Understanding the issues surrounding unused fuel in vehicles left in storage


Fuel Types [3] [7] [8] [9] [10]

The most common automobile fuels are now designated with an E moniker. The designation is indicative of ethanol content in fuel. It is a ‘by volume’ measurement. Most common automobile fuels (over 90% of the US market) now contain ethanol.

E10: up to 10% ethanol in fuel. All cars can use this fuel type and it is the most common gasoline blend sold today.

E15: up to 15% ethanol in fuel. Only vehicles made after 2001 can use this type but in reality many engine manufacturers do not support a warranty claim if gas with ethanol levels greater than 15% is used.

E85: 85% ethanol fuel, used by Flex-Fuel vehicles only.

E0: no ethanol content, also known as pure (‘neat’) petroleum fuel (but now can be difficult to source).

Besides the E designation, an automobile fuel is classified according to octane level. Simply put this is a measure of the ability for a fuel to withstand pre-ignition (also known as pinging – more below). The higher the number the better the engine performance and better the engine life, all things held equal. Today’s fuels use ethanol as an octane booster. Pure ethanol has an octane rating of 113 – 114.

What Happens to Fuel When it is Stored? [5][6][12]

Phase Separation

The single most important issue for stored gasoline is phase separation. The alcohol (as ethanol) absorbs water rather easily (alcohol being a hydrophilic substance). Free water is available through direct air contact (humidity), storage tank leakage or through temperature change and condensation of absorbed water in a fuel mixture. At a critical point (Saturation point) the alcohol and water will settle to the bottom of any tank (large or small) due to density difference. The gasoline left above (in the tank) will have a lower octane rating. The bottom material will not ignite in a modern combustion engine. Some refer to this deposit as “gum”.


Varnish is the residue of old fuel left on engine surfaces. Hot engine shutdowns can lead to ‘heat soak’ whereby rapid fuel evaporation on the tips of the injectors leaves a residual varnish that can cause future engine system clogging.

Lowered Octane Level

The gasoline blends of today are given an octane boost through the added ethanol (previously performed by a chemical additive called MTBE). As a consequence of water-induced phase separation, fuel blends can end up with lower octane than specification and become unusable (and the fuel may have to be disposed of with clear cost consequences).

How long does it take for Phase Separation to occur? [5] [6]

Phase separation of a water-ethanol mixture from gasoline will occur for a variety of factors and at differing rates. The critical measure is the saturation point (0.05% H2O at 60 oF) as it is this concentration whereby the water-ethanol mixture separates from the gasoline and settles to its respective container bottom.

Clearly any direct contact with water will accelerate the rate at which phase separation will occur. Tank condensation, contaminated fuel containers, vent seal leaks and container cracking are all direct means of moisture addition.

Temperature greatly affects the phase separation point. For example, a drop in ambient temperature from 60 oF to 28 oF will reduce the water carrying ability of an E10 fuel mixture by approximately 33%.

Most common gasoline-ethanol blends will start to breakdown after 30 days. Fuel does go stale just like milk and bread. The oxidation ability of ethanol in the fuel accelerates the ‘going stale’ process. In addition, over time, as a gasoline source is subjected to multi transfers and ‘re-fills’, moisture will inevitably enter the mixture (mostly through air contact). Operators and vehicle owners need to be aware of this fact and react accordingly.

What Damage can be caused by Expired and Old Fuel? [5][13]

  • Corrosion
    Fuel that has phase separated is corrosive, namely the high ethanol concentrate at the bottom of an affected storage vessel. This can cause damage to non-metallic and rubber components (gaskets, hoses, O-rings, etc.) in storage tanks, ancillary dispensing equipment and ultimately the automobile fuel system. It is important to understand when phase separation has occurred to prevent this material from contacting areas sensitive to corrosion.
  • Pinging
    Pinging in an engine (that knocking sound heard when a vehicle accelerates) is a result of poor combustion within the engine chamber and can be caused by a variety of factors. Aged fuel that has a low octane content can cause pinging as early combustion occurs. The fuel mixture ignites prior to spark plug firing leasing to dual flame front collisions (to be technical).
  • Clogged fuel system components
    The gum of partial to full phase separated fuel can clog fuel lines and injectors, coat engine components such as valves and carburetors, lead to sensor issues and plugged catalytic converters.

Any varnish particulate deposits can lead to plugged injectors, fuel spray delivery problems and engine issues ranging from delayed acceleration and stalling to poor fuel economy. In extreme cases valve stems can stick from varnish deposits causing extensive engine damage.

How to Prepare Fuel for Storage? [1][8]

  • Fuel tank
    The ideal fuel preparation for storage of a vehicle is to empty the fuel tank. This may be a challenge for some operators (on a few levels) and could lead to future varnishing issues (and condensation) if not done correctly. As a minimum it would be best to fill a tank (to 95% level) to prevent any condensation potential. It is important to remember that once a fuel becomes stale and phase separation occurs, no amount of re-mixing will restore the fuel.
  • Ideal environment for fuel storage
    Temperature has a significant impact of fuel stability. High temperature (along with high humidity) is the main situation to avoid. Storing fuel (and the vehicles in which it rests) in a cool, dry environment is preferred. A stable temperature below 80 oF is a good guideline to follow.
  • Best fuels to use for vehicle storage
    The use of conventional E0 gasoline is the best fuel to use when storing a vehicle (with residual fuel). While not readily available, it can still be purchased in some states and locales. Use online forums such as GasBuddy.com and REALGAS.com to locate but there is no guarantee that it is available in all areas. The ethanol content is not controlled at the refinery but at the distributor level.
  • Fuel treatment
    One means to keep the residual fuel from breaking down is to add a commercially available fuel (ethanol) stabilizer to the fuel tank before putting the vehicle into storage. The product is best added to a full fresh tank and it is recommended to run the respective engine for 5 minutes to ensure proper mixing.

1. Gold Eagle Co. http://www.goldeagle.com/engine_care/411onethanol.aspx

2. Gold Eagle Co. Changes in Gasoline IV  http://www.goldeagle.com/UserFiles/file/Ethanol%20411/Changes_in_Gasoline_Manual_IV_Updated_Logo.pdf

3. U.S. Energy Administration http://www.eia.gov/tools/faqs/faq.cfm?id=27&t=10

4. U.S. Department of Energy http://www.fueleconomy.gov/feg/ethanol.shtm

5. National Petroleum Equipment CO. http://nationalpetroleum.net/Ethanol-Water-Phase-Separation-facts.pdf

6. Popular Mechanics http://www.popularmechanics.com/cars/alternative-fuel/biofuels/e15-gasoline-damage-engine

7. Fuel-Testers http://www.fuel-testers.com/gasoline_octane_and_ethanol_E10.html

8. Fuel-Testers, Ethanol Laws State by State Guide http://www.fuel-testers.com/state_guide_ethanol_laws.html

9. Fuel-testers, Precautions/Tips for Use of E10 Gas http://www.fuel-testers.com/ethanol_engine_precautions.html

10. Pure-gas.org http://pure-gas.org/

11. Union of Concerned Scientists http://www.ucsusa.org/clean_vehicles/smart-transportation-solutions/cleaner_fuels/ethanol-and-other-biofuels/the-truth-about-ethanol.html

12. Varnishing http://saturdaymechanic.com/ethanol-issues-varnish-vs-gum-and-using-the-right-additive/

13. Pinging http://repairpal.com/what-is-engine-pinging

14. General comments on Ethanol in Fuel http://www.williammaloney.com/Misc/EthanolProsConsDrawbacks.htm


Preserved 1971 Buick GS 455 Stage 1 – Stored from March 2004 – September 2013

This 1971 Buick GS Stage 1 455 is a prime example of the benefits of storing a classic car.  The vehicle was purchased in 2001 from the original owner. With original paint, 54,000 miles, factory chrome and interior, this car is what many would have considered a true “survivor”.  Although this vehicle remained remarkable condition for over 30 years, several years after it was acquired by its second owner, the car underwent a complete restoration to return it back to the condition it was in when it was purchased new in 1971.

1971 Buick GS

circa 2004 – 2 days out of the paint booth

If your familiar with car restorations then you know that this can be an off and on process that extends over many years.  This particular restoration took place over 9 years and was carried out in a section of the same building where Seekonk Car Storage is currently located.  Over the course of this 9 year restoration the vehicle was stored in the premium car storage section of Seekonk Car Storage when the car was not being worked on.

circa 2013

circa 2013

The restoration recently came to end in August of 2013 and even though 9 years has gone by since the restoration process began the car appears as though it was restored yesterday.  The flawless glass finish paint job, detailed chassis, engine compartment, un-restored chrome bumpers and replacement pearl white interior show no signs of deterioration typically found on vehicles stored for long periods of time.

Below are photos of the car taken in August 2013.

driver rear quarterDSC_2543

DSC_2548 - CopyDSC_2547 - Copy





1969 Camaro – Keeping Top Down During Storage

Over the weekend I decided take our 1969 Camaro RS SS out of storage.  But unfortunately it’s not 100% ready to go.  There’s still a bunch of little things that need to be done to get the car back on the road for the summer.  Having more than one classic car is great, however the downside is making the time to maintain each car.  This one in particular never really got finished from the restoration work we did on it about 5 years ago.  Still on the “to do list” is the installation of a new passenger side mirror, gauges under the dash to monitor the temp and oil pressure, new top and vacuum lines for the vacuum operated hideaway headlights.

1969 Camaro SS 350

Latching a Top that Was Left Down During Storage

This particular car is a convertible, and since the top is not in very good condition we leave it down all the time, even during storage.  I do not recommend that anyone does this by the way.  It is very difficult to get the top back up if it is left down for a long period of time.  If you do leave the top down, when you try to put the top up and latch it to the header bar, the top will seem like it’s too small for the car.  Sometimes what I do in this situation is back off the top hooks to extend them out closer to the header bar.  By doing this you should be able to grab the header bar with the hooks and get the top latched again.  After you get the top latched, take one side off at a time and turn the hook in a few turns and re-latch it again.  Keep doing this until the top fits the way it did before you left it down.

1969 Carmaro top down