dieselarchitect
 
Join Date: Apr 2005
Location: Lafayette Indiana
Posts: 38,609
Look for your ground on the cluster and clean it up or tighten it. When your gauges are acting squirrely look at your grounds.
__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.
Reply With Quote
  #3  
Old 07-03-2022, 08:51 AM
Registered User
 
Join Date: Sep 2013
Location: Alhambra California
Posts: 3,129
Good advice to check and clean the brown ground wires. You might consider installing a new ground wire from the back of the instrument cluster (there are several places to attach a ground wire) to the ground point on the steering column bracket. Worked for my 1985 300D when I had the same problem.
Reply With Quote
  #4  
Old 07-03-2022, 01:25 PM
vwnate1's Avatar
Diesel Dandy
 
Join Date: Nov 2005
Location: Sunny So. Cal. !
Posts: 7,717
Post Gauge Woes W123

Interesting as the oil pressure gauge is mechanical.....

I too would look at the grounds .
__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better
Reply With Quote
  #5  
Old 07-03-2022, 04:01 PM
Registered User
 
Join Date: Jul 2022
Posts: 3
Thanks guys,
The oil pressure gauge I thought strange as well,
Could I mount an earth from say the clock screws down to the earthing point or does it have to be from the PCB. I don’t really want to take the cluster apart.
Cheers
Reply With Quote
  #6  
Old 07-03-2022, 04:09 PM
Registered User
 
Join Date: Sep 2013
Location: Alhambra California
Posts: 3,129
A ground wire from a clock screw will work fine.
Reply With Quote
  #7  
Old 07-03-2022, 05:43 PM
Shern's Avatar
Semi-registered User
 
Join Date: Feb 2016
Location: Los Angeles
Posts: 1,806
Oil pressure gauge is indeed mechanical. Nothing to do with grounding.

You sure it isn't at half (1.5 bar?) after a highway run? Short drives around town and it should be pegged to 3 or very close to it.
__________________
1981 240D 4sp manual. Ivory White.
Reply With Quote
  #8  
Old 07-03-2022, 06:27 PM
Registered User
 
Join Date: Jul 2022
Posts: 3
I haven’t as yet taken it for a drive, just idling in the driveway, I’ll go into town today and pick up bits to run another earth.
With the cost of fuel here at the moment Driving the diesel would be advantageous.
Here in Australia $2.25 a litre, that’s about $9.00 a gallon.
Reply With Quote
  #9  
Old 07-03-2022, 07:06 PM
vwnate1's Avatar
Diesel Dandy
 
Join Date: Nov 2005
Location: Sunny So. Cal. !
Posts: 7,717
Post Ground Wires

Be sure to use a BROWN wire to match the rest of the D.I.N. spec. ground wires .
It needn't be thicker than 18Ga. and be SURE to test the ground path on the body tub proper .

Use a TEST LIGHT not a gauge .
__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better
Reply With Quote
  #10  
Old 07-06-2022, 08:27 AM
JHZR2's Avatar
Registered User
 
Join Date: Jan 2002
Location: New Jersey
Posts: 5,265
Quote:
Originally Posted by vwnate1 View Post
Interesting as the oil pressure gauge is mechanical.....

I too would look at the grounds .
Yeah that is throwing me off too…
__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)
Reply With Quote
  #11  
Old 07-06-2022, 11:09 AM
psaboic's Avatar
Registered User
 
Join Date: Jun 2004
Posts: 1,223
Well, I know this, my 83 300D with 387K and change on the clock always pegs the oil pressure gauge at max on cold start. It usually stays at max during idle until the engine is warmed up, then it drops to about 1.75 to 2 bar at warm idle.

If you are really hung up about the gauge, you could always either swap in another mechanical type gauge as a test, or hook up an oil pressure gauge to the port on the engine and see what is going on.

It is possible that the gauge was sticking internally for some reason and would not go beyond halfway, and when it was removed it was jostled enough to free up the inner workings. A stretch yes, but still possible.
__________________
2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)
Reply With Quote
  #12  
Old 07-06-2022, 10:12 PM
Diesel911's Avatar
Registered User
 
Join Date: Sep 2007
Location: Long Beach,CA
Posts: 51,036
When I bought a new steering Colum lock it came with a new ignition switch. And it needed a new ignition switch as I found the one of the contacts was actually burned off on one side and it was the arm itself conducting the electricity.
__________________
84 300D, 82 Volvo 244Gl Diesel
Reply With Quote
  #13  
Old 07-07-2022, 07:47 PM
Registered User
 
Join Date: Aug 2010
Location: Sacramento, CA
Posts: 3,115
The oil pressure is just a nylon tube to a mechanical (Bourdon tube) gage in the dash. Worst it can do is leak oil. Normal (and good_ to max out after a cold start. Once warmed up and idling, mine read about half-scale and quickly go to max with a little rpm.

Temp gage should read ~82 C once warmed up, whether winter or summer though could creep up slightly under high load on a hot day. A T-stat doesn't regulate to an exact setpoint but rather requires a higher coolant temperature to open more. Engineers term that "proportional droop" in control system theory.

Your engine could actually be overheating and the coolant in the radiator feel cool if the flow is blocked by say a stuck T-stat. But your fuel gage is also reading falsely high, so likely an electrical thing. In 1984 cars, the "boot-up" current for the alternator field generation (google "Motorola alternator", in older GM cars too) is sourced not just from the "BAT warning" lamp, but from several other lamps. Check your wiring diagram. Perhaps if that bulb dies, the current takes another path which messes up the other gage readings. I've never tried that. Anyway, verify that bulb lights when you power up and engine off, then turns off when the engine is running. I know a little of it since I used an LED bulb there which doesn't provide sufficient boot-up current but if I rev the engine slightly the lamp goes out, either from residual magnetism in the alt rotor or current from the other lamps.

__________________
1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans
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 05:14 AM.


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