Brake Fluid in Gas Tank—Are There any Consequence?

If you drive a car with a hydraulic braking system, you are using brake fluid. Brake fluid, also called hydraulic fluid, helps transfer the force exerted from pressing the gas pedal to the brakes. While this fluid is helpful in the braking system, it must remain in its compartment and work from there.

However, there have been cases of car owners mistakenly putting brake fluid in gas tanks. In some cases, it could be done by mischievous persons to punish a vehicle owner. But however it got there, it’s not healthy for your car. So what exactly happens when you put brake fluid in gas tank?

will brake fluid damage an engine

What will happen if I put brake fluid accidentally in the gas tank?

From my experience, the following are likely to occur if you accidentally pour brake fluid into gas tank.

Contamination of gas in the gas tank

Putting brake fluid in gas tank will contaminate the fuel in the gas tank. Thus, your fuel system will also get contaminated since the fuel travels through them to perform its function. The higher the amount of brake fluid, the more contaminated the fuel system becomes.

Fouling of the oxygen sensors

If you use silicon-based brake fluids, the oxygen sensors will malfunction if such polluted gas vapor reaches them. Oxygen sensors help measure the amount of air present in the exhaust and, in turn, send this information to your car’s computer. With this information, the computer can adjust the air-fuel ratio in the combustion chamber for proper combustion.

If, however, these sensors continuously get fouled by the hydraulic fluid for long, they will malfunction and send wrong information to the car’s computer. This could lead to a rich or lean fuel mixture in the combustion chamber which may eventually result in engine stalling, misfire, high fuel consumption, etc.

This implies that putting brake fluid in a gas tank won’t only cost you replacing the sensors, but it will also result in drivability issues since the engine’s performance will be compromised. The longer this goes on, the more likely your engine packing up.

Nothing may happen if a small drop of brake fluid is added

If there is a sufficient amount of fuel in the gas tank and only a tiny amount of the hydraulic fluid goes in, you have nothing to worry about. The fluid will dilute itself. When one of my trainees accidentally poured brake fluid into my gas tank, all I did was add more fuel which prompted the dilution of the fluid, and I was good to go.

However, I was observant to notice on time that what he was holding was brake fluid I flushed into a gallon and not gas. So only a tiny amount went in. If, however, you pour in a substantial amount, like a gallon, it will not dissolve in the gas tank. In this case, you will need to flush the gas tank immediately and put in new gasoline. If not, you risk damaging your engine.

Note this: Most times, having up to a gallon of brake fluid or more in the fuel tank is most likely a naughty act. It’s almost impossible for any car owner to mistakenly pour a gallon or more of hydraulic fluid into a fuel tank without noticing. So how do you know when someone pours brake fluid into the gas tank?

The presence of brake fluid or other foreign bodies in the gas tank may result in engine stalling, misfires, higher emission of white smoke, poor fuel economy, etc. Should you notice these, quickly sniff the fuel in the gas tank and compare it with the fresh fuel in your gallon.

Just like anyone can put in brake fluid, they can also put urine, bleach, or even engine oil in gas tank. So even if you don’t perceive brake fluid, there are likely other substances that someone can dump into the gas tank to get at you. So if you’re asking, why is there oil in my gas tank? You now know one of the reasons.

Frequently Asked Questions – FAQs

Q: Will brake fluid mess up an engine?

If you are wondering, will brake fluid damage your engine? It depends. Whether brake fluid will mess up an engine depends on where you put it. If in its reservoir, it will work fine in the braking system to transmit the power needed to stop your car. However, brake fluid can mess up your engine if it enters the gas tank in large quantities.

It will mix with the fuel running through your engine and limit engine performance. It may even hurt your catalytic converter, resulting in the release of toxic gases into the atmosphere.

Q: What does brake fluid do to an engine?

Brake fluid helps transfer brake pedal force to the brake pads, which helps to stop your wheels. It also serves as a lubricant and has anti-rust properties that enable proper performance and extended life span of the braking system.

If, however, it goes into the wrong place, it can foul the fuel system and oxygen sensors, which eventually leads to drivability problems. And if you unconsciously put brake fluid in the engine directly, it will break down seals and even cause accelerated component wear.

Q: Can brake fluid damage your car?

Aside from the gas tank and engine, there are other places brake fluid can meet in your car. For example, the body of your car. Brake fluid contains glycol, a very abrasive compound that can eat up your car’s exterior paint within 5-30 minutes. Cars coated with low-quality paint or without wax protection will likely get damaged in less than 5 minutes.

From experience, cars with quality paints and those newly waxed only needs to be wiped and washed with only water to prevent damage. Cars with low-quality paints need instant cleaning, washing, and proper rinsing to prevent the fluids’ corrosive effects. But if the fluid has already left visible marks, contact a professional to help out before it spreads further and causes more rust.

Q: Does brake fluid and petrol mix?

Brake fluid and petrol are similar products and are miscible. Like petrol, brake fluid has a lot of molecule alcohol in it and can dissolve in gasoline and vice versa. Please note that while any amount of brake fluid will mix up with gasoline, not every quantity of brake fluid will dissolve in gasoline.

To dissolve means gasoline has sucked it up, and the system won’t recognize the presence of brake fluid in gasoline. Note that only small brake fluid in gas tank will dissolve in gasoline.

Q: How do you clean brake fluid off an engine?

If you accidentally spilled brake fluid in your engine bay, you can clean it by rinsing or flushing it with water. Brake fluid is soluble as water, so it would quickly go off. More importantly, do this immediately, as brake fluid will start eating up the car paint immediately.

High-pressure water or a spray bottle can come in handy. You can also fill a jug with water and pour it on the engine bay; do this twice for a more effective result. If it still looks greasy or has been left for more extended periods, clean it further with a degreaser or warm soapy water.

Q: What not to put in a fuel tank

Do not put anything in your fuel tank aside from gasoline. If at all you need to, only use what is recommended by your experts, like the lacquer thinner. That said, do not put excess oil, bleach, wrong fuel, sugar, hydrogen peroxide, water, urine, or even transmission fluid in gas tank, as they can ruin your engine. However, some are worse than others.

The worst thing to put in gas tank is bleach because it doesn’t take long to act. But how much bleach in gas tank can ruin your car? Even a tiny amount of bleach will damage your engine, especially if you have very little fuel in the gas tank.

Final Thoughts

Putting brake fluid in gas tank has the short-term effect of tainting your oxygen sensors and fuel system, especially when in large amounts. Should this continue for long, the fouling of the oxygen sensors may cause a reduction in engine performance and damage other components like the catalytic converter.

If only a tiny quantity enters, top it with gasoline immediately. So long there is sufficient fuel, it will dissolve, and your engine will run fine.  If, however, a large quantity goes in, quickly drain your fuel tank and pour in fresh gasoline. If you’ve driven the car, you may need to flush your fuel system and change the fuel filter.

Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

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