Thank you Mxfrank! That is correct.

In searching net, I have found several posts where owners have had same problem. Dealer even sells the nut and a seal washer. I will order these Monday. Just hope the flare nut comes apart easily. May have to protect threaded nozzle and hold with vicegrips.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

I do not think that either.... as it would be in hot engine coolant instead of being ' exposed' to air for cooling...

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

That's exactly how transmission coolers work. There's a water-to-oil cooler located in the cool side tank of the radiator, and plumbed through the side of the tank. There are air-to-oil coolers which are separate from the radiator, but not on most benz's.

It seems that is the way it is. Probably helps warm up transmission oil on start up and keeps it at coolant temperature when running.

To keep thing here, check out Fig 9 in this Peachpart link. It shows the Transmission Cooler connections at base of radiator.

http://www.pelicanparts.com/techarticles/Mercedes-W126/13-WATER-Radiator_Replacement/images_med/pic09.jpg

What the heck - here is the pic You can see the coolant drain right under the driver side nozzle.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

The transmission oil heat exchanger should be all brass. The broken nut just holds and seals the heat exchanger to the radiator tank. Undo the flare nut then get another nut to replace the broken one (you may have to custom make one).

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

This is the standard way to implement a transmission cooler. You'll find the same arrangement in just about any car that's every been equipped with an automatic. The tranny cooler is on the cool side of the tank, so you have a 10-20 degree drop from engine operating temperature. That's a very comfortable temperature for the transmission.

Attached Thumbnails

 

Fair enough - nice one

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

No one else, is concerned...That if that nut was brittle enough to fail, that the rest of the plastic radiator isn't just as brittle?

No one else is worried, that the bottom of the radiator, is where all the gunk falls too? That green coolant is the wrong coolant to use in a plastic/aluminum radiator? As well as it becoming to acidic with age?

Hmmm.....My personal feelings, I know get tramped....Would tell me just replace the radiator.....Fill with proper coolant and won't need to worry about future fractures in the plastic for another 30 years...regular coolant changes included....

Turbo radiators, are climbing steady....Soon they will be just like the NA radiators....NLA....and the few left close to 800$...

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I see a simple improvised fix. Instead of making a custom nut, forego it and get a tight fitting nitrile washer and a bunch of spacers and use the flare nut as the nut to secure and seal the heat exchanger. I think that style of heat exchanger is called tube in shell.

Edit: Forget it, not a good idea. Don't want the flare nut to come loose which is a possibility with expansion contraction

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I am going to order the nut and seal washer from the dealer. Probably do the other side too if it looks bad. Hopefully the flare nuts will come off without needing too much force. Otherwise I will have to grip the nozzles.

Don't know what the nuts are made of, but it isn't plastic. More likely they are brass when they should probably be bronze. I have now read of several similar nuts that have failed. Probably why MB stock them as a part. If a new one will last another 30 years, it will definitely outlast me

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

The nipples should be brass and I believe silver soldered to a brass tube and plenty strong to torque on to get the flare nut off. Use penetrating fluid to help it. Great that it is available from the dealer. I am surprised the nut is round. What tool are you suppose to use to tighten it? A chisel?

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Automatic Transmission Fluid | What You Need to Know.

Automatic Transmission Service | Wayne's Transmissions

having the trans fluid mechanically and therefor thermally restricted by being inside the radiator may account for the relatively short change out schedule recommended by MB...

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/showthread.php?threadid=10414

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

It is hex on the other side! My picture was of the side that faces the tank. You can see the hex head in the pics above (red arrows)

If need be, I might use a small butane torch or hot air gun on the flare nut. Just getting it up to 100C or so should help. Did that when taking brake lines apart. We will see how it goes. Don't want to torque the cooler nozzles' internal joint if I can help it.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Use a flare nut wrench and give it a sharp impact it with your palm.

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

A torch is a bad idea, because the tanks are plastic and the hose is rubber. If the nut won't turn, use a dremel to carefully split it and peel it off the fitting.