My experience has been the same. Automatic transmissions use a thin layer of fluid between plates to create the friction surface, which as you can imagine, has a lot of heat generated. If the fluid is not synthetic, it breaks down even more easily. I have changed it in as little as 13,000 miles to find it to be seriously discolored. Black and junky after 44,000 miles on a Honda.
Originally Posted by TDIwyse
Thought some on here might be interested in this information.
Took the time yesterday to do some maintenance that I thought was appropriate, no matter what the official BMW stance is on the subject (3 year fuel filter change interval and “lifetime” transmission fluid . . . Both seem too long to me).
First attached pic is of the car up on the lift as the new fuel filter is beling flushed. Was curious if there was evidence of water trapped by the filter. Good news is no free water found. This could mean a couple things: 1) The truck stop used for >95% of fuel must do a good job of keeping free water from their tanks. 2) The fuel filter doesn’t do diddly for stopping free water. Hope #1 is the reason.
Second picture is a comparison of the old transmission fluid to the new fluid (ZF Lifeguard 6 as recommended by the transmission manufacturer). Was a bit surprised at the color and smell of the old fluid at <30,000 mls. Glad it was decided to do a fluid change this early. Considering not all the fluid gets refreshed with the approach used think a 2-3yr change interval will continue to be used on this vehicle.
The larger fuel filters found in TDI's seemed never to have any water when I drained them, nor did they need changing for at least 30K miles.
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