I made a test lava pool and placed a pump on it's center, the pool is 65 blocks of radius (from the pump ofc), I've chosen this value because I've observed that the pump reaches 65 blocks straight before start draining from the sides, so I guessed it would search for 65b radius.
Well to get faster results I've set the pump with the following upgrades: 10 Transformers, 64 EU Storage, 3 Fluid Ejector, 8 Overclocks. The pump is being fed with 8192EU/T.
If you look at the screen shots you 'll see the pattern it makes, and it seems random, you 'll also notice the amount of lava it drained before halting. IDK why it halts, maybe someone can tell.
Each Screen shot is a single test I made.
Also, idk why it always goes to WEST, tried placing the pump while looking towards elsewhere and same happens, GO WEST YOUNG!