Engine coolant in transmission
Thread Starter
Junior Member
Joined: Aug 2020
Posts: 40
Likes: 16
From: Danville, CA
2013 E350
Engine coolant in transmission
I recently experienced an overheating problem. The car was towed to the local MB garage.
It was misdiagnosed as an oil cooler seal failure. Oil cooler was replaced. Coolent pressure tested - held pressure.
Test drive experienced extremely hard shifting (never had this problem), then they dropped the pan to find coolant in the transmission oil.
The radiator / tranmission oil cooler had failed allowing coolant into the trany.
I am now told it shifts very hard after flushing it multiple times and installing a new radiator.
Anybody ever have this problem?
The car has perfect maintenance record, no coes. This just happened out the blue!
It was misdiagnosed as an oil cooler seal failure. Oil cooler was replaced. Coolent pressure tested - held pressure.
Test drive experienced extremely hard shifting (never had this problem), then they dropped the pan to find coolant in the transmission oil.
The radiator / tranmission oil cooler had failed allowing coolant into the trany.
I am now told it shifts very hard after flushing it multiple times and installing a new radiator.
Anybody ever have this problem?
The car has perfect maintenance record, no coes. This just happened out the blue!
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Joined: Oct 2005
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See post #14 in this thread regarding the Torque Convertor clutch:
https://mbworld.org/forums/mercedes-...r-failure.html
https://mbworld.org/forums/mercedes-...r-failure.html
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Joined: Jun 2020
Posts: 1,363
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'11 E350, '11 E550, '98 M3, '95 E320
Back when you were experiencing an overheating condition, you did some troubleshooting. Did you ever notice a "sheen" in the reservoir on the coolant surface? Unfortunately the combination engine/trans cooler MB has used for decades poses this risk if/when it fails. I've seen plenty of failed radiators in my time working on MBs and typically they start leaking at the crimped ends... these are on cars that are 10/100k+ (year/miles) made between the 80s and early 2000s. I doubt the newer radiators are constructed any differently. I can't recall many, that had failed "internally" causing a mix of fluids... but, things happen.
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Joined: Jun 2020
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'11 E350, '11 E550, '98 M3, '95 E320
It started hard shifting after they replaced the oil cooler [and seal] and pressure tested the coolant system? Seem coincidental.... however them replacing the oil cooler for a sporadic overheat doesn't make sense either to me. If anything, the seal leaking [oil] is a common issue on M272/273, not sure if the M276 shares the same design.
The trans fluid has been flushed a few times, besides checking codes, maybe they should try to readapt the transmission, like this:
The trans fluid has been flushed a few times, besides checking codes, maybe they should try to readapt the transmission, like this:
Thread Starter
Junior Member
Joined: Aug 2020
Posts: 40
Likes: 16
From: Danville, CA
2013 E350
Thanks for the great comments. Yes, it was readapted, still hard shifts, and slipping, unlike before the repair.
I am wondering if I should just swap out the tranny how to avoid the next failure.
I am wondering if I should just swap out the tranny how to avoid the next failure.
MBWorld Fanatic!
Joined: Dec 2005
Posts: 1,055
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From: SoCal. Desert
'16 E350, gone: '03 c230k
I know this doesn't help, but for posterity's sake will post that the ~2003 MY series of c-class cars had a well documented issue with one version of the radiator mixing the tranny fluid and coolant. In all the cases I read, the tranny was fine after being flushed.
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From: Orbiting the planet
This place is a joke.
Find another shop that knows what they're doing. This is an uncommon occurrence but it happens on the 212 chassis. Your transmission is ruined from the glycol. No amount of flushing will save it. Several other components of the cooling system also are ruined by the transmission oil. This requires an extensive repair costing approx. $10k-$12k at the dealership.
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Super Member
Joined: Nov 2011
Posts: 973
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From: Austin, TX
2013 SL550 BiTurbo
Find another shop that knows what they're doing. This is an uncommon occurrence but it happens on the 212 chassis. Your transmission is ruined from the glycol. No amount of flushing will save it. Several other components of the cooling system also are ruined by the transmission oil. This requires an extensive repair costing approx. $10k-$12k at the dealership.
If you're concerned about a possible future failure, you can run an aftermarket transmission cooler and just remove the lines from the radiator and run extensions to the new cooler.
When I was a tech in the 2000's, we did have issues with certain radiators. I changed many under warranty and a few that were found during servicing. Never had a transmission fail, but I know we did have other techs that did have total failures in some of the transmissions on cars that came in with bad leaks. Afaik, the issue was fixed then as I didn't see any more failures after we addressed all the bulletins/vehicles and replaced all the bad radiators.
Good luck!
Last edited by nota_amg; Feb 18, 2021 at 11:48 PM.
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Joined: Feb 2021
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1983 Nissan SHlTBOX
Piping and mounting the cooler was about as simple as it gets. I haven't even wired up the fan and the tranny stays at or below coolant temp. Do you think the W212 would be safer in the long-run with an external cooler? Do you believe the risk factor is high enough to warrant an external cooler as a safety measure? I want to keep mine forever, and I'd rather not have to replace a $7k tranny that should last the life of the vehicle. Thanks!
Super Member
Joined: Nov 2011
Posts: 973
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From: Austin, TX
2013 SL550 BiTurbo
I feel it's absolutely safer with an external trans cooler. There is NO WAY it can fail and mix the fluid if they are seperated. It doesn't seem to be a huge problem, but it certainly won't hurt anything either.
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Joined: Feb 2021
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1983 Nissan SHlTBOX
I agree. I really like the Mishimoto cooler that I have on my Maxima. There's also plenty of space between the condenser and the front bumper cover/grille. I'll poke around and look into it. First thing on my list with this new car is timing chain tensioners and cam solenoid O-rings. I have the dreaded oil leak on both banks at 85k on mine and it has never been done. I may order a passive heat exchanger rather than a fan-cooled unit for the Benz.
Thread Starter
Junior Member
Joined: Aug 2020
Posts: 40
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From: Danville, CA
2013 E350
Thanks Senecan and nota amg, the local shop did the work and installed the OEM radiator with integral trany cooler. I'll see if there is room to install the Mishimoto cooler. I believe there is. They also installed new cam solenoids and o-rings as mine were leaking. 84k mile on it now.
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Joined: Feb 2021
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1983 Nissan SHlTBOX
That's fantastic! I have the exact mileage on mine. I just started a thread regarding solenoid seal replacement last night. I'll be doing the work myself and documenting it to finish the DIY thread.
https://mbworld.org/forums/e-class-w...ls-repair.html
https://mbworld.org/forums/e-class-w...ls-repair.html
