I have a machine I built myself using the plans found in the book Printing in Plastic from www.buildyourcnc.com.

It essentially has the same specs as a Makerbot Thing-o-Matic although the extruder is a MK7.

I'm printing at about 205 F and extruding at a flow rate of 1.98 (this per the setup instructions from the book's author / printer's designer).

I have very good success printing for up to one hour. Once I hit that point, I start having extrusion problems. I've tried tweaking the tension on the extruder to no avail. What it appears is happening is that the heat is traveling up the filament over time and causing the filament still being pushed by the drive gear to soften.

I have the basic OOTB heat sink and fan that came with the extruder.

Does this theory seem plausible and if so, are there any tips on bleeding away the excess heat?