How much oil is required when changing the oil and filter in a 1998 VW passat sedan 1.8L turbo? I've also heard that there is a oil slugde problem with those engines, are there any additives or solutions to resolve the build up of oil sludge?

1998 VOLKSWAGEN PASSAT 1.8L 4-cyl Engine Code AEB/AWM Turbo
Models with 1.8L Engine codes AEB, ATW, AUG, AWM only
use engine oil that is formulated to meet
Volkswagen oil standard VW 502.00
(with viscosity of SAE 5W-40, 5W-30 or 0W-40).

CAPACITIES: Engine, with filter..........3.5 liter To prevent overfilling during oil changes, add 0.5 liter
(0.5 quart) less than capacity shown, start engine, let run
until engine operating temperature is approx. 60 °C (140 °F)
, switch engine off, wait 3 minutes, check dipstick,
fill to full mark as indicated on dipstick (may be more or
less than 0.5 liter (0.5 quart) depending on model).

As for the sludge question, I add Marvel Mystery Oil around 600 miles before i do my oil change. This will clean out the oil pick up screen and oil journals through out the engine, I do this on every oil change and i have over 356,000 miles on my engine. Oil and filter changed every 3,000 miles intervals. Good luck and hope this helps.