What Happens If I Fill My Motorcycle With The Wrong Gas?

Panic begins to set in as you finish fueling up your bike and realize you used regular fuel instead of premium. The fuel cap clearly says “unleaded premium fuel only” but you were too busy daydreaming about pulling a massive wheelie out of the parking lot to focus on pushing the correct fuel button on the pump.

Now the question becomes how much damage have I done and do I need to tow my bike, or do I just send it and hope I don’t throw a rod on the way home.

Motorcycles that are consistently filled with the incorrect type of gas may develop significant internal engine issues due to pre-detonation of the air-fuel mixture in the combustion chamber. This depends on the type of engine and fuel that was incorrectly used.

What Is The Difference Between Premium, Mid-Grade, And Regular Gas

The different grades of gasoline at the pump are differentiated by numerical octane ratings. These octane options may range from as low as 87 for regular up to typically 91 for premium, but sometimes as high as 94 can be offered at some select gas stations.

If you are near a racetrack, sometimes 100+ octane fuel is offered. This is because racecars typically have higher compression engines which require higher octane fuel (we’ll dive more into this later).

Most gas stations will offer three options of gasoline to accommodate most passenger vehicles. Lower compression engines found in commuter vehicles will have no problem using lower-grade fuel.

Different grades of fuel are separated by cost. Higher grade, higher cost. See the table below for the national average cost trend for each grade as of May 2022.

Regular
(87 Octane)
Mid
(89 Octane)
Premium
(91 Octane)
DieselE85 – Ethanol
Present Day Average $/Gallon$4.57$4.91$5.20$5.58$3.92
Last Month Average $/Gallon$4.09$4.49$4.77$5.03$3.54
Last Year Average $/Gallon$3.04$3.38$3.65$3.17$2.55
It’s irrelevant to this article but interesting to note the change in gas prices due to the events between May 2021 and May 2022.

What Do The Different Octane Numbers Mean?

The number that defines the octane rating determines the volatility of the gas, or put another way, how resistant the air-fuel ratio is to detonation inside the combustion chamber.

You will only see these ratings on gasoline pumps because the octane ratings don’t apply to other fuels like diesel.

The ratings read left to right on the pump in order of lower to higher octane.

A diesel fuel filler handle is typically the color green to separate it from the other fillers to avoid mistaking diesel for gas.

The higher the octane number, the more pressure the mixture can be under without detonating.

The reason why this number is so important is that it must be matched with the compression of the engine in order for the engine to operate properly.

What Damage Can Using The Wrong Gas Cause?

The problem with using low octane gas in a high compression engine is that pre-detonation may occur. The gas mixture detonates so easily that it might happen at the wrong moment of the engine cycle.

Engine timing is critical to proper function. The timing chain or belt in your motorcycle is precisely adjusted to make sure that detonation occurs at the correct point in the engine cycle.

The wrong octane fuel can cause that moment to occur too early which will cause engine damage over time.

It’s important to note that making the mistake of using the wrong gas once or twice most likely won’t send you to a repair facility. The repeated use of incorrect gas is what can cause some serious problems.

Is It OK To Mix Different Grades Of Gas?

There are some common misconceptions surrounding the topic of mixing different grades of gasoline.

As a general rule, mid-grade fuel is simply equal parts regular and premium gas mixed together. Therefore, it is safe to use mixed fuel in your motorcycle unless it specifically calls for premium high octane fuel.

It is not necessarily a different type of fuel, but simply a middle ground between high and low octane fuel.

Therefore, if you decide to mix different grades of gas, you will just end up with an end result somewhere between the higher and lower grades used.

It doesn’t make much sense at all to dispense 87 and 91 octane fuel into two separate containers and mix them equally into your bike as this has already been done for you.

Likewise, if you mix low and mid-grade or mid and premium, there isn’t much to worry about as you have minimally changed the octane rating and mostly just wasted your time.

Should I Use A Fuel Additive?

Fuel additives serve a few different purposes and are quite effective if used properly.

Two of the more commonly used fuel additives are an octane booster and a stabilizer.

Octane Booster

The name defines the product in this instance. An octane booster is used to increase the octane of the fuel currently in your tank. They work by raising the concentration of gasoline that is available to burn.

The idea here is that if you accidentally filled your high-performance motorcycle with low octane fuel, you can add a solution that will increase the octane to safe levels for your high compression engine.

Check out this link for an octane booster I have used in the past and had good success using with no damage to my engine.

Fuel Stabilizer

Stabilizer serves an entirely different purpose. This is for folks who let their bike sit for extended periods of time.

The function of a fuel stabilizer is to hold the gasoline solution together inside your fuel tank over time and prevent separation.

Over time, fuel separates and leaves the heavier water at the bottom of the tank. All gasoline, unfortunately, is comprised of a certain percentage of water by nature. Water is heavier so it sinks, and as a result, if the motorcycle is started after a long time of sitting, the engine will suck a big gulp of water right off the bat.

This is an undesirable result and can also cause engine damage.

I personally pour this fuel stabilizer into the fuel tank of any bike I expect to sit longer than a month or so. Click the link to see the product details.

When Should Fuel Be Emptied From A Fuel Tank?

As a general rule, any foreign fuel that would do damage to your engine should be removed from your fuel tank.

In the event that you have used a foreign substance that you don’t feel comfortable running through your engine, draining the tank might be the best option if you want to reduce risk.

  • One instance where this would be applicable would be if the fuel is so old that it has degraded and lost its combustibility. This stale gas will enter the engine but not start the bike but just clog up the internal passages and cause more trouble. You can identify old fuel by the smell: typically something along the lines of paint thinner.
  • Another time you should drain your tank is if you fill it with diesel fuel. Diesel fuel doesn’t ignite, so if it enters your engine designed for gasoline it will only cause issues.

It is very bad to run diesel fuel through a gas engine. Diesel fuel is denser than gasoline, so the thicker solution will clog up your injectors and put added strain on your fuel pump.

How To Remove Gas From A Motorcycle Gas Tank

If you come across one of these circumstances where you need to empty the fuel from your tank, there are a couple of simple methods from which you can choose. I have personally performed two of these methods and don’t currently have a favorite because emptying a fuel tank is annoying in general.

  • Siphoning Gas From A Motorcycle

I would argue this is the easiest method if you have the tools available. All you really need is a hose, a bucket, and your mouth, but I would insist you splurge and go for a pump as well. The idea here is to get the gas up and out of the tank and flow down the tube through a vacuum force.

This is why if you suck on one end of the line with the other end in the tank of fuel, gas will start to draw down toward you. The trick is to get your mouth out of the way before the fuel gets to you.

Use any means necessary to generate a vacuum force to get the fuel out of the tank and into your secondary reservoir. Get as much fuel out as possible then add new good gas.

Don’t sweat getting every drop out of the fuel tank. Once new fuel is added to your nearly empty tank, the concentration of good to bad fuel will be great enough to do no damage to the engine.

  • Removing The Tank On A Motorcycle

If you have a simple set of tools on hand, this is the ideal choice in my opinion. Motorcycle fuel tanks are typically held down by two bolts upfront by the triple clamp and a hinge bolt near the front of the seat. In most instances, the seat will need to be removed to access this second bolt.

Once unbolted, the fuel lines running from the tank to the engine will be the last thing in your way. In most instances, when you remove the fuel lines, you will be able to block off the nipples (one for feed and one for return) with a rubber cap. Otherwise, gas will start to spill all over the place. You might have to get creative at this point if your bike has a different style fuel system.

After those two steps, you can now take the tank and flip it upside down so the fuel pours out of the gas cap into your secondary reservoir. Perform steps above in opposite order to reassemble.

  • Flipping The Motorcycle Upside Down

I included this third option for humor and also because I have seen it done successfully once before. If you’re in a desperate situation, don’t have any tools, but do have a set of ratchet straps and a mounting point on the ceiling that will hold the weight of your bike, you can certainly invert your bike in a semi-stable fashion.

Using Ethanol Fuel In A Motorcycle

All gasoline options available at gas stations will contain some percentage of ethanol. Some gas stations, however, will offer an option with a much higher percentage of ethanol that is typically cheaper.

As a general rule, gasoline with high levels of ethanol are ok to use in 4-stroke motorcycle engines because the oil does not mix with the gasoline.

The problem with high ethanol content fuels is that they will break down oil if they come in direct contact. Because the fuel and oil are kept separate in the traditional street bike, this won’t pose an issue.

However, I wouldn’t recommend the consistent use of high ethanol content fuels. The ethanol itself is defined as hygroscopic meaning it absorbs water from the air. The issue with this, especially in a small engine, is the fuel blend will separate.

Having water inside the engine is extremely bad as it will cause excessive corrosion inside the engine and fuel system leading to catastrophic failure.

Summary Of Motorcycle Fuel Options

We have discussed many nuances of gassing up your bike. Here’s a quick wrap up to help you make a decision if you’re unsure if you made a mistake.

  • Regular fuel with low octane should be avoided in most instances when filling up your motorcycle
  • Higher octane premium fuel will not damage your motorcycle engine
  • Avoid alternative fuels like diesel and E85 ethanol

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