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#1
09-12-2012, 08:43 PM
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87 300D temp peggs on gauge.
I have changed the sender, with O.E. from the dealership. and my IR gun reads 188 after a long drive, and the radiator is still 1/2 cool. new thermostat, and fan clutch and 602 plastic fan blade... WTF?
are cluster gauges likely to cause issues?
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread "as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do! My drivers: 1987 190D 2.5Turbo 1987 190D 2.5Turbo 1987 190D 2.5-5SPEED!!!  1987 300TD 1987 300TD 1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere! 
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#2
09-12-2012, 09:40 PM
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If I recall, a high-resistance or "open" sender keeps the needle on low, while a lower-resistance cause the needle to travel up. So, a really low resistance (bad unit) or a short circuit (grounded sender wire) might explain the needle pegging high.
Disconnect the sender and measure the Ohms of the sender to ground. OK, how about volts from the sender wire to ground? I may be confusing the M-B with old Mopars that used a funky 5V regulator for gauges, but the Mopar regulator would sometimes stick and put 12V on the gauge lines, and boy, would they peg!  If the M-B uses a similar system, you should not measure more than 5V on the wire with the sender unplugged.
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#3
09-12-2012, 09:44 PM
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Sounds like you have gotten the sender grounded. What ohm reading are you getting from the sender to ground ?
__________________
1985 300D 198K sold 1982 300D 202K 1989 300E 125K 1992 940T "If you dont have time to do it safely, you dont have time to do it" "The democracy will cease to exist when you take away from those who are willing to work and give to those who would not."
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#4
09-12-2012, 10:00 PM
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I'll check.
it's REALLY tight in there... with the sender unplugged, the gauge does not register any temp. connected to a brand new sender, it seems to register temp, as cold it registers cold, but the temp quickly climbs to 60/80/100, at idle, then as soon as the car hits the road, it clears 100, and begins to peg to top scale... my IR gun no matter WHERE i aim it on the head, never exceeds 188. most of the head is around 150... I put a good water pump in, the thermostat is new and good... odd that it's down in the block, not in the head. perhaps the block has some corrosion in it. the waterpump was very corroded. very little heat gets into the radiator (also brand new bher unit...)
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread "as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do! My drivers: 1987 190D 2.5Turbo 1987 190D 2.5Turbo 1987 190D 2.5-5SPEED!!! 1987 300TD 1987 300TD 1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
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#5
09-12-2012, 11:07 PM
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188F is about 86C so you are definitely not overheating, it's a gauge problem.
It seems like maybe you got a bad sensor or they cross referenced you the wrong one. Maybe they mixed up the glow plug sensor, aren't they the same mounting and in close proximity on the engine? Also remember the radiator is sized for worst case scenario to always be able to shed more heat than the engine can produce. Otherwise you would have a thermal runaway condition in the engine. GP sensor probably has a different curve than the gauge sensor.
__________________
The OM 642/722.9 powered family Still going strong 2014 ML350 Bluetec (wife's DD) 2013 E350 Bluetec (my DD) both my kids cars went to junkyard in 2023 2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles) 2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles) 1998 E300DT sold to TimFreeh 1987 300TD sold to vstech
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#6
09-12-2012, 11:07 PM
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Sounds like a bad gauge or possibly a bad ground in the instrument cluster. I haven't done any experiments to see what happens if the ground at the gauge is disconnected.
Jeremy
__________________
 "Buster" in the '95 Our all-Diesel family 1996 E300D (W210) . .338,000 miles Wife's car 2005 E320 CDI . . 113,000 miles My car Santa Rosa population 176,762 (2022) Total. . . . . . . . . . . . 627,762 "Oh lord won't you buy me a Mercedes Benz." -- Janis Joplin, October 1, 1970 Last edited by Jeremy5848; 09-13-2012 at 12:48 AM. Reason: typo
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#7
09-12-2012, 11:13 PM
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X2, that was going to be my next suggestion too. I suspect the gauge is a "bridge" measuring circuit and so would rely on the ground at the cluster to perform correctly.
__________________
The OM 642/722.9 powered family Still going strong 2014 ML350 Bluetec (wife's DD) 2013 E350 Bluetec (my DD) both my kids cars went to junkyard in 2023 2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles) 2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles) 1998 E300DT sold to TimFreeh 1987 300TD sold to vstech
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#8
09-13-2012, 02:49 AM
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Over voltage protection relay?
The 124's have electronics in the temp gauge wiring. I have the same issue with mine. Have just learned to live with it for now. I am going to put the temp gauge & sender out of my old 123 D in it one day. The old electric, not electronic gauges are far more reliable. Good luck John, if you find an easy fix please let us know.
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Grumpy Old Diesel Owners Club group I no longer question authority, I annoy authority. More effect, less effort.... 1967 230-6 auto parts car. rust bucket. 1980 300D now parts car 800k miles 1984 300D 500k miles  1987 250td 160k miles English import  2001 jeep turbo diesel 130k miles  1998 jeep tdi ~ followed me home. Needs a turbo. 1968 Ford F750 truck. 6-354 diesel conversion. Other toys ~J.D.,Cat & GM ~ mainly earth moving
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#9
09-13-2012, 10:59 AM
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I had a very similar experience after replacing the sender with an OEM unit from the dealer. I asked the question of an indie when I took the car in for something I couldn't handle. Turned out the sending unit I was given at the dealer ($$$) was the wrong one. The unit was replaced and all was well.
Double check the sending unit. They are NOT all the same.
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#10
09-13-2012, 01:11 PM
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at the dealer, I looked it up by VIN, and it is the sender in the head for the temp gauge...
next step is to pull the cluster back out, and make sure of the grounds...
__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread "as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do! My drivers: 1987 190D 2.5Turbo 1987 190D 2.5Turbo 1987 190D 2.5-5SPEED!!! 1987 300TD 1987 300TD 1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
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#11
09-13-2012, 02:36 PM
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Ground straps for the engine? (WAG)
__________________
http://superturbodiesel.com/images/sig.04.10.jpg 1995 E420 Schwarz 1995 E300 Weiss #1987 300D Sturmmachine #1991 300D Nearly Perfect #1994 E320 Cabriolet #1995 E320 Touring #1985 300D Sedan OBK #42
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#12
09-13-2012, 04:23 PM
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Quote:
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#13
09-13-2012, 05:21 PM
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ya wouldn't happen to have a part number would ya?
__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread "as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do! My drivers: 1987 190D 2.5Turbo 1987 190D 2.5Turbo 1987 190D 2.5-5SPEED!!! 1987 300TD 1987 300TD 1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
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