Small Engine Gasoline Guide
The best fuel type and octane rating for small engines
I'm a man who likes quality, but spending more money for something doesn't always mean it's better.
When you fill up your car at the gas station, there are usually three different types, or grades of gasoline to choose from. Often, youíll see Unleaded, Midgrade, and Premium. Each will have a number, typically ranging from 87-92.
If youíre unfamiliar with what these octane ratings mean, you might pay extra for premium gas, thinking it ďsoundsĒ better. The same goes for filling up your lawn mower, snow blower, or other gasoline-powered equipment. Maybe you think youíll get better efficiency, but thatís largely a myth unless your manual specifically calls for it.†
In this article, we'll talk about everything you need to know about gas and your small engine.†
What is an Octane Rating?
In order to understand octane or anti-knock ratings, you should understand the basics of how an engine works.
Letís use a 4-stroke engine to illustrate:
- The Intake stage (piston moves down) draws in air and fuel into the engineís cylinder.
- In the Compression stage (piston moves up), the engineís piston compresses the air/fuel mixture.
- In the Power stage, the spark plug ignites the air/fuel mixture, creating an explosion that forces the piston downward, (which drives the machine to work).
- In the Exhaust stage, the piston comes back up to force exhaust gases out.
In a 2-stroke engine, these steps still occur but are streamlined into two strokes (the piston goes up once and down once).
If we look at the compression stage specifically, then we can see how octane affects performance.
Today, manufacturers are increasingly building car engines with high compression ratios (previously found mostly in the racing world), which means the air/fuel mixture is put under more pressure and is more explosive.
Higher compression translates into more efficient use of air and fuel, but it makes the mixture burn much hotter than lower compression. This can cause the air/fuel mixture to spontaneously combust (without a spark) in a phenomenon known as knocking, or pre-detonation.
Knocking can occur before the piston reaches the top of the cylinder, forcing it down prematurely, thereby wrecking the engineís timing and inflicting serious damage.
High octane gasoline is specially refined for higher compression engines to prevent knocking. With a higher octane, the air/fuel mixture can endure higher compression without combusting. Thus, octane is the measurement of a fuelís resistance to knock and is on a scale of 1-100.
What Octane Rating Should I Use?
For those wondering ďIs premium gas better for small engines?Ē the answer is most likely no. Thatís because small engines are not built with high compression ratios. There is no threat of engine knock taking place. †
Sure, you wonít hurt your lawn mower or string trimmer by putting in Premium gasoline, but youíll be wasting your money since itís more expensive. Contrary to popular belief, Premium gas does not improve fuel efficiency or performance†in motors that don't require it.†
Certain gasoline suppliers claim that their Premium fuel is cleaner and better for the engine, and people like my cousin swear by it. However, these claims are largely untested. If you perform regular maintenance on your equipment, (keep fresh fuel, clean the carburetor, etc.), then Regular octane gas will work just fine.†
You only need Mid-grade or Premium gas (89-octane or higher) if you have a vehicle†with a high compression ratio, which will be noted in your ownerís manual. In that case, using regular gas could cause knocking and damage the engine.†
What is the Best Gas for Small Engines?
If octane doesnít really matter for small engines, then what does? There are a couple of considerations to make when choosing gas:
Buy Fresh Fuel
By far, the most crucial step is to use fresh fuel. New gas is critical for a small engine to operate properly. There are many gas station companies out there. Choose one that does its own refining (typically name-brand stations)óthat way the fuel will be as fresh as possible.††
Buy Quality Fuel
As I said, more expensive isn't always the best, but don't go for the cheapest of brands out there either. I recommend going with a Top-Tier fuel, which contains extra detergents that help prevent gum buildup and carbon deposits in the engine's critical parts and maintain performance.†
Once you buy the fresh fuel, store it in a plastic gas can, and add fuel stabilizer to keep it fresh. A good tip is to only buy a 30-day supply of fuel at a time and run the carburetor dry if you won't be using it for a while. That way youíll use what you bought and not leave fuel stagnating once the season ends.
You might hear about ethanol, a corn-based fuel, in the news, and itís becoming more and more popular thanks to its clean burning properties. Ethanol is mixed with gasoline in a proportion, typically 10 or 15 percent. You may have heard of E85, which contains 85% ethanol.
Despite its rising popularity, ethanol is a poor choice for small gas engines. Ethanol attracts moisture from the air, separates from the gas, and sinks to the bottom of your engineís fuel tank. This watered-down ethanol is then fed into your engine and can cause ignition problems. Ethanol is also corrosive and burns really hot, which can cause overheating and irreparable damage.†
Itís best to use ethanol-free gas in small engines. If you do decide to use ethanol, donít use a fuel that is more than 10% ethanol (E10), and be sure to add fuel treatment to prevent the fuel from separating.
Donít overthink fueling your small gas engine. As long as you have fresh fuel, use a stabilizer, and avoid ethanol, youíll get peak performance out of your machine.
Now that you also understand octane, you know itís not necessary to waste money on Premium or Midgrade gas unless you have a high compression engine or your owner's manual specifies it.
Using Regular gas in well-maintained equipment will keep your lawn trim in the summer and the driveway clear of snow during winter. Quality without the price tag--that's something I can go for!