C230k 722.6 transmission fluid level changing too fast + mystery leak
Thread Starter
Senior Member
Joined: Jul 2011
Posts: 328
Likes: 56
2012 S350 Bluetec 4MATIC; 2011 ML350; 2005 C230k;
C230k 722.6 transmission fluid level changing too fast + leak from breather
I have mystery transmission oil leak. The leak is on right side. I already replaced the connector twice, also replaced o-ring for dipstick tube.
When I measure oil level at 80C the level is changing too fast. If I measure the level after short drive when I monitor the temperature with STAR at exactly 80C, it is exactly between Min and Max but 10 seconds later is above the Max line and 30 seconds later is already on silver part of the dipstick.
It is possible that oil pump is not working correctly and when engine is in idle, the oil pressure is too low and the transmission fluid level is increasing and then I have leak from the breather which is on top of transmission?
The leak is not from bellhousing or connector and it is on right side.
I don't have any issues, it is shifting nicely.
When I measure oil level at 80C the level is changing too fast. If I measure the level after short drive when I monitor the temperature with STAR at exactly 80C, it is exactly between Min and Max but 10 seconds later is above the Max line and 30 seconds later is already on silver part of the dipstick.
It is possible that oil pump is not working correctly and when engine is in idle, the oil pressure is too low and the transmission fluid level is increasing and then I have leak from the breather which is on top of transmission?
The leak is not from bellhousing or connector and it is on right side.
I don't have any issues, it is shifting nicely.
Last edited by artim808; Jun 14, 2020 at 01:12 AM.
Thread Starter
Senior Member
Joined: Jul 2011
Posts: 328
Likes: 56
2012 S350 Bluetec 4MATIC; 2011 ML350; 2005 C230k;
The leak is from top breather. Now the question is what can cause the oil level increase to the level when is actually start leaking. Can defective radiator with reduced oil flow cause high oil level?
Super Member
Joined: Sep 2016
Posts: 571
Likes: 92
From: New England! :-)
2005 C230K Sport Coupe
First, it's typically called Transmission Fluid. By saying "oil", it's very confusing. 
Check your anti-freeze level.
It sounds like your radiator has a leak between the transmission cooler section of the radiator, and the anti-freeze section of the radiator.
That's a known problem with some MB radiators.
Since you see such a noticeable change after 10 seconds, another thing you can do is to drain the anti-freeze, wait for the engine to be at ambient(outside) temperature, then run the engine for 30 seconds, and only 30 seconds - not more.
If the engine is cold - outside temperature. You can run the engine for 30 seconds without any anti-freeze. It takes time for the thermal mass of the engine to gain significant heat.
DO NOT RUN THE ENGINE FOR MORE THAN 30 Seconds. And, only do that when the engine is ambient temperature.
Note: The Temperature gauge is not accurate when there isn't any anti-freeze, and hot spots develop quickly.
Good Luck!
Check your anti-freeze level.
It sounds like your radiator has a leak between the transmission cooler section of the radiator, and the anti-freeze section of the radiator.
That's a known problem with some MB radiators.
Since you see such a noticeable change after 10 seconds, another thing you can do is to drain the anti-freeze, wait for the engine to be at ambient(outside) temperature, then run the engine for 30 seconds, and only 30 seconds - not more.
If the engine is cold - outside temperature. You can run the engine for 30 seconds without any anti-freeze. It takes time for the thermal mass of the engine to gain significant heat.
DO NOT RUN THE ENGINE FOR MORE THAN 30 Seconds. And, only do that when the engine is ambient temperature.
Note: The Temperature gauge is not accurate when there isn't any anti-freeze, and hot spots develop quickly.
Good Luck!
Last edited by RedGray; Jun 14, 2020 at 12:49 AM.
Thread Starter
Senior Member
Joined: Jul 2011
Posts: 328
Likes: 56
2012 S350 Bluetec 4MATIC; 2011 ML350; 2005 C230k;
Funny thing is I recently replaced radiator with Nissens brand just to prevent the internal leak since I had original Valeo radiator. Do you think the new radiator can be defective and have reduced transmission fluid flow, which is causing the leak? Sorry for confusion with the oil, next time I'll use only word fluid.
Last edited by artim808; Jun 14, 2020 at 01:05 AM.
Super Member
Joined: Sep 2016
Posts: 571
Likes: 92
From: New England! :-)
2005 C230K Sport Coupe
Does the transmission fluid level go done after you turn if the car?
If so, how long does it take? Just approx like: less than 1 min, ~5mins, hours+).
I don't know the fluid path in the MB tranny. I'd be surprised if it would raise the level. The fluid has to come from somewhere, and go somewhere.
Good Luck.
If so, how long does it take? Just approx like: less than 1 min, ~5mins, hours+).
I don't know the fluid path in the MB tranny. I'd be surprised if it would raise the level. The fluid has to come from somewhere, and go somewhere.
Good Luck.
Thread Starter
Senior Member
Joined: Jul 2011
Posts: 328
Likes: 56
2012 S350 Bluetec 4MATIC; 2011 ML350; 2005 C230k;
I'll have to check that. Maybe the pump is defective and cause the leak, but the transmission is shifting fine, if the pump is bad I would expect to have issues with shifting.
Super Member
Joined: Sep 2016
Posts: 571
Likes: 92
From: New England! :-)
2005 C230K Sport Coupe
The pump in the tranny takes fluid from the pan, pressurizes the fluid, sends the fluid through-out the tranny (controlled by valves/etc), then to the radiator to be cooled, then the fluid flows back down into the pan.
It's a closed system.
There's a vent for the pan/fluid, because it's not in a temperature-controlled vacuum. So, the air pressure(area) increases (when it gets hot), and reduces when it gets cold.
Good Luck.
It's a closed system.
There's a vent for the pan/fluid, because it's not in a temperature-controlled vacuum. So, the air pressure(area) increases (when it gets hot), and reduces when it gets cold.
Good Luck.
