Mineral Hydraulic Fluid

Ahh, what Audi maintenance pages could be complete without a section for that wonderfully expensive mineral hydraulic fluid known to most as Pentosin or "Goo 2000". (O.K., if you've got a model with vacuum assist such as a 4000 then you probably don't care.)  Pentosin is the brand name; they actually make many different fluids besides our mineral hydraulic stuff. If you buy it by the Pentosin name, you'll have two choices 7.1 (green cap) or 11S (red cap). I still haven't figured out which type the Coupe Q originally came with, but I use the 11S because it is a newer and supposedly better synthetic version (it's also more expensive). "Goo 2000" comes from the VAG P/N which is G 002 000. You'll see this number on the reservoir in the engine compartment. This is a completely different juice from hydraulic brake fluid. Many unsuspecting owners and mechanics have mistakenly topped up the Pentosin reservoir with brake fluid, only to have every seal in the system begin to weep with sorrow.

Ideally, you should never have to add this stuff. So, why did I put this under regular maintenance?  Well, slow hydraulic system leaks are a common failure on these cars. If your car groans while you are turning the wheel, it could mean that you have a pentosin leak. You could just keep adding fluid, but if the leak is big enough, you'll be spending a lot of money on fluid, and you could have a dangerous problem (see bomb). Lots of mail order places like GPR (800-321-5432) will give you a (relatively) good price on the fluid.


Flushing the hydraulic system every 25K miles or so will extend the life of many of the expensive hydraulic components, including the pump, steering rack, and brake servo. This is not usually part of the prescribed maintenance, so most cars are still running around with the original fluid (plus years of accumulated contaminants).

Begin by emptying the reservoir with a turkey baster. Then put the front end up on jackstands and turn the steering lock-to-lock a few times. This will purge the remaining fluid out of the rack. Pump the brake pedal until it becomes stiff. This will release pressure from the "bomb" and return more fluid to the reservoir. Once you've sucked out all the old stuff, clean out the reservoir with a degreaser and clean or replace the filter inside.

Now fill the reservoir to the top with fresh fluid and start the engine. The system will basically fill and bleed itself, so just refill the reservoir as the fluid is distributed through the hydraulic components. Once the system appears filled, slowly turn the wheel lock-to-lock to purge the last air bubbles out. You will initially hear some whooshing/groaning as the air is purged out, then the system should quiet down. The total capacity of the system is about one liter, but you should probably have two cans just in case you need more.

See also: Brake Problems

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