Why is my M18 trimmer going through so much line?

Start with the spool. Wind the line in the direction marked on the head, keep steady tension as you wind, and make sure the turns sit neatly instead of crossing or bunching. A loose or uneven wind can jam when the head tries to feed. Also check the head’s markings for the correct line size and loading length, and don’t pack in more than it calls for.

If it keeps happening, try a short test with the line that came with the trimmer or another line listed as compatible. Different line can behave differently in the same head.

Check whether the line is simply too long. If the guard is meant to stay on, keep it installed so its cutter can trim the line to length. Longer line can add strain, and bumping the head repeatedly can send out more than you need.

There are a couple of possible culprits here, so I wouldn’t assume every line brand will behave the same. Some reports point to line binding in the head, while others describe the supplied line working better for them. I’d verify the diameter against the head’s instructions, then try a small amount of a known-compatible line before buying a big spool or replacing the head.

If correctly loaded line still jams, inspect the spool and head for damage or a rough edge that could catch it. If the trimmer is also cutting out, that may be a separate issue rather than just line consumption.