cdg

Does anybody know the normal operating temp range for the 722.9 transmission in the earlier W212 E550s? Thanks in advance!

S-Prihadi

75 - 77 Celcius, by this temperature the thermostat will open and allow tranny oil cooler to flow and cool the oil.
I am at a country with ambient of 30 - 32C all year round.
Hottest I seen would be 88C, at traffic jam after exiting highway....so less wind speed and its all by radiator fan cooling.
If you see at 100KM/H or higher, 72 - 75C is what I get, while ambient temperature is 32C.

Here is my log for your comparison

cdg

I took the car out and monitored the transmission temp for about 20 minutes. The car was already warm. I eventually did a few hard pulls and reached low 90s. When I started driving it went from mid 70s and remained in the high 70s/low-mid 80s. Does this seem about normal?

I see yours did not even touch 90. May need to redo my transmission service… I followed the procedures but a buddy told me the trans fluid pan bolts are one-time-use only. I did replace the drain plug, washer, filter, etc. because I got the FCP Euro kit.

S-Prihadi

First I have to explain what type of temperature sensor I am using for tranny and where I am reading at.

I am using a thermocouple K type, at the skin of the tranny oil pan.
I am not using MB Xentry or semi-pro scanner which can read also tranny oil temperature.

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DO NOT use OBD2 type generic bluetooth dongle ELM 327 and Apps like Torque Pro for tranny oil temp, MB does not send out such tranny oil data over OBD2, but some Apps like
Torque Pro has the PID and it is not reading tranny oil, it reads coolant temperature albeit the PID name is tranny oil.
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The thermocouple end




Insulation 3mm HVAC foam, to prevent wind at cruising speed cooling down the K thermocouple.




Now, MB Xentry or any proper scanner will read oil temperature sensor INSIDE the tranny, it is usually a tiny bit hotter than my thermocouple, unless at traffic jam and car is moving like a turtle and been so for 5+ minutes.
At cruise speed, my tranny oil pan regardless it is covered by MB plastic undercarriage shield, the thin metal oil pan itself get a bit cooled by the wind velocity, so I would add maximum 5C to my logged data to equal
MB internal tranny oil temperature sensor.


You did not say what is your ambient temperature during those test you did. This matters too.

I would say 90C ish read by MB internal tranny oill temperature sensor is rather hot if your ambient temperature say is 20C or cooler.

Now, if you have a thermocouple type stand alone sensor like found on Fluke DMM, you can use it as a comparison data, just in case your MB internal tranny oil temperature sensor is drifting its value at higher temperature.
Read it immediately when you reached home after a drive longer than 30 minutes. I would not rely on infrared type temperature gun.

At the least, if your engine been killed 24 hours or more, tranny oil temp would equal ambient temperature and that is also a way to test its lower temperature reading/value.