extruder stops extruding during long print

I have a Makerfarm Prusa i3 8" with the Magma hot end, printing 3mm ABS. It's been working well, steady progress improving my prints and learning about the hardware and software. A couple days ago I added the "hot end fan shroud" [www.thingiverse.com] and it made an immediate improvement in my prints, noticably reduced warping and more stable bed temps. Today I started a longer print, about 3 hours. Everything ran fine for the first 2.5 hours and then i noticed that the extruder might not be putting out quite enough material, but wasn't sure. Checked on it 10 minutes later and it had stopped putting out material all together.

I haven't torn into it yet but I was wondering if anyone else has experienced this. The nozzle isn't clogged because after I killed the print ABS was oozing out of the nozzle normally while it was still hot. My instincts are that the fan wasn't running at high enough RPM and therefore wasn't pulling enough heat off the fins for the hot end, allowing heat to leak up and melt the filament too high up, but that's just a guess.

Thanks in advance for any thoughts and insight.

Steve

I don't know if this will help, but on mine if my fan setting is too high it will prevent it from extruding. It will say cold extrusion prevented in pronterface. I know this is a simple thing that you most likely have already checked but just thought I would add and hope helps.

It took me a while to figure out the right settings in slic3r before I got the right settings and I'm still calibrating.

V/R

ND