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Unveiling the Truth: Does Diesel Float on Gas?

Accidentally Added Gasoline To Our Diesel Tank

In a moment of haste at Turtle Bay, our crew mistakenly filled our diesel tank with gasoline. Initially, we didn’t notice the switch; the yellow jerry cans we handed to the Pangas were clearly labeled DIESEL, yet somehow, gasoline made its way into our 46-gallon tank. Anchored in Cabo San Lucas, we discovered the error only after the engine started showing problems.

Having about 20 gallons of diesel already in the tank, our immediate solution was to dilute the gasoline with more diesel. We grabbed our dinghy and headed to the fuel dock to fill up our cans. This isn’t the first time I’ve encountered such a mix-up. Once, a fellow sailor in a marina had to empty his entire tank and seek a fuel polisher to remedy a similar situation.

Strategy for Managing Mixed Fuel

From my experience, diluting the fuel is a practical approach, especially when you’re far from professional help. I’ve learned that older diesels, particularly in trucks, can run with a small amount of gasoline mixed in; it’s almost a standard practice to intentionally add a bit to tackle gelling issues in colder temperatures. However, newer common rail engines might not be as forgiving.

One must consider the risk to the injector pump and nozzles. These parts are critical for the engine and can be damaged due to the cooling and lubrication properties of the fuel being compromised by gasoline. Such damage could lead to costly repairs or a complete engine rebuild. As a rule, if the mixture is more than a few percent, it’s safer to drain the tank and refill it with pure diesel. This may seem like a pain, but considering the damage that could occur, it’s a small price to pay for your engine’s longevity and your state of mind.

In this industry, whether it’s a boat, truck, or any diesel rig, one learns to expect the unexpected. Each tank of fuel comes with its own set of challenges and responsibilities. The key is to stay informed and prepared, always ready to adapt to the demands of the sea and the quirks of the fuel we depend on.

Will gasoline and diesel separate on their own?

When considering whether gasoline and diesel will separate on their own, it’s crucial to understand their fundamental nature. Both fuels are blends of hydrocarbon compounds derived from petroleum crude oil. Once mixed, they tend to remain combined and don’t separate naturally. This is akin to mixing milk with coffee; once combined, they don’t split into distinct layers. The only way to separate them is through a distillation process, which involves heating and condensing the vapors at specific temperatures. In a practical scenario, like at a petrol station, you might observe stains on the ground near the pumps where petrol has vaporised under the sun and evaporated more slowly than diesel, which is heavier. This mixture of fuels won’t separate easily and handling it is not unlike managing a bad soup – it’s a complex blend where aromatics from gas may leave over time, but the overall composition remains mixed. For older gas engines, using smaller quantities of this mix might not pose significant issues, but it’s generally not advisable for high-octane engines or fresh diesel engines.

Which is worse for the engine, putting diesel in a “petrol car” or petrol in a “diesel car”?

In the world of fuel mishaps, accidentally adding the wrong fuel to a vehicle is not uncommon. The question arises: which is worse, putting diesel in a petrol car or petrol in a diesel car? From my experience, both scenarios aren’t ideal, but putting petrol in a diesel engine tends to be more catastrophic. For instance, a friend once filled his Peugeot309 diesel with 20 litres of petrol at a garage. Realizing his mistake after checking the receipt, he called his mechanic for advice. The mechanic advised keeping the engine running under no circumstances should he stop it. After driving on the motorway and repeatedly adding diesel to reduce the dilution, the car survived without permanent harm, though it ran lumpy with up to 75% petrol. Contrastingly, diesel in a petrol car, like the 2.0 EFI MG Montego scenario, where the tank was filled with £20 of diesel and then topped up with petrol, resulted in less severe effects. The car coughed, farted, and blew smoke, but eventually recovered with no long-term problems after a thorough flush. The key takeaway is the difference in engine design makes diesel in a petrol engine somewhat more forgiving than the reverse, where the wrong fuel can cause severe engine damage.


Why do we use gasoline instead of diesel?

The preference for gasoline over diesel in many vehicles can be traced back to its origins and properties. Initially, gasoline was a by-product in the production of lamp petroleum or kerosene. Due to its volatile nature, it was deemed too dangerous for lamps as it could easily explode. This surplus gasoline was often dumped or sold as a medicine until car owners began to buy this fuel from pharmacists. The development of gasoline engines by innovators like Mr. Otto, who invented the gas engine, and Mr. Daimler, who converted it to a petrol engine for cars, cemented gasoline’s place in automotive history. On the other hand, Mr. Diesel’s engine, which was initially used in stationary applications and ships, came later in development. The Otto motor, already established, had thus earned its place as the preferred choice for personal vehicles, while diesel found its niche in heavy-duty and maritime applications.

Is it possible for a diesel engine to not be damaged after putting in a bit of petrol?

As a retired heavy equipment mechanic, I’ve had my fair share of experiences with diesel engines and the occasional mix-up with gas. The question of whether a diesel engine can survive after being fed petrol isn’t straightforward. Diesel engines are robust and can sometimes withstand small errors, like a small amount of petrol mixed in. In cold, even subzero temperatures, a bit of petrol can actually help a diesel engine start and warm up faster. However, the issue arises when gas is used in systems not designed for it. Diesel fuel systems typically have an injection pump that is lubricated by diesel fuel itself. Introducing petrol, which can absorb water, poses a risk. Diesels generally have water separators, but these aren’t foolproof. Even a few drops of water can ruin an injector, creating a bigger problem.

Some military vehicles use multi-fuel engines that can adjust the amount of fuel injected to compensate for different fuel viscosities, ranging from jet fuel (kerosene) to gear oil. But in practice, this flexibility isn’t as reliable as claimed. In my experience, older, simpler engines are more forgiving when it comes to the wrong fuel, so a bit of petrol in a diesel engine might not be catastrophic. However, it’s a gamble. If wrong fuels are consistently used – like putting diesel in a petrol lawn mower or vice versa – it can lead to severe damages, potentially requiring a new engine or a complete rebuild. So, while a diesel engine might survive a bit of petrol, it’s always best to avoid such a mix-up for the health of your engine.

Would a 50/50 blend of gasoline and diesel be able to operate in either type of engine?

A 50/50 blend of gasoline and diesel fuel in an engine is a tricky scenario. In my days as a mechanic, I’ve seen a diesel truck that the owner’s wife had filled with gasoline by mistake. Surprisingly, the truck still ran, but it suffered from spark knock and had very little power. When the tank is filled with such a mix, draining and refilling become necessary to avoid further problems. On another occasion, a neighbor used a 50/50 gas-diesel fuel mix in his 70-year-old gasoline-powered tractor to plow snow in his driveway. Although it worked, the tractor was noticeably underpowered, and the biggest problem was starting it in frigid cold without an engine heater. In theory, a 50/50 mix might seem feasible, but in practice, it leads to inefficiencies and potential damage. For instance, in a diesel engine, such a mix could lead to piston damage or worse, making it an impractical and risky choice for either type of engine.

Can we extract gasoline from diesel?

Extracting gasoline from diesel is a complex process that involves more than just physical separation. As Mr. Ward once explained, this extraction isn’t as simple as pouring one liquid from another. Instead, it requires a chemical reaction process. In a refinery, when diesel is fed into a hydrocracking unit, its longer carbon chains are broken down into gasoline-range material. This material, known as naphtha, is typically of low octane. To upgrade its octane level, it’s further processed in a catalytic reformer. The intricacy of this process reflects why an oil major I once knew, whose marketers would dictate the refinery operation, found it troublesome to sell diesel and buy back gasoline. They preferred to crack the diesel into gasoline, especially in winter when diesel was more valuable in the market. This company eventually merged with a competitor and no longer exists, but their approach to fuel processing highlights the complexities and economic considerations in the fuel industry.


Why aren’t gasoline and diesel fuel interchangeable?

The reason gasoline and diesel fuel aren’t interchangeable lies in their distinct chemical properties and the specific engine designs they cater to. Gasoline engines, operating on the Otto or Atkinson cycle, rely on spark ignition. This requires the fuel to form a uniform mixture of vapor molecules that a spark-ignited flame front can efficiently propagate through the air-fuel mixture. Gasoline’s volatile nature facilitates this process. Conversely, diesel-cycle engines work on compression-ignition. Here, the atmosphere in the cylinder is compressed until it’s hot enough to burn the diesel oil without any spark, eliminating the need for spark plugs. Diesel fuel, made up of longer-chain, denser diesel-range hydrocarbons, is less volatile and safer, yet packs more heat energy. These fundamental differences affect everything from combustion timing and injection methods in the engine to efficiency and compression ratio requirements. While diesel engines can handle higher compression ratios without risk of pre-detonation or knock, gasoline engines need a constant 1:14.7 fuel-air ratio, even under no load, making them unsuitable for multiple fuels. The disparate nature of these fuels and engines underscores why they cannot simply be swapped or mixed without risking significant damage to the engine system.

Litte bit of gas in the diesel container?

Imagine you find a diesel container that’s almost empty, but then you discover there’s a tiny amount of gasoline left in it – about a 1/2 ounce of gasoline 87 octane, to be precise. This scenario is more common than you might think. Perhaps a guy at a service station mixed up the diesel and gasoline cans, or maybe someone used the diesel cans for gas and vice versa. Either way, you’re left wondering: does this small amount of gasoline make any difference if it’s mixed into 5 gals of diesel?

From my experience with tractor trailers and discussions with old truckers, it’s known that drivers sometimes spike their tanks with a couple of gallons of gas for extra power, especially in older diesel engines. Modern diesel engines might not tolerate this practice as well. When gasoline is mixed into diesel fuel, it can float on top due to the difference in weight between the two. Diesel fuel is generally heavier than gasoline, so the gasoline will sit on top of the diesel in the tank. However, older diesel engines can sometimes handle up to a 30% mix of gasoline, which is deemed acceptable. This mixture can even help reduce gelling in cold weather.

But what about the engine’s health? Gasoline lacks the lubrication properties of diesel, which means that too much gasoline in a diesel engine can lead to the injector pump failing, as it relies on diesel for lubrication. In my experience, a small amount of gas in a diesel engine generally doesn’t cause significant problems, but it’s always best to avoid such mix-ups. A diesel engine can handle a little gasoline, but pushing its limits could lead to costly repairs down the line

Accidentally mixing gasoline and diesel fuel – What happens then?

When gasoline is accidentally mixed with diesel fuel in a diesel tank, the consequences can range from minor to severe, depending on various factors. I recall a situation at the Bell office where a customer called about his tractor’s diesel fuel tank being mistakenly filled with gasoline. In such cases, the mixing of fuel types is not advisable and can lead to a disaster. The primary issue stems from the gasoline diluting the diesel’s lubricity, potentially causing problems in the engine’s fuel system. Gasoline in a diesel engine can degrade the fuel’s quality, leading to inefficient combustion and possible damage to components. The factor to consider is the proportion of gasoline to diesel; a small amount may not be catastrophic but could still adversely affect engine performance. In summary, mixing gasoline and diesel is a risk one should avoid, and if it happens, the best course is to drain and clean the fuel system thoroughly to prevent potential engine damage.

Big Differences Between Gasoline And Diesel Fuel

Understanding the Big Differences between Gasoline and Diesel Fuel is crucial, especially when considering the potential for accidentally mixing them. At the Bell office, we’ve encountered scenarios where customers with tractors or vehicles with diesel fuel tanks mistakenly added gasoline. The problem arises due to the fundamental differences in the two fuels. Diesel is heavier, comprised of large molecules, and atomizes differently due to its density and viscosity. Its flash point and autoignition temperatures are also significantly higher compared to gasoline, which is lighter and vaporizes at a lower temperature. These physical properties play a vital role in how each fuel behaves in engines and fuel systems. Mixing gasoline in a diesel tank is not advisable as it can lead to a disaster, affecting the engine’s performance and potentially causing severe problems. In both on-road and off-road applications, using the correct #2 diesel fuel or gasoline as intended is a critical factor to expect smooth engine operation.

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Putting Gasoline In Diesel Fuel

Putting gasoline in diesel fuel can lead to several problems due to the difference in their chemical compositions. Even a small amount of gasoline can depress the flash point of diesel, making it more dangerous. This mixture creates pockets of higher concentrations of gasoline in the tank, leading to an inconsistent flash point. The flash point temperature of diesel is significantly altered, causing it to prematurely ignite in a diesel engine and potentially leading to engine damage. Furthermore, gasoline acts as a solvent while diesel is more of an oil. This distinction means that gasoline lacks the lubricity to properly lubricate the fuel pumps and injectors of a diesel engine, which can result in further damage. Additionally, incomplete combustion of this mixture in the engine can cause black smoke – more than just an aesthetic problem, it signifies a deeper issue. The vehicle’s computer system may try to compensate for this lack of combustion, adjusting the fuel-air mixture and leading to reduced power and performance. Continuous use of this contaminated fuel can cause damage to the vehicle’s computer sensors, potentially overheating them or covering them in soot, which impedes their ability to detect and regulate the engine’s functions properly.

Putting Diesel Into Gasoline

Putting Diesel into Gasoline engines, essentially the reverse of the usual mistake, presents its own set of issues. Diesel, being a heavier fuel with a higher flash point, contrasts sharply with gasoline, which is lighter, more volatile, and burns at a much lower flash temperature. This diesel-in-gasoline scenario raises serious concern. When diesel fuel contaminates gasoline, it leads to a significant reduction in the octane rating of the gasoline. Octane rating is a critical measurement of a gasoline’s ability to ignite at the right time in the engine’s cycle. With diesel, which has an octane rating between 25-40, even a 2% contamination can lower the overall octane rating of gasoline by 1 point. As the diesel content increases, say to 10%, the octane depression becomes more severe, lowering the rating by up to 5 points, creating problems in most car engines. The heavier diesel can also sink to the bottom of the gas tank, causing issues during injection into the cylinder. This can lead to partially-burned diesel fuel leaving deposits on pistons, valves, and spark plugs, causing the car or truck to run terribly. Continued driving in this state could result in serious damage, including the risk of hydro-lock in the cylinders, potentially leading to a blown head gasket or a cracked cylinder head. Moreover, if unburned diesel fuel enters the exhaust system, it might ignite in the catalytic convertor, destroying it and necessitating an expensive repair job.

The Bottom Line – Don’t Drive It

When it comes to mixing fuels, especially gasoline in a diesel engine or vice versa, the bottom line advice is clear: don’t drive the vehicle. It’s impossible to know the exact amount of the wrong kind of fuel in your tank and fuel system. If you have good reason to believe that the wrong kind of fuel was accidentally added, the safest course of action is to have the vehicle towed to a mechanic’s garage to remedy the problem. Once there, the mechanic will likely remove all the fuel, flush the system, and remove any problem fuel. While you might hear stories from a friend, coworker, or relative about how they drove their car after a fuel mix-up and it was fine, these situations can’t be compared. Human nature tends to minimize the description of potential problems, especially when one is responsible for the mistake. You’ve been warned, and it’s not worth taking the chance. The risks outweigh the convenience, and proactive measures can prevent further damage.

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