Well, here I go again...

I've replaced almost every component in my cooling system (1983 300cd T) with new, good parts and am still experiencing temps around 90C and sometimes even 100C in the past few days. All the following have been replaced:
-Temp Sensor $20
-Temp Gauge (incidental, not as a fix) $20
-Radiator $200
-One thermostat was bad, the one in now is good. $40
-Expansion Tank Cap $7
-Water Pump $80
-Fan clutch $50

Over the last few months I've been using a hollow thermostat body to hold the seal in place with the mechanism drilled out. This worked and kept the temperatures at 65 city and 80-85 highway. A few days ago I put in a new thermo since I found out the system is designed such that the thermo is not just a straightforward open or closed deal.

So now I put in this new thermo, which I know is right on the money, and my temperatures rise again to around 90C and up to 100C. I don't think that my cylinder head could be cracked because the car runs great and I'm not losing coolant. I don't think that my water pump/fan belt being a little too tight or loose could produce this pronounced an effect. There's no way any of the parts above are bad.

I did read in the 123 engine manual that there is an arrow on the thermostat and it should be pointing up...I didn't do this, could this be my problem? It doesn't seem to be an air bubble because I can't feel any in the upper hose.

__________________
"I would rather be ashes than dust!
I would rather that my spark should burn out in a brillaint blaze
than it should be stifled by dryrot.
I would rather be a superb meteor,
every atom of me in magnificent glow,
than a sleepy and permanent planet.
The proper function of man is to live, not to exist.
I shall not waste my days in trying to prolong them.
I shall use my time."

-Jack London 1876-1916

1983 300CDT (running WVO since 12/05)
1981 300SD (parts car)

Is this a turbocharged engine? I'm just asking because my n/a motor runs at about the same temp. Sometimes even a little hotter. I've read many threads which say the normal operating temp ranges from 80-120C, and as long as the car isn't puking coolant, that it isn't a source of concern. I think I'm going to retrofit mine with a turbo radiator, just to see what kind of difference that makes. Wish I could be of more help, but I think this is just the way things are for the non-turbo cars. If you find a solution, and have a little extra time, email me to let me know how you got it running cooler.

Thanks,
Jay.

According to everything I have read on this topic (especially service bulletins from Mercedes) temps of 90 to 100 are not overheating. Particularly in high outside temp with ac under load. I think you are obsessing about this problem, maybe.

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1984 300SD 326,997 miles and counting . . . No wait, my odometer is still dead

Running between 90 and 100 is pretty normal. I know that after I replaced most of my cooling system (radiator, thermo, water pump), it still runs between 90 and 100, but I also know that my temp gauge reads about 13 degrees celsius too high. Took it to the firehouse my dad works at and used an IR heat gun and was getting temp readings of around 185*F (85* C) when the gauge was reading about 98. You might want to look into trying to find someone with a heat gun to get more accurate readings.

I agree. I was actually reading up on this today becasue at idle my car gets near 120 .. which i think is due to the aux fan not kicking in.. but 90, from what everyone says, is perfectly ok.

I do have a question though.. not to hijack this.. but does the engine fan always run or is it only supposed to engage at a higher temp?

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'87 300D new to me
'85 300D Sold
'83 300cd Sold

Are you assuming that the 20yo temp system is still OK? This issue keeps coming up and coming up and coming up. Go get yourself a digital laser thermometer (or borrow one from your mechanic). Aim it at the base of the temp sender and compare that to the reading at your gauge.

The following is from my engineer/geek buddy who works on satellites at Boeing (formally Hughes). The temperature of the wire between the gauge and the sending unit will change the resistance of the wire.

Back in the archives there is a table of resistance/readings from a gauge. A 1 ohm change in resistance will change the gauge reading fairly significantly (5 degrees? I don't exactly remember). So you can see if the wiring in the temp reading system changes in temperature, the resistance changes and the gauge will not read accurately.

I don't think your gauge is that far off and the 5 or 10 degree difference between different cars seems reasonable to me. Until you develop a base of comparison, you can't really judge whether your system is reading accurately or not.

I know its unnerving to read a high temp gauge, but maybe it isn't high to start with...........

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84 300DT Puke Yellow. Totalled after 438,000
84 300DT Orient Red. 169,000 (actual mileage may vary)
2002 Explorer EB (wife's)

The engine fan is engaged based on ambient air temperature around a metallic strip on the fan clutch. This metal stip changes shape and allows a valve to open which causes oil in the fan clutch to engage it at higher temperatures. When the temperature is lower, however, the fan clutch causes the fan to freewheel, adding engine power and fuel economy.

As far as your high temp being caused by the auxiliary fan...the auxiliary fan is engaged based on coolant temperature inside the AC condensor rather than engine coolant temperatures. Each is part of a seperate cooling system. While an overheating condensor might cause your radiator to heat slightly due to its proximity, it would not cause as significant a shift in temperature as you mentioned.

As far as I know, it is not really acceptable to have this vehicle (1983 300cdt) running at a temperature consistently above 90C and I really don't think my gauge is showing the wrong temperature because I just put in a new sensor and gauge. I hope I'm not obsessing about this, I just don't want to cause excessive engine wear due to high heat and thermally broken down oil in the only car I own.

__________________
"I would rather be ashes than dust!
I would rather that my spark should burn out in a brillaint blaze
than it should be stifled by dryrot.
I would rather be a superb meteor,
every atom of me in magnificent glow,
than a sleepy and permanent planet.
The proper function of man is to live, not to exist.
I shall not waste my days in trying to prolong them.
I shall use my time."

-Jack London 1876-1916

1983 300CDT (running WVO since 12/05)
1981 300SD (parts car)

The guage on your dash is 20 years old so it is only aprox. 80c-90c is perfectly normal. With the AC on 100c is normal as well, more so if the engine is under load like on the highway or sitting in traffic. I would say anything 110C+ is not normal, but according to MB as long as the guage is out of the red you are fine.

Running a diesel to cold is worst then running it hot. 65c is to cold you really do not want your engine to run below 80C.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200

it was a very interesting read...

anyway, what about the oil cooler thermostat? heres the method to check its function...

http://rbk3.com/mbz/tsm/MBZ18-120%20OIL%20THERMO.pdf




ps. I cannot understand why yours ran cooler w/ the hollow body thermostat. theories?

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Cheers,
Robert

The t stat is a bi metal that expand and contracts based on the coolants temp. If you by pass it the coolant will flow all of the time resulting in lower engine temps. I was just looking at my service CD and according to MB the thermostat on a 617 does not start to open until 80C. At 94C the t stat should be flowing fully. Also according to them removing it to get lower temps is a mistake, another thing seems to by pass it at 94c as well.

So basicaly according to MB the cooling system is not flowing fully until 94C.


83mercedes send me your email I will shoot you the pdf if you don't have it already.

__________________
2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Actually, I just got the Benz shop manuals on CD today from someone who copied them for me and did the same research as you guys. I had no idea about the thermostat not being at full open till 94C!!!

Wow, that would have saved me a lot of money .....but I suppose the up side is I have new components in my cooling system that I won't have to replace (fingers crossed) for another decade or two.

On my previous cooling problem posts no-one gave me any indication of this.....

those manuals on CD sure are handy, they've got so much more info than the Haynes, and allow you to actually conceptualize the workings of the parts rather than just how to switch them out.

well, I'll probably keep tinkering and try to get the temp. lower, but that's good to know I'm not going to ruin my engine.

Does anyone know if it matters if the thermostat arrow is pointing up? It doesn't seem like it should, since the design is symmetrical so far as I can tell.

__________________
"I would rather be ashes than dust!
I would rather that my spark should burn out in a brillaint blaze
than it should be stifled by dryrot.
I would rather be a superb meteor,
every atom of me in magnificent glow,
than a sleepy and permanent planet.
The proper function of man is to live, not to exist.
I shall not waste my days in trying to prolong them.
I shall use my time."

-Jack London 1876-1916

1983 300CDT (running WVO since 12/05)
1981 300SD (parts car)

no the aux fan should kick in at a bit over 100 deg C ..whether the a/c is on or not.. at least it does with my car. your idle temp is way too high..
you need to diagnose your system.
it could be your t-stat or radiator. are they original?

FWIW i have the original radiator still in my car and temps in summer run between the 80 and 100 deg C mark consistantly. as said the aux fan kicks on above 100C and brings the temp down quick.

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1984 300D Turbo - 231k....totalled 11/30/07 RIP

Hey 83Mercedes, I was having the same worries, only I at first did have a wter pump going out and a bad thermo, and then found tht the radiator was leaking. After $400 and repairing and replacing all of those items I was and am still at 90-100 sometimes a little over 100 if in traffic with the A/C cranked up high (coming out the side vents only thanks only to my tolltag wedged under the arm of the actuator in the glovebox .....NEXT PROJECT...hehe) I have come to the conclusion after reading on and on that I just need to get over it and if it ain't in the red just keep movin'! After always used to have driven Caddys and Lincolns I guess the temp guage just kinda jumped out at me in the Benz when I know that 100c is at boiling.

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-Chris
'89 300E

yes it matters. there is an up and a down. if you put it in upside down it will not function properly at all. it will overheat, if my mimory serves me correctly.

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[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.

God$%#(UI(@ I'm so sick of taking thermostats in and out!!!! I've used SOO much time and coolant doing all these cooling system projects I'm ready to just leave it alone for 2 years like the manual says you do (wishful thinking, I suppose) until the next flush.

It's funny the Haynes manual doesn't say anything about this, and too bad I got the Mercedes manual CD after the fact.

Oh well, if this makes my temps drop, I'll report back.

__________________
"I would rather be ashes than dust!
I would rather that my spark should burn out in a brillaint blaze
than it should be stifled by dryrot.
I would rather be a superb meteor,
every atom of me in magnificent glow,
than a sleepy and permanent planet.
The proper function of man is to live, not to exist.
I shall not waste my days in trying to prolong them.
I shall use my time."

-Jack London 1876-1916

1983 300CDT (running WVO since 12/05)
1981 300SD (parts car)