M-Class (W164) Produced 2006-2011: ML280CDI, ML320CDI, ML420CDI, ML350, ML500, ML550

Help Needed - Transmission Cooler Radiator Fittings

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Old Sep 22, 2017 | 11:56 AM
  #1  
-AJC-'s Avatar
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2006 ML 320 CDI
Help Needed - Transmission Cooler Radiator Fittings

Hopefully someone can help on an issue with the transmission cooler radiator fittings?

I'm referring to the upper and lower transmission hoses that are connected to the right hand side of the radiator.

I have a major leak from the upper fitting from the union that is fitted to the radiator. The leak is not from the thread but from around the female fitting that sits flush with the outer casing of the radiator. When I screw the male fitting back in place just gentle pressure on the thread causes transmission fluid to gush out around the outer edge of the female end that sits flush with the radiator. Currently the only seal to prevent fluid loss is the metal washer fitted to the male fitting.

A few images to explain what I mean.......

Upper and Lower Transmission Cooler Lines



Upper Transmission Cooler Line - 19mm nut and washer



Female connection on the radiator



Transmission fluid leaks from around this edge






So with the male fitting attached and the pipe connected, just pushing on the fitting will cause transmission fluid to leak. I have tightened the 19mm nut as tight as I dare but still have transmission fluid leaking from behind the washer.

Should tightening the male fitting cause the female end to sit tight with the edge of the radiator and create an air tight seal? Or should the female end already have an airtight seal and so my radiator needs replacing?

Would appreciate some advice from anyone with first hand experience before I spend a further £450 with the main dealer?
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Old Sep 22, 2017 | 01:20 PM
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Maj. Dundee's Avatar
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Could these parts be your problem?
Attached Thumbnails Help Needed - Transmission Cooler Radiator Fittings-2017-09-22_131820.jpg  
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Old Sep 22, 2017 | 01:30 PM
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No the leak is from the female end on the radiator.
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Old Sep 22, 2017 | 04:50 PM
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Originally Posted by -AJC-
No the leak is from the female end on the radiator.
Then that is part of the radiator which is installed by the manufacturer.
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Old Sep 25, 2017 | 09:06 AM
  #5  
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Had it confirmed that the male connectors for the transmission cooler are fitted at the factory and should not be removed, otherwise the o-ring seal will be impaired.

This is indeed time for a new radiator.
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Old Sep 25, 2017 | 09:39 AM
  #6  
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Originally Posted by -AJC-
Had it confirmed that the male connectors for the transmission cooler are fitted at the factory and should not be removed, otherwise the o-ring seal will be impaired.

This is indeed time for a new radiator.
Buy a quality part, you don't want to do this twice.

Here are the directions.
Attached Files
File Type: pdf
R&I Radiator 642 Eng.pdf (132.3 KB, 992 views)
File Type: pdf
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Old Jan 5, 2019 | 09:43 PM
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Can someone confirm the oil flow for me please? Does it go to the cooler with the fan attached first, then the small cooler on the bottom of the heat exchanger, or does it flow to the small one on the bottom of the heat exchanger first then to the cooler with the fan attached?

thank you.
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Old Jan 7, 2019 | 01:58 AM
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All radiator oil cooling flow goes into the top line and returned by way of the lower line.

Why the question about the cooling fan?
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Old Jan 8, 2019 | 08:31 AM
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Originally Posted by Maj. Dundee
All radiator oil cooling flow goes into the top line and returned by way of the lower line.

Why the question about the cooling fan?
Ok, so through the small radiator first then right? need to move it because a much larger heat exchanger is causing it to droop down below the bumper, thanks
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Old Jan 8, 2019 | 08:57 AM
  #10  
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What vehicle are we referring to? Be specific.

And what oil, trans. or PS?

Last edited by Maj. Dundee; Jan 8, 2019 at 09:17 AM.
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Old Aug 11, 2020 | 03:45 PM
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both pipes have a joint nearer the radiator

Originally Posted by -AJC-
Hopefully someone can help on an issue with the transmission cooler radiator fittings?

I'm referring to the upper and lower transmission hoses that are connected to the right hand side of the radiator.

I have a major leak from the upper fitting from the union that is fitted to the radiator. The leak is not from the thread but from around the female fitting that sits flush with the outer casing of the radiator. When I screw the male fitting back in place just gentle pressure on the thread causes transmission fluid to gush out around the outer edge of the female end that sits flush with the radiator. Currently the only seal to prevent fluid loss is the metal washer fitted to the male fitting.

A few images to explain what I mean.......

Upper and Lower Transmission Cooler Lines



Upper Transmission Cooler Line - 19mm nut and washer



Female connection on the radiator



Transmission fluid leaks from around this edge






So with the male fitting attached and the pipe connected, just pushing on the fitting will cause transmission fluid to leak. I have tightened the 19mm nut as tight as I dare but still have transmission fluid leaking from behind the washer.

Should tightening the male fitting cause the female end to sit tight with the edge of the radiator and create an air tight seal? Or should the female end already have an airtight seal and so my radiator needs replacing?

Would appreciate some advice from anyone with first hand experience before I spend a further £450 with the main dealer?
Both pipes have a joint nearer the radiator,Usually these pipes are replaced as the joint usually has an internal split that cannot be repaired.parts around 60 quid for a pair.just replace them instead of the gearbox end.
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Old Dec 10, 2022 | 08:36 AM
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2008 ML320 CDI
Originally Posted by Maj. Dundee
All radiator oil cooling flow goes into the top line and returned by way of the lower line.
I'm going to have to do this same job and I had a question about this: I expect that when I disconnect the transmission lines, transmission fluid is going to leak out. I was hoping to prevent that, since I don't really have a good way to replenish it at home. Would I be able to purge the radiator with something like compressed air, to get most of the fluid back into the transmission, before I disconnect the bottom line? I suppose I could take it to a shop once the new radiator is in but I have no idea how much trans fluid I'm going to lose, and my local dealer is refusing to work on my vehicle because its too old.

Thanks in advance!
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Old Jun 10, 2025 | 11:31 AM
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I just replaced the radiator, the transmission cooler has about 8oz - 10oz of fluid inside.
Once the new radiator is in place and lower cooler line is connected, refill the transmission fluid from top hole before connecting the top line.

A better and more accurate way of filling/checking transmission fluid is to open the transmission drain plug once ATF is reached 45C, to let excessive fluid out or fill if nothing come out.

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