Three years back I was working as Ref. Eng in huge cold stores in UAE with FES ammonia screw compressors consisting of low, high stage and booster compressor for blast freezer. Compressors with liquid injection oil cooling system all comps use the same oil complying to that recommended by FES. One of the low stage compressors at -35 C started transferring all the oil to the coalser filter compartment and no oil recovered to the main oil receiver while other comps at the same conditions are working satisfactorily,all working conditions are normal(pressures, temp. etc) we checked oil recovery line and controls, ex. valve , oil pump replaced coalser filters and oil in vein. contacted the manufacturers but their recommendation had been done already. at last the recommended to replace the oil to their oil FES no 1, that was the solution, the problem disappeared, other compressors still with the other oil type and conditions working properly. I left the plant 2 years back but still could not interpret what happened