Coolant Flush

Safety
Anti-freeze is a dangerous substance. DO NOT leave anti-freeze on the floor or in a pan around animals or young children! It has a sweet flavor, but it is deadly! If consumed, it will cause a slow and painful death. There are non-poisonous brands of coolant on the market, but don't ever take chances if there is any doubt.

Coolant Drainage (Dave Kase)

• If engine is warm (just shut down):
  Unhook the lower main radiator hose while the engine is still fully warm. At this point the thermostat is open and the block water will drain through the main rad. The thermostat is open if all the radiator hoses are warm (remove cover in front of main rad to get to hoses). This should be done as soon as possible after the engien is shut down. If only 3-4 quarts of coolant come out, the thermostat is closed and the block will still have coolant in it.
• If engine is cooled down:
  The Bentley says to drain the engine by disconnecting the lower main radiator hose and the heater hose from the engine. The heater hose connection is buried so disconnect the left hose from the firewall heater connection. Then lower the hose below the block connection to drain the block. This method is a bit messy as the coolant drains through some components under the hood.

Coolant Refill (Dave Kase)
Audi specifies only phosphate-free anti-freeze be used. Open bleeder valve on heater hose where it goes through the firewall. It may be difficult to get flow here until the car is started and the level in the coolant tank goes down. Then replenish the tank and when the engine gets warm. It should start to flow out of bleeder.

Coolant System Overhaul and Thermostat Redo (Dave Kraige ala Bernie Benz&Peter Kirby)
A detailed account with many photos.

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