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Tech Article

Audi C5 A6 Transmission Detergent Additives

Last Updated: 03/19/2017
Parts Group: Transmission oil pan
This article discusses the transmission oil pan for the C5 Audi A6 (1999 through 2004) with the ZF 5HP-24A transmission, with the focus being on detergent additives that people add to the transmission. If you're not here for the technical analysis but would rather buy a used transmission oil pan from us, guaranteed to work and fit, then please select one of the links below.The information herein is based on a project car that we bought. We removed the transmission oil pan, and we were puzzled to see that, except for right below where the magnets were, the black paint inside the pan had been eaten away. There was also a weird, filmy black, mess at the bottom of the transmission pan. Eventually it occurred to me that whatever detergent a previous owner had added to the oil pan had eaten away the paint, and the black, icky residue was the chemical remnant of the black paint. I dont't even want to imagine what so aggressive a detergent probably did to much else inside the transmission, such as the seals, and how the fine passages inside the valve body might well now be blocked with gunk.

Owners presumably pump detergent additives into their Audi's transmission pan fill hole, as a desperate measure once it's started slipping, typically in the first four forward gears. The classic failure pattern is when the pressure regulator has finally, after 15 years or so, worn out enough to allow a pressure spike through and blow out the rim of the clutch "A" drum. This was the case for our project car, too.

That's a mechanical failure, as in metal has separated from metal, and no amount of detergent will fix that. You might as well go snap a piece of aluminum in two and then pour detergent over it, hoping it'll fix the problem.

So, for the classic failure pattern, detergent won't help. However, it can hurt. Audi published a document specifically for those stuyding this type of transmission, and early on there's a picture of a big red exclamation point, a hand showing "Stop!" and the legend: "Additives cannot be added to the Automatic Transmission Fluid."

What adding detergent can do is waste your time and money, and reduce what little resale value you could get for your car if you decide to sell it. A failed-and-contaminated transmission is far more daunting a prospect than simply a failed transmission. If you were planning to keep the car, then you might well find out that the cost of a transmission rebuild probably will be higher if everything inside the transmission has been chemically contaminated. The contamination isn't limited to the transmission, either. The cooler lines and the inside of the radiator will also have been contaminated.
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