Premium gasoline, also known as high-octane gas, is a higher grade of fuel compared to regular unleaded gasoline. It has a higher octane rating, generally 91 or above, meaning it can withstand compression better before igniting. This allows it to be used in high-performance engines so they can operate at higher compression ratios without knocking or pinging. But how long can you store premium gas in your car’s tank before it goes bad?
Why Use Premium Gas?
There are a few key reasons why certain vehicles require or recommend premium gasoline:
- High compression engines – Higher compression ratios improve power and efficiency but require higher octane to prevent knocking.
- Turbocharged/Supercharged engines – These force more air into the engine, raising cylinder pressures and temperatures, necessitating higher octane.
- Sports cars and luxury vehicles – Often have large, powerful engines needing premium fuel.
- Tow/haul usage – The extra load requires higher octane to prevent engine knock.
- Manufacturer recommendation – Some manuals specify premium gas for optimal engine performance.
So for these types of vehicles, it’s important to use the recommended high-octane gasoline to get the advertised performance while avoiding engine damage from knocks or pings.
How Long Does Gasoline Last in a Car?
In general, gas has a shelf life of 3-6 months when properly stored in an airtight container. However, gas begins to degrade as soon as it’s pumped into your car’s gas tank due to exposure to oxygen and temperature fluctuations.
Here are some estimates for how long gasoline lasts in a car:
- 1-3 months – Gas can start deteriorating in as little as a month. After 3 months it can begin causing issues.
- 6 months – Most gas today contains stabilizing additives to last 3-6 months in a car’s tank.
- 1 year – Gas can still be used for up to a year, but may cause clogged injectors and deposits.
Problems from old gas usually occur when a car sits unused for an extended time. The gas oxidizes and varnishes form, clogging fuel injectors and reducing combustion. Moisture buildup can also happen over time leading to corrosion.
Does Premium Gas Last Longer?
There is no evidence that premium gasoline inherently lasts longer than regular in storage. It has a higher octane rating thanks to more octane-boosting additives, but does not contain more preservatives or stabilizers to extend its shelf life.
Many major gasoline brands supplement both regular and premium gas with the same stabilizing additives to maintain quality for around 3-6 months in a car’s tank. So from a chemical standpoint, premium fuel does not last noticeably longer than regular before going stale.
However, premium’s higher octane rating does give it a slight advantage in retaining its optimal quality and performance characteristics as it ages. The octane acts as a buffer against the small drops in octane that can occur as gasoline oxidizes and degrades over time.
Advantage of Higher Octane
As premium gasoline sits in a car’s tank, a few things happen:
- Octane rating decreases slowly from oxidation.
- Heavier, less volatile compounds accumulate from evaporation.
- Gum, varnish and moisture build up.
This makes the gasoline less ideal for high-compression engines. But premium’s extra octane provides room for these small losses over time before falling below an engine’s requirement and causing knocking or performance issues.
An engine tuned for 91+ octane premium gas can potentially experience fewer odd combustion events from minor octane losses than if it was running on 87 octane regular that dropped to 84-85. So the higher octane rating of premium does give it a bit more durability.
Caveats
However, there are some caveats:
- Higher octane alone does not clean fuel injectors or prevent moisture buildup.
- Prolonged storage will still cause issues as additive packages deplete.
- Always follow manufacturer recommendations for required fuel grade.
So while premium may retain peak engine performance a bit longer into storage, extended sit times will still necessitate periodically running the engine and adding fuel stabilizer to combat long-term fuel degradation.
Tips for Storing Premium Gas in a Car
To maximize how long premium gas lasts in your car, here are some helpful tips:
Use Fuel Stabilizer
Add fuel stabilizer to completely filled tanks. Stabilizers contain antioxidants and corrosion inhibitors to preserve fuel quality during storage. Follow manufacturer recommended dosage rates.
Fill Tank Completely
Minimize air space at the top of the tank to limit oxidation. Opening the gas cap also allows moisture in.
Store in Cool, Dry Place
Store vehicles away from direct sunlight and extreme temps. Fuel stability decreases with higher ambient temps.
Drive Regularly
Regular use ensures fresh gas cycles into the tank. At minimum, drive every 1-2 months to combat deterioration.
Check Owner’s Manual
Follow any additional gas storage guidance provided in your vehicle owner’s manual.
Signs of Bad Gasoline in Your Car
Here are some common indicators that the gasoline in your car has gone bad:
- Hard starting or stalling after starting
- Rough idle and misfiring
- “Knocking” or “pinging” sounds from the engine
- Power loss and reduced acceleration
- Increased exhaust emissions
- Fuel filter clogging prematurely
- Gum or varnish buildup in fuel system
These issues typically occur after gas has been sitting in a tank for longer than 3-6 months. Bad gas can damage injectors, cylinder walls, catalytic converters and oxygen sensors if not addressed promptly.
What to Do With Old Premium Gas
If your high-octane gasoline has expired from sitting too long, here are some options:
Add New Gas
Fill the tank most of the way with fresh fuel. The new gas will mix with the old and help resolve issues.
Use Fuel System Cleaner
A gasoline or fuel injector cleaner containing PEA can help clean deposits from stale fuel.
Drain Tank & Change Filter
Siphon or drain the old gas if it’s severely degraded, and replace the fuel filter.
Consult a Mechanic
If you have engine problems or don’t feel comfortable doing the work, have a mechanic inspect and address any issues.
Discard Safely
Properly dispose of severely degraded gas. Don’t dump it — check local oil recycling centers to safely dispose of it.
Conclusion
Premium gasoline can generally last 1-6 months in a car’s gas tank before beginning to deteriorate. While it does not inherently last longer than regular unleaded when stored, its extra octane provides some buffer against performance-impacting drops in octane as gas ages. Using fuel stabilizers, keeping tanks full, and regular driving can extend premium gas life. Watch for signs of bad gasoline like knocking or hard starting, and be prepared to drain tanks and clean fuel systems if gas is stored too long.