Chainsaws, leaf blowers and other small 2-cycle engines need some oil in their gasoline to keep the motor lubricated and in running order. There are two main ways to go about this: mix motor oil into regular gas yourself or buy special pre-mixed fuel.
In this article, we are going to talk pre-mixed fuels: what is it and why should you use it. Shortly put, pre-mixed fuel is special ethanol-free gasoline with motor oil mixed in. Compared to regular gasoline, pre-mixed fuel stores better, keeps the engine cleaner and lowers the need for maintenance. The improved storage properties make pre-mixed fuel well worth the extra cost with occasionally used tools, but in intensive use the benefits must be weighed against the added cost.
Below, we will discuss all of this in more detail: what goes into pre-mixed, what are the benefits and what is it good for. We’ll also take a look at pre-mixed brands, where to get them, and I will also answer some of the most common questions on pre-mixed fuels. I will tell you why the more expensive pre-mixed may still be the smarter way to go.
What is pre-mixed fuel?
Pre-mixed fuel is simply gasoline with a small fraction of motor oil mixed in. This fuel mixture is intended for two-stroke engines, most of which need some oil in their gasoline for proper lubrication of the engine.
Pre-mixed fuels have their two components – gasoline and oil – in different mix ratios. The common mix ratios range from about 1:50 to 1:25, with 1:50 and 1:40 being the most common. A ratio of 1:50 means that one part of oil is mixed into 50 parts of gasoline.
Apart from the oil, most pre-mixed fuels differ from the regular gas in that they use a special gasoline in the blend. Practically all pre-mixed fuel is from ethanol-free gas; some brands even use a particularly pure gas called alkylate gasoline. These special gasolines give the pre-mixed fuels better running and storage properties than a self-made mixture of regular gas and engine oil would have.
Why is pre-mixed better?
Thanks to the special gasoline blend used, pre-mixed fuels improve engine performance, are more convenient to use and store better than most self-mixed fuels. Let’s break the advantages down:
1 Pre-mixed is ethanol-free
By contrast to most station gas these days, pre-mixed fuel is usually ethanol-free, i.e. it contains no ethanol.
Having no ethanol is important for small two-cycle engines that are in occasional or seasonal use because ethanol attracts moisture. Leaving ethanol-containing gas in the tank over the storage season leads to water accumulation which can cause a number of issues including corrosion, carburetor clogging and phase separation.
Another advantage of ethanol-free gasoline is that it is easier on the rubber and plastic components in the saw fuel line. While most new saws use ethanol-resistant parts, the fuel lines in many older saws may become brittle and crack if exposed to ethanol.
2 Pre-mixed stores better
Compared to regular gasoline, pre-mixed fuel has a longer useful life both in tank and on the shelf. This is mainly thanks to the gas in the pre-mixed being ethanol-free and not attracting water. Some pre-mixed fuels using special alkylate gasoline have improved stability in storage also thanks to the uniform composition.
Most pre-mixed fuel manufacturers quote many years shelf life unopened and at least 2 years opened, and allow for over-season storage in the tank. This relieves you from the hassle of draining your outdoor equipment from gas for the off-season.
3 Pre-mixed runs cleaner
Pre-mixed fuel burns more efficiently and controllably than a self-made mixture of regular gasoline and oil thanks to the purer composition of special gasoline used in these mixtures.
More specifically, the special gasoline blends used in pre-mixed fuel have higher octane numbers and are therefore less prone to knocking. They also have fewer heavy hydrocarbon components which are more difficult to burn completely and produce soot.
Thanks to the cleaner burning, a pre-mixed fuel gives you higher engine efficiency, less maintenance and longer engine life.
4 Pre-mixed is not corrosive
Pre-mixed fuel also saves you engine by being less corrosive than regular gasoline.
As many of the other benefits, the low corrosivity is mainly thanks to the lack of ethanol: no ethanol – less moisture, less corrosion.
Some pre-mixed fuels with alkylate gasoline are also free of fluorine – another corrosive agent in regular gas – and claim reduced corrosivity thanks to this.
5 Lower odor and emissions
Compared to regular gasoline, many pre-mixed fuels also promise lower odor and emissions, making them less hazardous for the user and environment.
This is thanks to the special gasoline used in pre-mixed fuel containing much less benzene, olefins and aromatics, all of which are volatile harmful carcinogenic substances.
Note that there is variation between brands here: not all pre-mixed fuel is made with alkylate gas and can claim the very low emissions.
Is pre-mixed worth it?
Pre-mixed fuel is considerably more expensive than regular gasoline: with prices of $6 to $8 for a standard 32 fl.oz. can, it costs between $20 and $30 per US gallon – that is ten times the price of gas at the meter.
|Price per gallon||3 $/gal||25 $/gal|
|Cost per tank||0.50 $/tank|
(20 fl.oz. / 600 cc)
(20 fl.oz. / 600 cc)
So are pre-mixed fuels like TruFuel and Aspen worth all this extra cost? The answer depends on your use profile and how much you value your time and your tool.
Light use: Yes
If you are running the tool non-professionally for a few days a year, paying for pre-mixed clearly makes sense: your gas bill is small anyway, and pre-mixed saves you time and gas – you can leave the gas in the saw for the next use. You also get the benefits of lower maintenance, less fumes and longer engine life.
Heavy use: Maybe
If, on the other hand, you are running a large, thirsty tool professionally all day every day, the pre-mixed cost may be significant. As an extreme case, a large chainsaw may run through 3 gallons of fuel during a working day of heavy logging. This makes around $70 with pre-mixed, but only around $10 with regular gas.
In everyday use, storage properties are a non-issue, and with pre-mixed you are paying for the lower maintenance, longer tool life and maybe cleaner exhaust. Whether you are willing to do this is up to you.
Best pre-mixed brands
Here is a list of some of the most popular pre-mixed fuel brands. All of them are ethanol-free and probably work great, but there are some differences in availability, package sizes and whether the gasoline is alkylate or contains stabilizers.
Aspen 2: Ethanol-free alkylate gasoline, 50:1 mix, 1 qt to 50 gal packages, very popular in Europe.
Husqvarna XP: Ethanol-free gasoline, 95 octane, 50:1 mix, 1 qt to 48 gal packages, good availability (Lowes, Walmart).
Stihl MotoMix: Ethanol-free, high-octane alkylate gasoline, 50:1 mix. Availability seems restricted to local Stihl retailers. Found no detailed info on composition.
TruFuel: Ethanol-free, high-octane gasoline, 50:1 and 40:1 mixes, 32 fl.oz. to 4.75 gal packages. Excellent availability (most major chains). Contains stabilizers.
Where to get pre-mixed fuel?
While pre-mixed fuel is not quite as ubiquitous as the regular gasoline you get from all stations, it is still quite easy to find.
Pre-mixed fuel is available in cans in most hardware stores, home centers, and also at many gasoline stations. I have listed the pre-mixed brands available at Home Depot, Lowes and Walmart in the table below.
Pre-mixed fuel is good for all two-cycle engines which use a fuel+oil mixture for lubrication.
Equipment with such a 2-cycle engine include the vast majority of chainsaws, leaf blowers, ice augers, weed eaters. Many older motorcycles and lawnmowers would also fall into this category and run well with pre-mixed fuel.
Pre-mixed fuel should not be used with:
- 2-cycle engines with auto-lubrication (scooters, some motorcycles)
- 4-cycle engines: cars, some snow mobiles, most motorcycles
NB: Many types of equipment can come with either a 2-cycle or a 4-cycle engine. Please make sure whether you are dealing with a 2-cycle, a 2-cycle auto-lube or a 4-cycle engine before refueling – choosing the wrong fuel type is likely to lead to engine damage!
How long does pre-mixed last?
Pre-mixed fuel lasts much longer in storage than regular gasoline thanks to the lack of ethanol, purer composition and sometimes the use of stabilizers.
Typical manufacturer-specified shelf lives for pre-mixed fuels are 2–5 years unopened, 2 years opened and about 6 months in the tank.
These storage times give you two practical benefits:
- You do not have to drain the tool tank from fuel between uses
- You will rarely waste an opened can due to water absorption and phase separation
Q & A
Let’s still address of a few of the other common questions on pre-mixed fuel:
Does pre-mix fuel go bad?
Yes – premixed fuel will eventually go bad too, although it stays good for much longer than regular gasoline. In an sealed can, most pre-mixed fuels should hold for at least 5 years, but only two years is typically given for an opened can.
Manufacturers do not specify what makes the pre-mix go bad, but it is probably the same processes as with regular gasoline: water absorption and phase separation.
Why is pre-mixed fuel so expensive?
Pre-mixed fuel is more expensive than regular gasoline because the gasoline it contains is a special high-purity blend which requires a more expensive production process.
With alkylate-type pre-mixed gasolines (Aspen, Stihl Motomix), the purity is reached with a process called alkylation.
Can you use pre-mixed in your car?
Your car engine is not intended to run on pre-mixed fuel (TruFuel etc.) and its use is not recommended.
Modern cars have 4-cycle (four-stroke) engines which are designed to be lubricated with a separate oiling system. These engines do not need or benefit from additional oil in the fuel – in fact, oil in the fuel is likely to do more harm than good.
While many car engines (older ones) may run just fine with small amounts of pre-mixed fuel blended into regular gasoline, pre-mixed fuel may in some cases do some actual damage to fuel injection systems and catalytic converters in newer vehicles.
Can you use pre-mixed in 4-stroke?
Four-stroke engines are not intended to run on pre-mixed fuel and its use in these engines should be avoided – see the above question on cars.
Is TruFuel really worth it?
TruFuel is similar to other pre-mixed fuels and ethanol-free, giving you all the benefits discussed above. If you value the better storing and lower maintenance, TruFuel is clearly worth it.