Gents,

My engine has stand alone tranny oil cooler.
However, my friend's W204 C200 with M271 EVO or W212 E200/250 in some countries....is still using combined radiator and tranny oil cooler.

I was trying to find out how actually the tranny oil cooler is installed on the radiator and how people are failing their transmission from coolant mixing with their tranny oil.
The famous milkshake coolant + tranny oil mix.

It seems the weakness is not the tranny metal cooling plate corroding ( well maintained car ) , it is AGAIN the freaking seal or flat o-ring....DUGHHH !!!!


Typical tranny oil cooler cooling plate , inside a combo radiator.


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Item 2 in red is the flat seal.




So, if flat seal #2 failed and also o-ring #1 at the fitting has gone bad, coolant in tranny oil mix will happen.
while one can replace #1 o-ring assuming you can find the same one in open market, the #2 flat seal is not accessible unless you tear down the radiator.




The youtube channel of the images.





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Same overall fitting and sealing style for Mercedes. Older W211 E240.




I told my friend to buy a new radiator, for the sake this milkshake prevention and tranny total loss if not total overhaul. His car is 14 years old today, 93,000KM.
US$500 ish in Indonesia from MB dealer for his radiator....ouch !!!!

So, you owners of combo radiator with oil cooler, now you know the failure mode.
There is nothing one can do to prevent or to predict....Damn !!!!

 

I'd just bypass the rad and install an aux cooler. Once I had no cooler in my truck, just a line out, u-turn, back in. It did not have a lockup converter, in fact it was a 2400 stall, so it generates a lot more heat, yet it was fine. I would never tow like that, but it was fine for normal driving. I forget why I had it like that, but it was a temporary thing. An oem lockup converter would make far less heat, but obviously an aux cooler is the way to go.
When I was kid I had a car that used the radiator, and the trans was xx temp over the eng temp. I think 20F but it's been a long time. I put a generic aux cooler on after the rad, barely helped. Then bypassed the rad and trans hovered ~160F.
Later, in my truck, I switched to a 3200 stall converter, and while off road in the sand/racing etc in desert heat, even a regular trans cooler wasn't cutting it. So I made one from the A/C condenser of a some small car at the junkyard, mounted it under the bed with a fan and it worked awesome.
So imo the radiator cooler is not a cooler, but a trans heater. And of course a timer to destroy your trans when it leaks.

 

This friend of mine, I rather keep his car standard as is.

To think about it, even say per 12 years he need to speed US$800 for the radiator + tranny oil cooler combo installed, that is still cheap, US$67 per year only.
A2045002203 Water Cooler ( radiator engine + tranny )

In the USA it is much cheaper, US$124 only , after discount before sales tax & installation labor not included.

 

well that is scary. I think mine still plugged to the radiator. Any guide what size of connectors and hose to use to bypassing the stock cooler? I'm going to install external atf cooler.

 

If indeed your tranny oil cooler is combo to the radiator.........

01. I do not recommend modifying it to make it a stand alone tranny oil cooler.
My friend's C204 C200 M271.8 EVO engine its combo radiator is Rp9.5 mil ( US$625 ) at Dipo Pluit, most likely an M272.9 combo radiator would probably be very similar in price or 2.5x of USA dealer.
Keep it original, safer and proven this 14 years its been good.

02. If you go for original, you then get new radiator too, which its plastic sides will one day leak and crack.....anyway.

03. You can also go for branded aftermarket one like BEHR or VALEO, if it is 100% the same. These 2 brands are OE for the Mercedes.
Example my friend's C200 radiator is by Valeo



If the Valeo direct, I think Rp4 mil max.
Too bad I do not know the actual Valeo P/N, as sometimes it could be MB specific order to Valeo and Valeo then issue MB P/N as per MB instruction , while hiding their own original P/N.


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Your W212.054 E300.
+427 positive sign means it is FOR 427 code, which means 7 speed auto. So yours is a combo radiator with tranny cooler too. Best check the 2 small 2cm ish diameter tranny oil ports at the radiator side.
-917 minus sign, means it is NOT for 917 code.





US$257 in USA, genuine
https://www.mbpartsexpress.com/oem-p...tor-2045004303


US$331 in FCP Euro for genuine. Ignore the cheaper Nissen brand. I read it is not that good nowadays...so I read.
https://www.fcpeuro.com/Parts/?keywords=2045004303

 

@S-Prihadi so its not recommended to bypass the stock cooler? My other car (a kijang) got external atf cooler installed (but still use stock cooler in the radiator) gave me good results, the temp did drop down and reduced transmission slip especially when abused/long journey. But this also with upgraded power to the engine (stock 150hp, now 300hp++) so.. cooling system needs to be upgraded lol. I even upgraded the radiator to full alloy 3 ply

Since I don't intend to upgrade the power of the w212, I guess its ok to leave at stock. I read somewhere the one who has this issue mostly valeo radiators, someone recommended to switch to behr as it uses different design on sealing. Is that true? behr brand seems has pretty good price in local market place (but this also makes me suspicious ).

One more thing, I did read somewhere on this forum, I remember somenoe mentioned after replacing his radiator the transmission fluid keeps leaking, then he replaces the connectors since the connectors seems one time use.... is ths also true?

 

I don't know if Behr is better than Valeo for radiator.... no experience. I mean these radiators last 10+ years easy.

Our W212 engine bay and radiator section is already full-house , not much free room like a Toyota Kijang/Innova.
Good thing Toyota has many good aftermarket parts, unlike a W212.

Also W212 radiator stacking with condenser is kinda complex to mess with.

Next time use the Launch to see what is your tranny oil temp during long drive and long traffic jam.
Tranny oil is good at about minimum 60C, too cool is not good too for smoothness. We want it no more than 100C if possible.
My tranny oil is usually 80C, max 88C if really bad traffic jam. Uphill climb would effect tranny oil temp too for sure, but when I last went to Bromo in 2021, I do not yet have temperature sensor for tranny oil pan.



BELOW : Here is the last 8th hour run, after a fuel stop and into Surabaya city.
These are oil pan or DIFF body temperature using K thermocouple. It is not immersed in oil built-in temp sensor of the 7 speed tranny, as I can't get that data from OBD.


Tranny oil : 80C ish is the accurate one when at low speed in the city, where the oil pan does not get wind cooling effect of good 120KM/H or faster at highway.
At high speed, I will add 10C as actual tranny oil temp.
DIFF temperature is hotter at high speed, because I do not have DIFF oil cooler, the faster I go, the hotter it becomes from higher speed of the gears, but I never seen more than 92C.


FACTS :
My engine radiator is not good enough if I track the car in Sentul at 35C ambient temperature, by 3rd laps if driven hard, 120C is guaranteed.
For bad traffic jam or normal use even driven hard on the road, its fine.
MB engine cooling system algorithm and design is a "hot" engine at 95C typical, sometimes they push to 105C on purpose. Unlike Japanese max 85C - 88C typical.
Now you have OBD gauge, see how much a liar your analog coolant gauge needle is vs true data out of the OBD port.

If you can get genuine Behr and 100% compatible to yours, go for it.