Do Weed Eaters Need Oil?

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All gas string trimmers – including the Weed Eater brand – require oil. You have to add the exact amount of oil and gas specified by the manufacturer. The wrong amount of fuel can cause permanent engine damage.

A 2-cycle weed eater requires a 40:1 mix of gas and oil, which is 3.2 ounces of oil per 1 gallon of gas. Some 2-cycle models prefer a 50:1 mix however. You do not need to mix oil and gas in a 4-cycle trimmer as they are stored separately.

“Weed eater” is synonymous with string trimmers. Strictly speaking it is a brand that manufacturers a type of string trimmer. In this article I will use weed eater in refer to all string trimmers, as its requirements are similar to those of most trimmers.

What Oil to Put in a 2-Cycle Weed Eater

If you have a 2-stroke model such as the PowerSmart String Trimmer, you have to mix gas and oil. The typical ratio is 40:1 but 50:1 are used by other brands to this day.

Use whatever fuel the manufacturer suggests. This information will be in the operating manual. For instance, the Weed Eater brand recommends Poulan, Paramount or their own proprietary oil. If you cannot get those, use premium 2-stroke motor oil. In fact the company specifically states not to use any ordinary car oil.

Some 2-cycle string trimmers run on regular unleaded and motor oil. Just make sure to mix them according to the recommended ratio. Even a slight ratio error can prevent the engine from starting.

No matter what fuel you use, it has to be octane 87 and 10% or less ethanol. If you can get ethanol-free fuel that is okay too.

Aside from mixing oil and gas correctly, you have to make sure the air to fuel ratio is correct. Otherwise you run the risk of an engine flood.

How to Mix Weed Eater Oil and Gas

Your 2-cycle string trimmer comes with a container for blending the oil and gas. Do not mix the two in the fuel tank.

In this example I am assuming the string trimmer uses a 40:1 fuel mix. You need 3.2 ounces of oil for every 1 gallon of gas. Adjust the amount if the trimmer uses a different ratio..

Pour the oil and gas in the container. Close the lid and shake it well. Pour the mixed fuel in the fuel tank. I suggest shaking the container a few times to ensure the oil and gas are well mixed This video shows how to mix oil and gas for various small engines including weed eaters.

What Oil to Put in a 4-Cycle Weed Eater

4-cycle string trimmers do not mix oil and gas. There are separate fuel tanks for each, so it is easier to use. Simply pour the amount of gas and oil recommended by the manufacturer and the engine should be ready to go.

A lot of weed eaters run fine with regular unleaded gas, but it check the owner’s manual to be sure. Aside from the fuel, make sure the string size is correct.

With other brands it is the opposite. You can use the regular unleaded gas and motor oil you buy for your car.

If there is no specific fuel brand mentioned, it is safe to assume you can use regular car oil and gas. I have used a lot of string trimmers and never had a problem with regular unleaded gas. Just make sure the ethanol is no more than 10%.

If you are going to use regular unleaded, make certain it is octane 87. Some weed trimmers accept higher octane but others do not. Refer to your manual.

How to Fix Weed Eater Oil and Gas Problems

Adding oil and gas on string trimmers is straightforward, whether it is a 2 or 4-stroke model. But problems can arise due to incorrect mixing, old fuel and so on. I have compiled this list of common weed eater fuel problems and how to fix them.

Engine is smoking or too hot. If you have a 2-cycle string trimmer, it is probably due to an incorrect mix. Engines are sensitive to fuel and even if it is slightly off, will cause problems.

If you have a 4-stroke weed trimmer and the engine smokes, there could be other reasons. Since you don’t have to mix oil and gas, it could be due to old fuel. Or some engine component needs to be cleaned or replaced.

Engine will not start. There are many reasons why this can happen, but using the wrong fuel is one of those. This can affect 2 and 4-cycle weed eaters. Some common fuel related causes are:

  • Old fuel
  • Wrong gas and oil mix ratio
  • Incorrect fuel to air mixture
  • Fuel is too rich
  • Fuel is too lean
  • More than 10% ethanol in the fuel

Old fuel. Replace the gas every 30 days or put STP Ultra 5 in 1 to prevent it from turning gummy. Or you can just drain the fuel tank. If you’re not going to use the trimmer for a while, drain the tank.

Wrong fuel mix. Even the most seasoned gardeners make mistakes. If you suspect this is the case, empty the tank and mix fresh gas and oil. No matter what brand you use, you have to get the mix ratio right.

Wrong fuel to air mixture. If there is too much fuel in the mix and not enough air, the mix is too “rich”. If there is too much air and not sufficient fuel, it is too “lean”. Engine flooding usually occurs when the mix is too rich.

You can adjust the fuel to air in the carburetor. You have to turn the carburetor adjustment screws until the engine runs properly.

Too much ethanol. Be careful if you use the same fuel for your car and weed eater. Most cars today can handle up to 15% ethanol but weed eaters cannot. Do not use that fuel on any small engine because it is going to cause permanent damage.

Weed Eater Fuel Reminders

Always follow what the operating manual states. For example, don’t just assume the fuel mix is 40:1 for your 2-cycle weed trimmer. It’s true most models use that, but other manufacturers recommend 50:1 or something else.

Do not mix oil and gas in a 4-cycle weed eater. 4-cycle trimmers have two tanks for oil and gas. The 2-cycle models have just one to mix both. If you mix the fuel in a 4-stroke model it can cause serious engine damage.

Engines hate moisture. Wipe the machine thoroughly and store it in a dry place. This is particularly important if you are going to store the trimmer during winter.

To store a 2-cycle string trimmer, wipe the debris and drain the fuel tank. Now get a gas can and pour a small amount of gas and oil into it. Use the same mix ratio that your 2-cycle engine does. Do not pour the mix into the fuel tank.

Put fuel stabilizer in the gas can. Close the lid and shake it. Pour this mix into the 2-cycle trimmer fuel tank.

Turn the string trimmer on. Let the engine idle until it runs out of fuel. What you’re doing here is spreading the fuel stabilizer throughout the engine. After the fuel runs out, disconnect the spark plug. You can store the weed eater now.

If you have a 4-stroke string trimmer, remove the debris and drain the gas tank (remember, 4-cycle engines have separate tanks for gas and oil). Put the fuel stabilizer in the gas tank. Turn the string trimmer on and let the engine run for 10 minutes. Shut the engine off and give the fuel stabilizer half an hour to eliminate excess ethanol and gas residue. The last step is to make sure the fuel bowl is drained. Once this is done you can safely store the weed eater for winter.