What To Do If You Put The Wrong Octane Gas In Your Rental Car

Wrong gas in car

What happens if you put the wrong gas in car?

I see this question a lot in auto forums. Someone fills with 87 octane in an engine that requires 93. Then they realize the problem and want to know what will happen if they put the wrong gas in car.

Modern cars and compensate for the wrong gas

Car computers can’t tell what gas you put in your tank. It can only determine how well the gas is performing in your engine. If you have a high performance high compression engine and you fill with low 87 octane gas, the computer will detect the difference by way of the knock sensor. As it detects knock signals caused by detonation (gas ignites from the heat of compression instead of from the spark plug), it retards ignition timing to avoid the double ignition–one from the heat of compression and the second from the spark.

But the computer can only compensate so much. Once the computer retards spark timing by a certain amount, if it still detects knock, it will set a trouble code and turn on your check engine light.

What to do if you used wrong gas in your car?

Nothing. Drive less aggressively because pedal to the metal driving will cause more knock events. Your goal is to prevent knock by gentle driving, use up at least a 1/4 tank as quickly as possible and refill with a higher octane fuel. Keep doing that and you’ll be fine.  You don’t have to add octane booster to correct this problem.

Will the check engine light go out on its own?

If the trouble code appeared shortly after you added the wrong gas to your car and you’ve since filled with the right gas, the computer will gradually adjust and the light will go out.

Gasoline in a diesel gas tank

However, if you put gasoline in a diesel powered car, the engine will detect this almost immediately and refuse to power up. This can lead to significant damage to the engine components which might require you to get an entirely new engine. The damage is very pronounced because gasoline is more combustible which causes knocking of the engine

When you notice that you have put the wrong gas in your vehicle, it is advisable that you shut it off at once. You should then ask your mechanic to come and help you to drain all the gas from the gas tank and fuel lines. You can do this process on your own but it is better to have a professional help you so to ensure that all the gas has been drained and avoid any further damage. If you continue to use your car after you believe that you have put in the wrong gas, you’ve been warned. We recommend that you don’t do this as you will cause great damage to your beloved machine.


Can you put mixed gas in the car?

It is not advisable that you use mixed gas in a car. Commonsense dictates that if you try to run an electronic with the wrong type of gas there will be some damages that you are definitely not ready to pay for.

You can, however, use mixed gas in a vehicle and not experience any engine damage. This applies only if the amount of mixed gas you have used is substantially low and there is some gas in your tank that will dilute the mixed gas creating fuel that can be broken down by your engine to produce power. If you fill up your tank with mixed gas without the presence of the correct gas, chances are very high that you will experience engine failure and permanent damage of critical components.

Knowing the correct way to mix gas is the first step of protecting your engine. Before mixing the gas, ensure that you read the product manual to learn more about the specifics of the gas. Ensure that you use a gas that has high octane levels as low octane gas may lead to engine damage as it leads to overheating.

Before using mix gas on your car, ensure that the container used to mix the gas was of high quality. Storing mix gas in a substandard container may lead to spillage and permeation. It is also recommended that you use 2-cycle oils when creating mix gas. This because 2-cycle oils are specifically developed to give your engine enhanced protection and lubrication ensuring that it serves you for long.

Let’s Talk Octane

Octane Ratings

Regular, mid-level and premium are the three tiersRegular, mid-level and premium are the three tiers of gasoline available at most gas stations. Each grade comes with a different number that refers to the octane rating of the gas. The octane rating is a measurement of the fuels ability to resist knocking or pinging as the fuel is combusted in your car’s engine. Typically, the higher the octane rating, the higher the price.  Related: Which Gas Should I Use?

Using the Wrong Octane

Putting the wrong octane fuel into your car is a very common mistake. The fuel nozzles are all the same design and next to each other at the fuel pump. In addition to this, it can be tricky to know what the differences are between octane levels.

What Happens If You Put In Higher Octane Fuel Into An Engine That Doesn’t Need It?

There is a pervasive myth that using a higher-octane fuel is better for your car’s performance. Hint – it’s not. Typically, although there are some variations among engines, putting a higher-octane gas into your car than it requires will neither help nor hurt your car’s performance. There are some engines that are not designed to burn higher-octane fuel and you may see a reduction in power and fuel economy.

This mistake should not cause any major damage to your car – just be sure to pick the correct octane gasoline next time you fill up.

What Happens If You Put Lower Octane Fuel Into An Engine That Requires High-Octane Fuel?

Whether done by mistake or done to try to save on fuel costs – putting low octane fuel into an engine that requires a higher octane can cause problems that destroy your engine.

If you fill an engine designed to run on high-octane gas with a lower octane than recommended you will notice effects almost immediately. You will notice a poor engine performance. Depending on how long you have been using the lower octane fuel the erratic combustion produced from this error can cause over-heating and irreversible damage to your engine.

If you have filled your engine with a lower octane fuel than it requires then you should switch back to premium high-octane fuel as soon as possible. If you have been using lower octane fuel for an extended period of time it is best to get some diagnostics run by your mechanic to check for any lasting damage.

Related: What’s Wrong With My Fuel Pump?

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