Generator won't start after sitting for a while? Old gas often clogs vital parts, leading to real frustration. The good news is, fixing it is usually simpler than you might think.
To fix a generator with old gas, you generally need to drain all the old fuel from the tank and carburetor1, clean the carburetor components, replace the fuel filter if it has one, and then refill with fresh, stabilized gasoline.
Old gasoline is one of the most common reasons I see generators fail to start, especially after they've been stored. Over my years helping clients with their generator businesses, this issue pops up again and again. It's a preventable problem, and addressing it correctly can save you a lot of headaches and money. Let's walk through how to sort this out and get your generator ready for action.
How to treat old gas in generator?
Is old gas sitting in your generator's tank? This can stop it from starting right when you need it. Let's look at how to handle stale fuel effectively.
You can treat slightly old gas (a few months) by adding a quality fuel stabilizer. However, if the gas is very old or already causing problems, treatment won't reverse the degradation; removal and cleaning are better.
When I talk to my clients about long-term storage of generator stock, fuel preservation is a key topic. The big question is always whether to treat or replace.
Gasoline begins to degrade surprisingly quickly. After about 30 days, it can start to lose its combustibility and form gums and varnish.
When is Fuel Stabilizer an Option?
A fuel stabilizer2 is a preventative measure. If you know your generator might sit for more than a month, adding stabilizer to fresh gas can extend its life significantly, often up to 12-24 months, depending on the product. It works by slowing down oxidation and preventing the fuel molecules from breaking down and forming deposits. I've found that for clients who manage fleets of generators, using stabilizer routinely saves them a lot in maintenance.
Limitations of Fuel Treatment
Here's the crucial part: stabilizer cannot rejuvenate gas that has already gone bad. If the gas has turned dark, smells sour or varnish-like, or you can see sediment, it's too late for stabilizer to fix it. Adding stabilizer to bad gas is like putting a bandage on a wound that needs stitches – it won’t solve the underlying problem. The fuel has already separated or formed those "viscous residue deposits" I mentioned, which will still clog things up.
Identifying Irreversibly Bad Gas
You can often tell by:
- Smell: Good gasoline has a distinct, sharp odor. Bad gas often smells sour, stale, or like varnish.
- Appearance: Fresh gasoline is usually clear or lightly colored (depending on additives). Old gas can look darker, cloudy, or have visible sediment or separation.
If you suspect the gas is more than 6 months old and wasn't treated, it's usually best to assume it needs replacing, not treating.
How to get old gas out of a generator?
Stuck with a tank full of old, bad gas in your generator? This is a common reason for no-starts. Getting it out safely is your first important step to recovery.
Safely remove old gas by siphoning it from the tank into an approved fuel container. After that, ensure you drain the carburetor bowl and any fuel lines to remove all traces of the old fuel.
I've guided many clients through this process, and safety is always my number one priority. Gasoline is highly flammable, so take precautions.
Safely Siphoning the Fuel Tank
First, move the generator to a well-ventilated area, preferably outdoors, away from any ignition sources like pilot lights or open flames.
- Get an approved container: Use a container specifically designed for gasoline. Don't use milk jugs or random plastic containers.
- Use a siphon pump: A manual siphon pump is the safest way. Avoid siphoning by mouth – it's dangerous and you could swallow gasoline. Insert the siphon hose into the generator tank, ensuring the end is submerged in fuel. Place the collection container lower than the generator tank. Pump the siphon to start the flow.
- Remove as much as possible: Try to get all the fuel out. You might need to tilt the generator slightly (if safe to do so) to get the last bits.
Draining the Carburetor and Fuel Lines
Once the tank is empty, the old gas in the carburetor and fuel lines still needs to go. This is where the real problems usually hide.
- Locate the carburetor drain screw: Most carburetors have a small screw or bolt at the bottom of the float bowl. Place your approved container underneath.
- Open the drain: Loosen the screw, and fuel will drain out. Let it drain completely.
- Flush (My Preferred Method): As per my insights, this is where a good flush can help. With the drain screw still open (or removed), pour a small amount of fresh gasoline into the fuel tank. Let it flow through the fuel line and out the carburetor drain. This helps push out any remaining old fuel and some loose sediment. I often tell people to do this a few times with small amounts of fresh gas. Some residue might even come out.
- Fuel Filter: If your generator has an inline fuel filter, it's wise to replace it now, as it can also trap gunk from old gas.
Tighten the carburetor drain screw once done.
Proper Disposal of Old Gasoline
Don't just pour old gasoline down the drain or on the ground! It's hazardous waste. Check with your local waste management facility, auto parts store, or fire department. They often have designated collection days or sites for old fuel.
Can you start a generator with old gas in it?
Tempted to just try and start your generator with that old gas still in the tank? This can lead to poor performance or even damage. It's important to understand the risks involved.
Starting a generator with old gas is generally not recommended. It may fail to start, run very poorly, or cause gummy deposits to further clog the carburetor and fuel system, making future repairs more difficult.
I've had many customers ask me this, hoping for a quick fix. From my experience in the generator industry, trying to power through with bad fuel usually creates more problems than it solves.
Why Old Gas Prevents Starting
Old gasoline loses its volatility over time. This means it doesn't vaporize as easily. For an engine to start and run, fuel needs to mix with air in a fine mist – a process called atomization, which happens in the carburetor.
- Reduced Volatility: Old, less volatile gas doesn't atomize well. This makes it hard for the spark plug to ignite the fuel-air mixture.
- Gum Deposits: As I mentioned in my insights, "gasoline gradually volatilizes over time, leaving viscous residue deposits that obstruct the precisely calibrated components within the carburetor." These sticky substances can clog the tiny passages (jets) and interfere with moving parts like the float needle in the carburetor. If these are blocked, fuel can't flow correctly, or at all.
Potential Damage from Using Old Fuel
Even if you get the generator to sputter to life with old gas, it's likely to run erratically:
- Rough Running & Stalling: Inconsistent fuel flow leads to uneven engine speed, sputtering, and frequent stalling.
- Increased Deposits: Running old gas can draw more of those gummy residues deeper into the engine's fuel system. This can turn a simple fuel drain job into a full carburetor rebuild.
I remember a client who insisted on trying to run his generator on year-old fuel. It started, ran terribly for ten minutes, then died. The carburetor was so gummed up we had to replace it entirely, a much costlier fix than just draining the old fuel initially.
Short-Term vs. Long-Term Problems
While you might get lucky if the gas is only marginally old (say, a couple of months without stabilizer), you're still running a risk. The short-term frustration of a no-start or poor performance can quickly become a long-term headache of clogged fuel lines, a gummed-up carburetor, and even fouled spark plugs. It's almost always better to take the time to ensure you have fresh fuel.
Conclusion
Fixing old gas issues usually means draining the bad fuel, cleaning the carburetor, and refilling with fresh gasoline. This straightforward maintenance ensures your generator starts reliably and performs well when you count on it.
