M177 W205 Upgraded Radiators, Now Transmission Overheats
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GLA45
M177 W205 Upgraded Radiators, Now Transmission Overheats
Last winter I ate a large snow pile with my 2019 C63 S and damaged all the radiators and oil cooler up front. I decided to "upgrade" the radiators with the CSF drop-in replacements thinking better cooling would be better since I have a stage 1 tune on it. Now that the repair is finished, the transmission overheats if I'm getting after it for long enough. This did not happen with the stock radiators at all. It seems to cool fine for normal daily use, but it doesn't take long to get hot when the gas pedal gets some activity. Oil temp and coolant temp seems to run nominal. Coolant level is good, as is oil. I used a vacuum system to fill the coolant, and did a 2nd vacuum pull after about 5 hours drive time just as a double check, even though the coolant level hadn't gone down.
Does anyone have any advice on what I should be double checking to be sure I reassembled everything properly? I assume I missed something. I had the whole front end off the car for this repair. And if anyone can explain how the transmission is actually cooled, that would be great. I called two local shops that I have good experience with and they didn't have any ideas I hadn't tried. Do the two smaller corner radiators have anything to do with the transmission cooling? Could I have forgotten to plug something in there? There is SO much going on in the front of these cars, I could have missed something pretty easily, but I tried really hard not to.
I am looking at getting one of the aftermarket transmission coolers, but I want to make sure it's not something else first.
Thank you for any direction anyone can offer! And ask for any further info I forgot to mention!
Does anyone have any advice on what I should be double checking to be sure I reassembled everything properly? I assume I missed something. I had the whole front end off the car for this repair. And if anyone can explain how the transmission is actually cooled, that would be great. I called two local shops that I have good experience with and they didn't have any ideas I hadn't tried. Do the two smaller corner radiators have anything to do with the transmission cooling? Could I have forgotten to plug something in there? There is SO much going on in the front of these cars, I could have missed something pretty easily, but I tried really hard not to.
I am looking at getting one of the aftermarket transmission coolers, but I want to make sure it's not something else first.
Thank you for any direction anyone can offer! And ask for any further info I forgot to mention!
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⏱️ 700HP Facelift converted C63 S Coupe with Drexler 3.06 plated LSD
Last winter I ate a large snow pile with my 2019 C63 S and damaged all the radiators and oil cooler up front. I decided to "upgrade" the radiators with the CSF drop-in replacements thinking better cooling would be better since I have a stage 1 tune on it. Now that the repair is finished, the transmission overheats if I'm getting after it for long enough. This did not happen with the stock radiators at all. It seems to cool fine for normal daily use, but it doesn't take long to get hot when the gas pedal gets some activity. Oil temp and coolant temp seems to run nominal. Coolant level is good, as is oil. I used a vacuum system to fill the coolant, and did a 2nd vacuum pull after about 5 hours drive time just as a double check, even though the coolant level hadn't gone down.
Does anyone have any advice on what I should be double checking to be sure I reassembled everything properly? I assume I missed something. I had the whole front end off the car for this repair. And if anyone can explain how the transmission is actually cooled, that would be great. I called two local shops that I have good experience with and they didn't have any ideas I hadn't tried. Do the two smaller corner radiators have anything to do with the transmission cooling? Could I have forgotten to plug something in there? There is SO much going on in the front of these cars, I could have missed something pretty easily, but I tried really hard not to.
I am looking at getting one of the aftermarket transmission coolers, but I want to make sure it's not something else first.
Thank you for any direction anyone can offer! And ask for any further info I forgot to mention!
Does anyone have any advice on what I should be double checking to be sure I reassembled everything properly? I assume I missed something. I had the whole front end off the car for this repair. And if anyone can explain how the transmission is actually cooled, that would be great. I called two local shops that I have good experience with and they didn't have any ideas I hadn't tried. Do the two smaller corner radiators have anything to do with the transmission cooling? Could I have forgotten to plug something in there? There is SO much going on in the front of these cars, I could have missed something pretty easily, but I tried really hard not to.
I am looking at getting one of the aftermarket transmission coolers, but I want to make sure it's not something else first.
Thank you for any direction anyone can offer! And ask for any further info I forgot to mention!
Properly installed upgraded coolers will show a massive difference in how the car's cooling works. When I upgraded the coolers on mine it was like night and day. You'll actually struggle to keep temps over 105 degrees C (221f) on a very hot day and giving the car hell and it takes longer for the transmission temps to climb. I'm on Stage 3 with hybrid turbos and the upgraded coolers will immediately shed heat as soon as I coast for a moment. Never had transmission overheat or anywhere near that.
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2017 GLE350 4MATIC
You don’t need new parts.
You need to go back to factory parts or find out why the third party parts you installed aren’t working.
Why are the third party parts not working? Are they the wrong fitment?
You need to go back to factory parts or find out why the third party parts you installed aren’t working.
Why are the third party parts not working? Are they the wrong fitment?
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GLA45
Don't get any aftermarket transmission coolers until you've taken the CSF ones off and made sure there's nothing in them causing a blockage and they are installed properly.
Properly installed upgraded coolers will show a massive difference in how the car's cooling works. When I upgraded the coolers on mine it was like night and day. You'll actually struggle to keep temps over 105 degrees C (221f) on a very hot day and giving the car hell and it takes longer for the transmission temps to climb. I'm on Stage 3 with hybrid turbos and the upgraded coolers will immediately shed heat as soon as I coast for a moment. Never had transmission overheat or anywhere near that.
Properly installed upgraded coolers will show a massive difference in how the car's cooling works. When I upgraded the coolers on mine it was like night and day. You'll actually struggle to keep temps over 105 degrees C (221f) on a very hot day and giving the car hell and it takes longer for the transmission temps to climb. I'm on Stage 3 with hybrid turbos and the upgraded coolers will immediately shed heat as soon as I coast for a moment. Never had transmission overheat or anywhere near that.
Can anyone explain how the transmission cooling circuit functions? That might help me diagnose where the cooling system blockage could be (since there's 4 radiators).
For reference, I'm drifting the car, so it's 2nd and 3rd gear full throttle with 200tw tires. It's definitely doing some work. But it never had an issue with the stock cooling system. So I guess I still assume I did something wrong, I just can't imagine what since it's so straightforward of a swap?
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GLA45
The cooling kit I bought from CSF is a very common kit, and it's a factory fit. The local speed shop here installs them regularly, so they should be good, but like you say, I need to find out what's going on then. I'd like to understand how the transmission cooling system works to help me diagnose the location of the issue. Does anyone know how it works?
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From: unbegrenzt
2017 GLE350 4MATIC
The cooling kit I bought from CSF is a very common kit, and it's a factory fit. The local speed shop here installs them regularly, so they should be good, but like you say, I need to find out what's going on then. I'd like to understand how the transmission cooling system works to help me diagnose the location of the issue. Does anyone know how it works?
- lots of photos of take off radiator and cooling parts
- lots of photos of speed shop radiator and cooling parts
- link to seller of speed shop radiator and cooling parts
- other mods on the car: spoilers, fascia, headlamps, suspension lowered, tire size and offset, intake/induction mods
in other words, the whole story.
Last edited by chassis; Jul 3, 2025 at 10:15 AM.
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⏱️ 700HP Facelift converted C63 S Coupe with Drexler 3.06 plated LSD
Give us the whole story:
- lots of photos of take off radiator and cooling parts
- lots of photos of speed shop radiator and cooling parts
- link to seller of speed shop radiator and cooling parts
- other mods on the car: spoilers, fascia, headlamps, suspension lowered, tire size and offset, intake/induction mods
in other words, the whole story.
- lots of photos of take off radiator and cooling parts
- lots of photos of speed shop radiator and cooling parts
- link to seller of speed shop radiator and cooling parts
- other mods on the car: spoilers, fascia, headlamps, suspension lowered, tire size and offset, intake/induction mods
in other words, the whole story.
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Thread Starter
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GLA45
Give us the whole story:
- lots of photos of take off radiator and cooling parts
- lots of photos of speed shop radiator and cooling parts
- link to seller of speed shop radiator and cooling parts
- other mods on the car: spoilers, fascia, headlamps, suspension lowered, tire size and offset, intake/induction mods
in other words, the whole story.
- lots of photos of take off radiator and cooling parts
- lots of photos of speed shop radiator and cooling parts
- link to seller of speed shop radiator and cooling parts
- other mods on the car: spoilers, fascia, headlamps, suspension lowered, tire size and offset, intake/induction mods
in other words, the whole story.
Here are the products I purchased, I got them Pelican Parts for a better price.
https://csfrace.com/products/8187-me...c63-amg-s-w205
https://csfrace.com/products/8088-me...pr_seq=uniform
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GLA45
In that first photo, you can see the new radiator boxes on the far left, along with the new Mercedes radiator and fan just to the right of that. Other new parts all there too.
The second photo is a bunch of the old stuff being replaced.
The third pic is after most of the damaged parts had been removed to determine what needs to be ordered.
I did document a little bit of it on my Instagram account @richzilla2.0 but not much. Again, more concerned about working on it during my very limited availability to do so, rather than the documentation of it. This has been a 4 month process for me so far.
I appreciate you both being willing to offer any direction. I don't have the kind of money to be bringing this in to have a shop take care of it. It's a stretch just for me to own this thing, ha.
The second photo is a bunch of the old stuff being replaced.
The third pic is after most of the damaged parts had been removed to determine what needs to be ordered.
I did document a little bit of it on my Instagram account @richzilla2.0 but not much. Again, more concerned about working on it during my very limited availability to do so, rather than the documentation of it. This has been a 4 month process for me so far.
I appreciate you both being willing to offer any direction. I don't have the kind of money to be bringing this in to have a shop take care of it. It's a stretch just for me to own this thing, ha.
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GLA45
As far as "the whole story", I was ice racing/drifting with studded tires and when I came around to the same corner I'd been around dozens of times, it now had too much snow on it and the studs had no traction. I slid off the track into the large snow wall and the majority of the front end of the car was pushed in below the bumper.
I had the car hauled to my house and I began disassembling it to repair it myself. As I took it apart, I started ordering parts. The more I dug in, the more I found damaged and the more parts I needed. I just kept ordering parts until I thought I had everything and then reassembled it.
When I did the repairs, everything seemed to go normally. It was a big job and took a lot of time, but nothing seemed out of place or goofy. It all went together pretty smoothly surprisingly enough. I'm wondering if you are correct and one of the coolers was actually blocked inside or something, or if I didn't plug in some pump maybe? The odd thing is that the coolant temp is nominal?
After the repairs. I test drove it for about 3 hours and everything was fine. Then I took it to an invitational drift exhibition at a music festival and started seeing the transmission temps go up over time. At that point I pulled another vacuum on the coolant system to see if more air would come out and it didn't. So then I just did limited runs and kept the temp from getting too high.
Now I'm back home with it trying to determine where to start looking for the issue.
I had the car hauled to my house and I began disassembling it to repair it myself. As I took it apart, I started ordering parts. The more I dug in, the more I found damaged and the more parts I needed. I just kept ordering parts until I thought I had everything and then reassembled it.
When I did the repairs, everything seemed to go normally. It was a big job and took a lot of time, but nothing seemed out of place or goofy. It all went together pretty smoothly surprisingly enough. I'm wondering if you are correct and one of the coolers was actually blocked inside or something, or if I didn't plug in some pump maybe? The odd thing is that the coolant temp is nominal?
After the repairs. I test drove it for about 3 hours and everything was fine. Then I took it to an invitational drift exhibition at a music festival and started seeing the transmission temps go up over time. At that point I pulled another vacuum on the coolant system to see if more air would come out and it didn't. So then I just did limited runs and kept the temp from getting too high.
Now I'm back home with it trying to determine where to start looking for the issue.
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2017 GLE350 4MATIC
Thanks. Lots of repair work was done and potential to have overlooked a needed replacement or a mistake made in doing the work. It happens.
Retrace all of the steps of the work which was done.
After retracing all the steps, take a deeper dive into the transmission cooling circuit.
This car has a small water:oil transmission cooler, correct? Does the transmission have its own cooler at the front, either external or integrated into the engine radiator?
Retrace all of the steps of the work which was done.
After retracing all the steps, take a deeper dive into the transmission cooling circuit.
This car has a small water:oil transmission cooler, correct? Does the transmission have its own cooler at the front, either external or integrated into the engine radiator?
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From: unbegrenzt
2017 GLE350 4MATIC
Did you replace the fascia? Are you 100% certain all airflow is getting into the radiators which should be getting in? Did you change the grille? Is the grille more restrictive than the factory grille? Drifting, etc., is a low speed high rpm high power event, a train wreck from a cooling system point of view. Drifting is a great way to ruin a car imo but that is your choice.
What is the smallest round white orifice (plug?) in the largest radiator in the first photo?
What is the smallest round white orifice (plug?) in the largest radiator in the first photo?
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GLA45
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GLA45
Did you replace the fascia? Are you 100% certain all airflow is getting into the radiators which should be getting in? Did you change the grille? Is the grille more restrictive than the factory grille? Drifting, etc., is a low speed high rpm high power event, a train wreck from a cooling system point of view. Drifting is a great way to ruin a car imo but that is your choice.
What is the smallest round white orifice (plug?) in the largest radiator in the first photo?
What is the smallest round white orifice (plug?) in the largest radiator in the first photo?
I know drifting is a completely ridiculous thing to do with a car like this, but it's the last thing on my bucket list, to see if I'm capable of learning how to drift this specific car in total street setup, no helpers. They have a Drift class at the AMG Academy that uses the C63 and that's how I got the bug up my butt to do it. It is 100% wrong, but also so damn fun it should be illegal. Something about sliding around a huge carousel at 60mph in 3rd gear on the rev limiter makes a guy feel alive.
The white spots on the factory radiator are plugs to keep out debris. I made sure every plug was removed and accounted for during assembly multiple times. Plus, it would not be possible to attach any of the coolant line fittings if the plugs were in place.
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GLA45
Don't get any aftermarket transmission coolers until you've taken the CSF ones off and made sure there's nothing in them causing a blockage and they are installed properly.
Properly installed upgraded coolers will show a massive difference in how the car's cooling works. When I upgraded the coolers on mine it was like night and day. You'll actually struggle to keep temps over 105 degrees C (221f) on a very hot day and giving the car hell and it takes longer for the transmission temps to climb. I'm on Stage 3 with hybrid turbos and the upgraded coolers will immediately shed heat as soon as I coast for a moment. Never had transmission overheat or anywhere near that.
Properly installed upgraded coolers will show a massive difference in how the car's cooling works. When I upgraded the coolers on mine it was like night and day. You'll actually struggle to keep temps over 105 degrees C (221f) on a very hot day and giving the car hell and it takes longer for the transmission temps to climb. I'm on Stage 3 with hybrid turbos and the upgraded coolers will immediately shed heat as soon as I coast for a moment. Never had transmission overheat or anywhere near that.
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GLA45
That's a good point. The repair shop suggested that too, but no lines were ever disconnected for that, so the fluid level should be the same since there have been no leaks or openings. They told me it was difficult to check otherwise I would have checked it just to be sure. I still don't know how to check it, so if it's easy, I would. If someone knows how, let me know.
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'13 s212 63 p30. '06 LX470
That's a good point. The repair shop suggested that too, but no lines were ever disconnected for that, so the fluid level should be the same since there have been no leaks or openings. They told me it was difficult to check otherwise I would have checked it just to be sure. I still don't know how to check it, so if it's easy, I would. If someone knows how, let me know.
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From: unbegrenzt
2017 GLE350 4MATIC
The grill is all the same, just new parts replacing broken parts. The radiators are all very clearly visible and open to airflow. Again, the water temp is right on nominal. No issue with any temps except transmission. That's why I really need to learn how the transmission cooling circuit functions.
I know drifting is a completely ridiculous thing to do with a car like this, but it's the last thing on my bucket list, to see if I'm capable of learning how to drift this specific car in total street setup, no helpers. They have a Drift class at the AMG Academy that uses the C63 and that's how I got the bug up my butt to do it. It is 100% wrong, but also so damn fun it should be illegal. Something about sliding around a huge carousel at 60mph in 3rd gear on the rev limiter makes a guy feel alive.
The white spots on the factory radiator are plugs to keep out debris. I made sure every plug was removed and accounted for during assembly multiple times. Plus, it would not be possible to attach any of the coolant line fittings if the plugs were in place.
I know drifting is a completely ridiculous thing to do with a car like this, but it's the last thing on my bucket list, to see if I'm capable of learning how to drift this specific car in total street setup, no helpers. They have a Drift class at the AMG Academy that uses the C63 and that's how I got the bug up my butt to do it. It is 100% wrong, but also so damn fun it should be illegal. Something about sliding around a huge carousel at 60mph in 3rd gear on the rev limiter makes a guy feel alive.
The white spots on the factory radiator are plugs to keep out debris. I made sure every plug was removed and accounted for during assembly multiple times. Plus, it would not be possible to attach any of the coolant line fittings if the plugs were in place.
What exactly is the smallest outlet on the main engine radiator used for? What is its function?
It is possible your latest round of drifting simply was too much for the transmission cooling system, and your prior sessions didn’t go that far. If you were driving in snow with earlier session, that would make sense, compared to spring or summer (warmer) weather.
Drain the transmission oil. It might be pretty mucky.
Last edited by chassis; Jul 4, 2025 at 08:40 AM.
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GLA45
Yep, I agree, I will be doing that for sure once I get the coolers off and back on again. I'll bring it in for a B service as well.
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GLA45
What exactly is the smallest outlet on the main engine radiator used for? What is its function?
It is possible your latest round of drifting simply was too much for the transmission cooling system, and your prior sessions didn’t go that far. If you were driving in snow with earlier session, that would make sense, compared to spring or summer (warmer) weather.
Drain the transmission oil. It might be pretty mucky.
It is possible your latest round of drifting simply was too much for the transmission cooling system, and your prior sessions didn’t go that far. If you were driving in snow with earlier session, that would make sense, compared to spring or summer (warmer) weather.
Drain the transmission oil. It might be pretty mucky.
The transmission oil check is definitely sounding like a certainty to replace just to be certain.
I still want to learn how the transmission cooling circuit functions. I might be able to call in a favor from a dealer employee who can ask a service pro to talk to me about it. They otherwise aren't too interested in helping you do things yourself.
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⏱️ 700HP Facelift converted C63 S Coupe with Drexler 3.06 plated LSD
I have drifted much harder than I did this session. The air temps were actually cooler than normal this time too.
The transmission oil check is definitely sounding like a certainty to replace just to be certain.
I still want to learn how the transmission cooling circuit functions. I might be able to call in a favor from a dealer employee who can ask a service pro to talk to me about it. They otherwise aren't too interested in helping you do things yourself.
The transmission oil check is definitely sounding like a certainty to replace just to be certain.
I still want to learn how the transmission cooling circuit functions. I might be able to call in a favor from a dealer employee who can ask a service pro to talk to me about it. They otherwise aren't too interested in helping you do things yourself.
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GLA45
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2015 C400 4MATIC Palladium Silver Metallic
The M177 and 9g-tronic cooling system on the C63 is very similar to the cooling system on the C43 (and C450/C400) it just has a couple of extra rads and pumps.
There's a "High temp cooling circuit" this is for the engine and the engine and engine oil only. It flows through the main radiator, the engine's coolant passages, and through the engine oil cooler/filter assembly.
The "low temp cooling circuit" cools the air to water intercoolers (turbo outlet charge coolers), and the transmission.
The transmission fluid is pumped up to an fluid interchange cooler where hot trans fluid and the "low temp circuit" coolant pass though a series of sandwiched plates and the heat from the warmer fluid is absorbed by the cooler fluid. Typically the trans is warmer (after the thermostat in the interchange cooler allows full flow).
On the M276.8 engine these two circuits are completely separate. I believe it is the same on the W205 M177.
Things to check on your low temp circuit:
1) electric pumps this is the number one failure mode.
2) leaks at the trans cooler heat exchanger
3) correct operation of trans cooler heat exchanger thermostat
4) proper trans fluid level
5) unobstructed trans cooler lines
Last edited by TwoC400s; Jul 5, 2025 at 09:16 PM.
