I changed the rad on my 92 2.0 audi 80 last week, had the same trouble lol
What you have to do is.... Remove the exp tank filler cap and get a bottle of water ready. Then as you're looking at the engine, pull off the left hand pipe that goes to the heater matrix, (slacken the clip first lol) then push it upto the plastic part you just removed it from but leave a tiny gap right at the top
Then top up with your water untill it starts coming out of said gap. Then push the pipe all the way on and tighten the clip back up. Worked on mine
