legoman is using a 317 gallon per hour eheim and his oil is only a few degrees above room temp IIRC. the diaphragm pump i posted is 3 gallons per minute, or 180 GPH. and thats the rating at 60 PSI, which i dont imagine youll be anywhere near...so your flow should be considerably higher. if worst comes to worst, get 2! keep in mine, ANY pump you buy can be submerged...mineral oil is non conductive id imagine the performance loss in drag as oil seeps into the motor should be minimal with the relatively low-drag an armature produces (compared to a PC fan) and a high torque motor like youll find on any pump. i do agree the roller style pump would look sweet in there. maybe lit with red LEDS so it looks like a mechanical "heart" pumping "blood". unfortunately i think youll have a hard time finding a pump of that style that moves a significant amount of liquid.