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It can be hard for me to throw away an old container of two-stroke oil. I get that from my dad. He grew up during the depression and as a result, he never threw anything away. From his perspective, nothing ever went bad. Not oil, not gas, not bread (well, maybe bread – but stale was still edible).
So, does 2 cycle oil go bad? Yes, 2 cycle oil can go bad. If sealed, two-stroke oil usually good for up to 5 years. If opened, the shelf life is reduced to 2 years. Once mixed with gas the fuel should be used within two months.
Before preparing the gasoline-oil mixture, ensure that the oil has not been exposed to:
- Extreme heat
- Drastic temperature change
- Water or moisture damage
Any of these can spoil the quality of the oil and damage a 2-stroke engine.
The rest of this article will discuss the factors that cause 2 cycle oil to go bad. And don’t miss out on the tips to prepare the perfect gasoline and 2-cycle oil mixture for your equipment!
Two-Stroke Oil Lifespan
Two-stroke oil, (also known as two-cycle and 2T) are engine oils specially designed to create a viscose mix with gasoline. These oils blend with the gas in the tank and, once fed to the crankcase, keep the crankshaft lubricated.
If you are using only fuel in a 2-stroke engine, it can result in the failure of the engine. Two-stroke oil must be mixed with it.
Popular 2-stroke oil brands include:
- Red Line
- Briggs & Stratton
Each manufacturer might state a specific shelf life on the container. As a general rule, though, you should swap the oil for a new one if:
- It is in a sealed container, but older than 5 years
- The bottle is open, and the oil is older than 2 years
- The container holds a mixture of gasoline and oil that you have prepared longer than two months ago.
Alongside these estimated shelf lives, you should take into consideration the quality of the oil before mixing it with the gasoline. This is super important if you are dealing with a previously opened container.
You should consider replacing the oil if it has been subjected to:
- Rapid changes in temperatures
- Extreme heat
- Water damage
- The container has been left open without a lid
All these conditions can lower the quality of the oil, reducing its viscosity and lubrication power. Remember, a 2-cycle engine will fail if it does not receive sufficient oil lubricant.
Lastly, when preparing the mixture, do not use a gasoline type that contains more than 10% alcohol (usually labeled as Ethanol). Alcohol will attract moisture over time.
A mix of gasoline and oil that absorbs more than 1 ounce of water will separate. As a consequence, a spoiled blend can damage your carburetor.
Be sure to read my in-depth review of Ethanol And The Growing Issue Of Small Engine Problems.
How To Pick The Best Two-Stroke Oil For Your Equipment
When buying the oil for your machine, there are few features that you should factor in to preserve the functioning of the two-stroke engine. Here is what to look out for:
Level Of Residues
Unlike four-stroke engines, two-cycle engines run on a mixture of oil and gasoline, which means that the oil will enter the crankshaft directly. During the combustion process, the oil is completely burned alongside the gas.
If the oil tends to leave behind residues as it burns, these will deposit inside the crankcase and on the spark plug. In both cases, this will lead to a failure of the spark plug. If this happens, you will need to clean or replace the spark plug altogether. It can also cause significant engine damage over time.
Level Of Ash
Commercial lubricants often include additives, detergents, and minerals, in their list of ingredients. Among these, you can find particles of zinc, calcium, and molybdenum, which are anti-wear materials essential for the oil to function efficiently.
However, one of the main disadvantages of these compounds is that they leave deposits, or ash, behind. Ashless lubricants have a limited ash content of just 0.01%, which allows them to prevent the clogging and poisoning of the system (source).
Types Of 2-Cycle Oils
There are four different types of 2-stroke oils on the market today:
- Castor Oil
- Mineral Oil
- Synthetic Oil
- Semi-Synthetic Oil
Depending on the one you pick, you will experience different viscosity and shelf life. However, if there is already a mixture in the tank of your equipment, you should avoid adding a new mixture prepared with a different kind of oil.
Also called vegetable oil, these oils are plant-based and sometimes food graded. Their viscosity and lubrication level are high. Studies have shown that castor oil tends to produce lower quantities of smoke and pollution but creates ash and residues that can result in engine problems (source).
Also called petroleum oils, such oils are derived from oil reserves. After sourcing, mineral oils will go through a cleaning and filtering process. These lubricants used to be among the most common oils for two-stroke engines (source).
However, more modern equipment today requires a lower level of smoke and does not need as high levels of viscosity as the ones contained in mineral oil.
Most modern two-stroke engines run best on synthetic oils (source). These oils are the most advanced lubricants on the market. They offer not only great levels of viscosity, but they also lower the emissions of your equipment while regulating smoke production.
The last category of oils that you can find on the market is semi-synthetic oils. These are a blend between the incredibly modern synthetic oils and high-quality minerals. These benefit from the qualities of the two parts.
I tend to favor synthetic and the majority of premixed fuels on the market utilize synthetic oil in their mixtures (see my comparison of premixed fuels).
What Is The Perfect Gasoline-Oil Mixture For My Equipment?
I left the DIY homemade premix crowd a couple of years ago and moved to commercially-prepared premix fuels. But the gasoline-oil mixture, or homemade premix, can be done in a few simple steps.
- Age of your equipment
- Quality and type of oil you are using for the blend
The gasoline-oil ratio can vary depending on the age of your machine:
- For machinery manufactured before 2002, the correct gasoline-to-oil rate is usually 32:1
- For machinery built after 2002, the correct gasoline-to-oil rate is 40:1
- If you are not sure how old your equipment is, be aware that just about all handheld machinery with a 2-stroke engine can run on a 40:1 rate, though 50:1 is becoming more common.
In terms of calculating how much oils you should mix with the gasoline, follow these guidelines:
- For a 32:1 ratio, mix 1 liter of gas with 31.25 ml of oil
- For a 40:1 ratio, mix 1 liter of gas with 25 ml of oil
- For a 50:1 ratio, mix 1 liter of gas with 20 ml of oil
Steps To The Perfect Homemade Premix Fuel
To create the ideal premix for your 2-stroke engine, you should:
- Pour the oil first. Add the oil to an empty gas can.
- Add the gasoline into the can. Do not shake or stir.
- If you are storing the mixture for 30 days, add a stabilizer to the gasoline before pouring it on the oil.
- Label the mixture and include the date it was mixed
Consider A Commercially-Prepared Premix Fuel For Optimal Results
As I said before, I stopped mixing homemade premix fuel a long time ago. Buying commercial premix gives you precise gas-to-oil ratios, premium ingredients, and longer shelf life. It may feel like you are paying more but read Why Is Premixed Fuel So Expensive? to really understand the cost-vs-benefit to your equipment.
Now you should know whether you can still use the oil that you have been storing for a few months. While it takes a while for 2 stroke oil to reach its expiry date and not be usable, the factors I’ve outlined can influence that date and accelerate spoilage.
An open container of 2-stroke oil is usually fine to use for up to 2 years. Alternatively, a sealed container will preserve the quality of the oil for up to 5 years.
And if you are just sick and tired of dealing with gas, oil, and small engine repair, be sure to read Gas vs Electric: 6 Reasons To Use Battery-Powered Yard Tools