Car Doctor Q&A: A Rumbling Transmission in a 2003 Mercedes C320 4MATIC Wagon

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Spoiler alert: Any time somebody says “transmission” and Mercedes-Benz in the same sentence, it’s going to get pricey.

Q. I have a 2003 Mercedes-Benz C320 4MATIC wagon with only 64,000 miles on it. I purchased it new and it has always been serviced by the local dealer.

Recently I noticed a sporadic rumbling sound from the rear of the car and some less than smooth shifting at about 2,000 rpm. I took it to the dealer, who informs me that they suspect a leak from the radiator into the transmission and the repair involves a new radiator and transmission.

It seems that the problem often appears after the car is out of the 50,000 warranty period. I am told that the repair will cost more than $8,000 to repair and since the car is out of wafranty – too bad! Do you have knowledge of this problem existing in these cars and do you know if Mercedes Benz has acknowledged this problem with any recalls or repair memos?

Obviously $8,000 is a hard pill to swallow for me, but it would be a nice steady stream of income for Mercedes Benz dealers if this problem is widespread.


A. There was a problem with some radiators made by one specific vendor that would leak coolant into the transmission. Mercedes-Benz came up with a test to look for glycol contamination in the transmission fluid. Depending on the concentration, nothing would be done and it would be considered normal condensation. If the concentration was higher the radiator would get replaced and in the worst case the radiator and the transmission torque convertor were replaced.

Although Mercedes did issue a technical service bulletin there is no recall and extended warranty on this issue.

John Paul is public affairs manager for AAA Southern New England. A certified mechanic, Paul tests dozens of new cars each year and also hosts a radio show on AM 950 and 550.