Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSAUDI1998A8 SEDAN (4D2) V8-3.7L (AEW)REPAIR AND DIAGNOSISENGINE, COOLING AND EXHAUSTCOOLING SYSTEMSERVICE AND REPAIRBLEED COOLING SYSTEM
1998 Audi A8 Sedan (4D2) V8-3.7L (AEW)
Bleed Cooling System
1998 Audi A8 Sedan (4D2) V8-3.7L (AEW)SECTION Bleed Cooling System
1. Remove cap on expansion tank, attach adapter tool No. VAG 1274/1, or equivalent, and extend to 100 mm using 42 mm diameter (1-5/8 in.) hose.
2. Open vent screws at feed and return lines of heating system.
3. Add coolant until it flows from vent valves.
4. Close vent valves.
5. Re-install cover of expansion tank.
6. Disconnect 2-pin harness connector from pump unit.
7. Set heating/air conditioning controls to "LO."
8. Start and run engine at approx. 2000 RPM, for approx. 3 minutes.
9. Check fluid level in expansion tank and refill if necessary to max. level.
10. Re-connect 2-pin harness connector to pump.
11. Set heating/air conditioning controls to "Hl" and blower speed to lowest setting.
11. Start and run engine at 2000-3000 RPM for about 10 minutes.
12. Stop engine (switch ignition off).
13. Switch ignition back on.
NOTE:
^ When the heating and air conditioning controls are set to "Hi, " the electric pump to the heater must not make any noise.
^ Noise indicates that air is trapped in the heating system and requires the bleeding/venting process to be repeated.
14. If there are no unusual noises:
- Switch ignition off.
- Check expansion tank fluid level and refill if necessary.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.