S-Class (W220) 1999-2006: S 320 CDI, S 320, S430, S 500, S 600

Why may cars transmission strain when the car reaches 90c?

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Old Aug 21, 2018 | 10:23 AM
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Mercedes S430
Why may cars transmission strain when the car reaches 90c?

2002 S430 Mercedes Benz. I have change the water pump, flush the radiator and replaced thermostat. The fan kicks on near the 90c mark. When the car reaches the 90c mark the transmission strains in the 1st and 2nd gear. At 80c the car runs fine.
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Old Aug 21, 2018 | 01:13 PM
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Hey, I might be wrong but your radiator cools transmission oil as well. And based on your work with "cooling stuff" you either did something wrong or damaged something and now transmission aint getting cooled.
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Old Aug 21, 2018 | 01:40 PM
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Originally Posted by BigArt
2002 S430 Mercedes Benz. I have change the water pump, flush the radiator and replaced thermostat. The fan kicks on near the 90c mark. When the car reaches the 90c mark the transmission strains in the 1st and 2nd gear. At 80c the car runs fine.
ok first of all Why did you flush the coolant and water pump and thermostat ? Was there an overheating problem or other issue ?

the transmission cooler is built into the radiator . You might have a bad radiator
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Old Aug 21, 2018 | 01:44 PM
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Car running hot

This problem has going on for a while. Change pump and flush radiator because i thought that was the problem. The thermostat was change about a year ago. The transmission fluid have been changed also.
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Old Aug 22, 2018 | 02:15 AM
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Flushing a bad radiator doesn’t fix it . You probably still have a bad radiator even after the flush
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Old Aug 22, 2018 | 10:02 AM
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Modern vehicles, including your W220, are designed to operate at a coolant temperature of 90 deg C.

This brings up several possible questions...
Is the coolant temp gauge correct?
Is the transmission cooler operating correctly?
Is the coolant circulating correctly?
Is there another problem with the transmission that causes it to malfunction at what should be its normal operating temperature?
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Old Aug 22, 2018 | 12:00 PM
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most cars have barely enough cooling.In the days of ordering a towing package you got more rows in the radiator,and extrenal trans cooler. The w140 with large v12 even cooled trans seperate in the cool air. I use a extra cooler with my 722.6xx,I don't want trans temp to be radiator temp.
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Old Aug 29, 2018 | 01:10 PM
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I have replaced the radiator, water pump and thermostat. Filled with water the temp gage stayed between 80 and 85c. Drained the water and added antifreeze temp gage goes back to 90c. When car reaches 85 to 90 c the trans mission starts to strain in sec and third gear. If the car remains at 80-82 trans run fine.
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Old Aug 31, 2018 | 03:32 AM
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Originally Posted by BigArt
I have replaced the radiator, water pump and thermostat. Filled with water the temp gage stayed between 80 and 85c. Drained the water and added antifreeze temp gage goes back to 90c. When car reaches 85 to 90 c the trans mission starts to strain in sec and third gear. If the car remains at 80-82 trans run fine.
get a lower temp thermostat
also called a tropical climate thermostat
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Old Sep 4, 2018 | 10:03 PM
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maybe air got trapped inside?
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