Latest Reader Q (Oct. 7, 2017)

Here is the latest reader question, along with my reply:

Gerhard asks: I read your article today about transmissions on the Lew Rockwell site.  My auto is a 2000 CLK430 Mercedes. The service department has always told me that my transmission has permanent fluid and should and cannot be changed.  I have about 176,000 miles on the car.  The engine has no dip stick for the transmission. Most likely you are familiar with this type of transmission. Since I have been told that it is not necessary to change the fluid, will I encounter a transmission failure in the future? Would appreciate your expert opinion on this.

My reply: Mercedes, like many other automakers, advertises that certain usually serviced/replaced items are “long life” or even “lifetime” or “permanent.” However, nothing lasts forever – not even the Earth and sky. And certainly not hydraulic fluid (or engine oil or coolant) and even if they did, they will become contaminated over time – which is the main reason for changing out fluid.

Also, filters.

Which have a finite capacity to  . . . filter.

Eventually, they become saturated with the particles and so on they were designed to filter out and, when that happens, they lose their ability to filter. In which case, the fluid circuit is often designed to simply bypass the filter. Which isn’t good for the obvious reason that you are now driving around with unfiltered fluid.

So, even though Mercedes may not recommend or even specify periodic fluid/filter replacements, if it were my car, I would do so regardless for the reasons just outlined. As for the interval, I would do it every 50,000 miles or so, if it were my car. And particularly if my car happened to be a Mercedes as a replacement transmission will be very expensive.

PS: Mercedes (and BMW) have electronic fluid level monitors that can be accessed via (in your case) the COMAND interface. I personally prefer a physical dipstick because there’s no chance of an erroneous reading; the fluid is either at the right level on the stick – or not.

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