I took my 82, W123 300D in to my local MB garage as it gets to 100 - 105 with no problem. Yes, it's hot out -appx 95f. And yes, I had my A/C on. But talking to my mechanics, it should not get that hot. They suggested that for a 25 year old car, I should replace the radiator and t-stat. I had them do the water pump at the same time. After all repairs, it still stays in the same temp range. Can anyone assist? What am I missing?
Will submit all answers to my MB mechanic. Thank you!

Might look into you auxillary water pump.

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1984 300d Turbo 144,000
Replace The Fan Clutch,$168.00 Diy 1 Hr, 4 10mm Bolts, 4 13mm Bolts Temp Now 80 C, Take Upper Radiator Hose At Top Of Radiator And Fill With Water, You May Have Air In Top Of Engine.

I thought om617 didn't have a fan clutch, at least my om616 didn't.

Try to remove the water radiator and clean it thoroughly. Then clean the a/c radiator as well without removing it so you don't loose a/c gas. Clean them from outside as overtime a lot of junk gets between the radiators.

A buddy of mine has a w124 200ce (gasser coupe) and whenever he was using the a/c the car was overheating. Cleaned the radiator and the car works flawlessly now. There was a lot of junk between the radiators.

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1992 Mercedes 190D 2.5 turbo 5sp manual. EGT+boost gauges. Boost controller set to ~14.5 psi. 1 1/4 turns on full load adjustment. LPG injection. Next in the list is water injection.

Yes, the 617 uses a fan clutch. Also replace the temperature sensor on the cylinder head.

As Lance (FI) mentioned, first verify that the temp on the dash gauge is correct. You can either do this by measuring the coolant temperature independently (best way), or just go ahead and replace the temp sensor (less than $20, very easy).

If it is reading a true temp then you can proceed to troubleshoot the system.

The sensor is very cheap and you don't have to drain the coolant to change it. Mine was constantly reading low. It would always display 60*c at operating temperature. Replacing it brought the display back to showing 82*c like it should.

The sensor goes through thousands of thermal stress cycles of going from ambient to 180-212*f and back. Sometimes they will increase their resistance and sometimes they will loose their resistance.

test different areas with a laser temp gun or continue to throw money at it- either way keep smiling

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Brian

82 300d turbo 164k - passed on
83 sd - passed on
04 civic hybrid - DD
06 GTO for sale - passed on
84 VW Rabbit Diesel 4dr.- passed on
94 S350D - DD
94 S320 - soon to be DD

+1 for changing the temp sender to verify it is actually running at the temp the guage reports.

Also, is the aux fan (the electric fan in front of the radiator) coming on?
I would think this would be the first thing the mechanic would check.

Fan clutch... maybe.

Might try some "water wetter" .

http://www.redlineoil.com/products_coolant.asp

I have to ask. When referring to the fan clutch what exactly do you mean? If talking about the engine fan is that not directly driven by the fan belt like on a 240D?

- Peter.

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2021 Chevrolet Spark
Formerly...
2000 GMC Sonoma
1981 240D 4spd stick. 347000 miles. Deceased Feb 14 2021
2002 Kia Rio. Worst crap on four wheels
1981 240D 4spd stick. 389000 miles.
1984 123 200
1979 116 280S
1972 Cadillac Sedan DeVille
1971 108 280S

Correct, unlike the 240D, the 300D has a thermostatic clutch that drives the mechanical fan. It looks like this:

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1CQ0J3JZ425M188UCG&year=1982&make=MB&model=300-DT-001&category=All&part=Fan+Clutch&appEngines=_any

I see. That seems the height of stupidity to me. Pity you can't reverse engineer the car to take the 240D's directly driven fan.

The symptom of getting up to 105 or 110 very quickly and then staying there makes me think of a possibly inaccurate temperature sensor. I'd second the motion of independently verifying the temperature before proceeding.

- Peter.

__________________
2021 Chevrolet Spark
Formerly...
2000 GMC Sonoma
1981 240D 4spd stick. 347000 miles. Deceased Feb 14 2021
2002 Kia Rio. Worst crap on four wheels
1981 240D 4spd stick. 389000 miles.
1984 123 200
1979 116 280S
1972 Cadillac Sedan DeVille
1971 108 280S

You probably could if you wanted to, the clutch fan does reduce the power consumption and noise a little. The only problem with the clutch is that it's a little expensive to replace. A bad clutch will usually result in the car heating up in traffic, but it shouldn't cause overheating at highway speeds.