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Engine Alert: The Perils of Aged Gasoline!

What happens to fuel when it gets old? Does old fuel damage the engine?

The Deterioration of Gasoline and Its Impact on Engines

From my years of tinkering with engines, I’ve seen firsthand how gasoline, if not stored properly, begins to evaporate. When it’s not sealed in an airtight container, it undergoes a transformation, losing its explosive volatiles. This phenomenon is not just limited to petrol; even the fuel in your lawnmower can suffer the same fate. There comes a stage when the old fuel becomes so degraded that it refuses to start the engine. I remember having to empty my lawnmower and fill it with fresh fuel; only then did it fire up straight away. This is a common issue, as I’ve heard from more than one mechanic.

The process where fuel turns into a gel-like substance or even into a varnish-like coating can be difficult to remove. In such cases, carburetors and fuel pumps in small engines need extensive cleaning or replacing. The fuel system becomes clogged, necessitating taking apart and rebuilding the carbs. I recall a time when old gas in my car’s engine turned into a jelly consistency, making it almost impossible for the engine to start. The carburetor and other parts of the fuel system needed deep cleaning.

Moreover, old gas can burn improperly, potentially triggering your check engine light. This is an indication that the vehicle is malfunctioning in various ways. For instance, it might fail to start, idle differently than usual, or lose power while driving. In my experience, adding a fuel stabilizer can help to some extent, but it’s not a complete solution. The real problem lies in the tank, sending unit, and lines, where the old fuel wreaks havoc, requiring thorough intervention.

If you run a gasoline engine indefinitely with unlimited fuel, what will be the first cause of failure? 

The Inevitable Wear of Continuous Engine Operation

In the world of continuous engine use, particularly in gasoline engines, the first sign of wear often comes from a component we rarely think about: the timing chains. I’ve seen this in various automotive applications, like when a company I knew ran a limousine service between Connecticut and NY airports. They used stretched Chevy Suburbans, powered by 5.7 liter V8 engines. Up until 1990, the most common failure in these robust engines was the timing chains. Remarkably, this only occurred after about 600,000 miles. Later, GM made changes to the design, but then failures began appearing at around 300,000 miles.

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In contrast, when you look at marine applications, the scenario changes. Here, engines, including their larger cousins, are pushed to their limits, often operating at 70–80% of full speed. This is the equivalent of driving a car at 99–100mph for 200,000 miles. Despite this intense use, it’s not unusual to find 50-year-old pleasure boats with their original engines in working order, especially in climates with a short boating season. The useful life of these engines is often capped at around 2000 hours, but it’s not just about the hours clocked; it’s how they’re worked and abused. Older models, particularly those with wood hulls, often died due to other factors before the engine gave out.

Can dirty fuel damage an engine?

The Perils of Contaminated Fuel in Engines

The presence of dirty fuel can wreak havoc on engines, especially in cars and vehicles where precision is key. Fuel filters are designed to catch debris like grains of sand or metal shreds, but sometimes these contaminants still find their way into the combustion chamber, adhering to the walls, pistons, and valves. This buildup, particularly carbon, makes it tougher for the engine to start or idle smoothly. As the cylinders and throttle body become clogged, the engine’s efficiency drops significantly. In severe cases, it even requires taking the head off the engine to clean these components thoroughly. It’s also worth a mention that this clog can extend to the fuel injectors, further complicating the situation and necessitating professional intervention to restore engine performance.

How Old Gasoline is a Threat to Your Car Engine

The Hidden Dangers of Aged Gasoline in Automotive Engines

Gasoline, often lauded for its convenience as a fuel for automobiles, presents a unique problem when it breaks down over time. Unlike electric cars, where charging the battery takes hours, refueling a gasoline-powered car is a matter of minutes. However, when gasoline becomes old, it transforms into a thick varnish. This varnish-like substance can clog the finer components of your engine, leading to a range of issues such as rough idling, a loss of power, and even the inability to start the vehicle. The problems caused by old gasoline are not just inconvenient but can be seriously harmful to your automobile, requiring extensive remedies to rectify.

What Problems Can Old Gas Cause?

The Impact of Aged Gasoline on Vehicle Performance

When gasoline sits in a fuel system for too long, it begins to degrade, turning into a thick varnish that coats and clogs key components. This is especially true for carburetors and fuel injectors, where the small jets become vulnerable to blockage. As a result, the vehicle starts to run poorly. Symptoms include difficulty accelerating, a loss of power, and a refrain from starting. In my experience, clogged components can even cause the engine to miss or cease idling, leading to frustrating moments where you’re left trying to start a stubborn engine.

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Another critical area affected by old gasoline is the fuel pump and sensor. Over time, the aged fuel can diminish the function of these parts, making it difficult to read fuel levels or pump fuel efficiently from the tank to the engine. This often results in a stoppage of fuel flow, affecting the engine’s performance. Moreover, in the cylinders, old gasoline leads to carbon buildup, which sticks to the walls, increasing friction and wear, thus reducing efficiency. This excessive buildup can even trigger the check engine light, signaling increased emissions and further starting difficulties.

What Can You Do About Old Gas?

Effective Strategies for Managing Aged Gasoline in Vehicles

To prevent old gasoline from affecting your automobile, there are several proactive measures you can take. First, using premium or super unleaded gasoline with a higher octane rating can significantly reduce carbon buildup. This type of fuel is less prone to degrading into varnish, which is a common issue with standard gasoline. Additionally, adding a fuel stabilizer to your gasoline can be extremely useful, especially if your vehicle is going to sit for weeks or even years without being driven. However, if you’re already facing a problem where old gasoline has affected your fuel system, mere cleaners might not be enough to fix the issue. In such cases, it’s often necessary to have the components taken apart and cleaned by a qualified mechanic. Some parts might even need to be replaced to restore lost functionality and ensure your car runs smoothly again.

Can old gasoline cause an engine to not start?

The Impact of Aged Gasoline on Engine Ignition

Yes, old gasoline can indeed cause an engine to not start. This issue became apparent to me with my ’89 BMW 325i that sat in my garage. It used to start up monthly, but over 3-4 months, it became progressively harder to ignite. One weekend, it just kept cranking without success. The culprit? The tank was half-filled with gasoline that was 6 months old. In such cases, draining the old fuel and refilling with fresh gasoline often helps. Adding a fuel stabilizer can prolong the lifespan of the gasoline, preventing it from turning stale or varnish-like. If the sparkplugs have become fouled by the old gas, they might need changing. Using products like Techron cleaner or Seafoam can further assist in cleaning the fuel system when you run the car for about 10-30 miles after refueling. While some might blame the age of the fuel, often evidenced in cars that always have old gas sitting in them for extended periods, it’s a definite problem. Siphoning out the old gas and using a starting fluid can sometimes get the engine running again, proving that deteriorated fuel was the issue.


Don’t try to start a long-dormant engine without checking the gas tank for goo

The Risk of Ignoring Aged Gasoline in Long-Standing Vehicles

One critical piece of advice for anyone resurrecting long-dead cars: never start an engine that’s been sitting for years without first checking the gas tank. I learned this the hard way with a BMW 2002tii tribute car I received. It had a transplanted fuel-injected motor and a braking system, but was largely a rust-covered parts car. Despite my initial desire to disassemble it, I eventually decided to sell the car whole. However, before making it available to a potential buyer, I knew I had to assess the condition of the fuel system.

The Process of Evaluating and Cleaning Old Fuel Systems

My first step was a simple but telling gross assessment: unscrewing the filler cap and taking a whiff. The overwhelming stench of varnish was a clear sign that the tank needed to be drained and cleaned. Upon removing the fuel level sensor and inspecting the tank with a flashlight, I discovered a sticky mess of rust, sediment, and gooey deposits. This situation was akin to entering a furniture refinishing workshop due to the pungent smell.

Dislodging Sediment and Cleaning the Fuel Tank

Next, I pulled the tank from the car, threw an old chain inside, and shook it to dislodge sediment and rusty scale. After rinsing it out and letting it dry overnight, I found large patches of goo, reminiscent of Silly Putty, stuck to the bottom. It took meticulous scraping and rinsing to clear the crater-like recess where the pick-up tube sits. This hands-on approach, though challenging, was a more practical and budget-friendly alternative to getting the tank professionally boiled out at a radiator shop.

The Hidden Dangers in Fuel Pumps and Injectors

It’s a fantasy land to think that the fuel pump and injectors wouldn’t be affected by this sludgy mess. The car’s fuel pump, a horizontally-mounted canister-like electric pump, was seized due to the solidified old gas. After powering it with a battery, I had to take it apart to examine and clean the damage. The brown goo inside was a molasses-like substance, far from the clean state a functional fuel pump should be in.

Cautionary Measures Before Starting the Engine

Finally, before even thinking of turning the key and cranking the engine of a long-dormant car, it’s crucial to replace the old gas with fresh fuel and install a new filter. The risk of fresh gas softening and dislodging the varnish, potentially causing it to lodge in the carburetor jets or fuel injectors, is too high. In short, the start-up of a vehicle that’s been inactive for extended periods is a meticulous process that demands thorough cleaning and preparation to avoid damaging the injection system.

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