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Filament jam and overheating extruder motor  

Active Member
Filament jam and overheating extruder motor


Lately its been impossible to print PLA for more than 3-4 hours because of filament jam. What could be the reason? I have disassembled and reassembled the extruder with a new PTFE and a collet clip. Still the same problem. 

One hypothesis is that the overheating (too hot to touch) motor is transferring the heat through the bearings to the PLA and softening it.

I have reflashed the firmware, increased the PLA printing temp to 220 (expecting a faulty thermistor) but to no avail. 

Maybe the pulled out filament offers some clues? 

It's important to add that the Mk3s printed like a dream for days on end before randomly and abrubtly starting to exhibit this jam issue. 

What could be done? 

There's a popular solution of printing a shroud and attaching a fan to the extruder motor, but I can't belive that to be the only solution to this!! 


Posted : 29/03/2020 7:37 am
Steph liked
Veteran Member Moderator
RE: Filament jam and overheating extruder motor

That looks like  squashed PLA, Could the bondtech tension screw be too tight? I remove the filament, then unscrew the tension screw until is comes loose and then press the screw in against the spring until it just catched the nut in the bondtech door. (Minimum tension) then reload the filament

the extruder motor is not supposed to get very hot, if it does the heat may transfer along the motor shaft and soften the PLA filament, this can also cause squashing and distortion of the filament

the heat generated inside the motor is supposed to dissipate into the air around the extruder motor. It is possible to reduce the motor drive current using Gcode commands, but I have never done this ! If you have not intentionally increased the motor current, then this should not be a problem... 

Have you done a firmware upgrade recently? it may be worthwhile going back to the old firmware and re trying the setup. 

Is your Print Gcode causing a lot of retractions, or are you using long retractions? I reduce my retractions to 0.4mm from the default 0.8mm retractions can cause higher temperatures in the motors. can you limit retractions to only when crossing perimeters? in Prusa Slicer

Are you using the latest version of Prusa Slicer@

Is the printer inside an enclosure? is the door closed, is the temperature elevated? 

Is the room the printers are located in, hot?  say  above 20Centigrade? 

if the spring pressure is not too high and the ambient temperature is not too high, I have no other ideas what may be causing this issue. 
a Fan shroud and fan may be a quick fix!

regards Joan



I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK

Posted : 29/03/2020 8:34 am
Active Member
Topic starter answered:
RE: Filament jam and overheating extruder motor

Here's another image of the pulled out filament after a jam

Posted : 29/03/2020 9:12 am
Peter M
Noble Member
RE: Filament jam and overheating extruder motor

Search on forum for movies/pictures for overheating motor, the filament should be getting wider , after a short piece.(and you find solutions for this).

Filament not good? (jams). I had filament that was bad , clogging wen printing. Try different brand.

Nozzle not clean, do a few pulls out of the filament.

If you extrude the filament, is the stream straight?



Posted : 29/03/2020 9:42 am