Project Guide

String Trimmer Maintenance

1
Safety First
A man adjusting a part on a string trimmer.

Before you perform any trimmer maintenance, be sure the power button is in the off position and the spark plug wire is disconnected. If you’re using a gas string trimmer, also make sure the gas tank is empty. 

2
Replace the String Trimmer Line

Whether you’re using a gas or electric string trimmer, replacing the line is an important part of string trimmer maintenance. You’ll need to do this regularly depending on how often you use your trimmer. Once the spool is brittle or depleated, the trimmer is less effective.


3
Clean the Parts
A dirty string trimmer full of grass clippings.
  • Once a season, give the exterior of your trimmer a good cleaning. 
  • Use a mix of water and dish detergent on the string trimmer head to clean off any grease, dirt and debris.
  • Locate the air filter cover and remove it to make sure the air filter is clean. Replace it approximately every 90 days, based on wear and tear.
4
Remove the Spark Plug
A person adjusting a spark plug on a string trimmer.
  • This should be done every three to four months, depending on use and level of dirt.
  • Empty the fuel tank, take off the spark plug boot and remove the spark plug using a socket wrench.
  • If the spark plug is brown, pour 1/4-ounce of engine oil into the cylinder.
  • Pull the starting cord several times to distribute the oil.
  • If the spark plug is black, it needs to be replaced.
  • Thread the replacement spark plug into the cylinder head and secure it in place using a socket wrench.
5
Empty the Fuel Tank and Change the Oil
Someone pouring oil into a string trimmer tank.

After you’ve used the trimmer for the last time in the season, empty its fuel tank. This must be done to keep the fuel lines and carburetor clear of fuel when not in use. For suggestions on proper fuel and waste practices, consult your local hazardous waste center. Check all screws and nuts, tightening as needed before storing your trimmer away.


With gas string trimmers, it’s important to check and add oil if the levels are low. Make sure to only add oil to the fill line. Overfilling the tank can damage the internal parts. You should also change the oil regularly. 


  • Let the engine run for a minute or two so the oil is slightly warm. This will make it easier to drain.
  • Disconnect the spark plug to make sure it doesn’t accidentally turn on while you’re working on it.
  • Unscrew the oil plug and carefully drain the oil into a container.
  • Once the oil has fully drained, refill the reservoir using the oil type specified by the manufacturer in the owner’s manual. The amount of oil required should also be outlined in the instructions.
  • Screw the oil plug back into place and reconnect the spark plug.
6
String Trimmer Storage
A backyard storage shed showing a string trimmer and other lawn tools.

At the end of the season, clean your trimmer thoroughly. Hose it down to remove any extra dirt and debris. Inspect the string and replace it if needed. It’s also best to oil the parts with a bit of lubricant to prevent rust and corrosion while it’s not in use.


Cordless string trimmers are generally easier to store since there are no cords to wrap or bundle. Some users prefer to hang them vertically in their storage space, while others prefer a horizontal setup. Whichever way you choose, make sure the area is cool and dry to prevent rust and corrosion. If kids or pets have access to the space, keep them higher off the ground and out of reach.  

Cleaning the parts, replacing the string trimmer line, inspecting the spark plug and changing the oil are all essential parts of any string trimmer maintenance routine. Shop our selection of outdoor power equipment today. The Home Depot delivers online orders when and where you need them.