Air could get in around the bleeder screw threads.

The gravity method should work as well but it takes longer. Just open the bleeder and let the fluid flow.

Keep an eye on the resivoir. The rear one on my 87td is very hard to see, its only the last 1/2" or so of the tank and it doesn't fill until the front section is very close to the top.

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82 Rabbit diesel (first d), 84 Jetta turbo d (300k when sold), 83 240d (305k when sold), 84 F250 6.9d w/Banks turbo(parts truck), 86 F250 6 cyl.gasser(waiting for 6.9d), 84 300d ( 347k Sold 8/04), Y2k New Bettle TDI (185k miles), 95 740IL (wifes), 87 300TD (206k Sold 7/05), 05 Passat TDI Wagon