Mag Drive 12 in-line or not?
 

I just purchased a new mag drive 12 should I use it in-line or should I put it in yhe sump? I'm worried about heating

I have a Mag 12 as my return right now. I put it inline and discovered there was a small crack in it so I tossed it into my sump. Seems to be going fine and no overheating (yet). Of course it hasn't been in there during the summer, sooooo....

I have a MAG 12 and an 18 in my sump and I have no problems with heat. This was also the setup when it was a 75g tank.

My Mag 12 is in-line and I regret that choice. I'd recomend submersing it and if heat becomes a problem next summer then you might try in-line.
It's not unbearably noisy but it kinda' "clatters" as if there's air trapped in the impellar housing. I have a 60g "diamond" shaped tank so the cabinet space was very limited. I suspect that because there is a low/limited water level in the small (10g) sump that the inlet "pressure" is low resulting in a "cavitation type" noise... :?
Four years running and still I think it's a good pump though.