Fuel Preservative

[martrirl]

I have been told that if I do not use at least a full tank of gas a month in the off season I should add fuel stabilizer to my tank.  Depending on how much snow we get, I might not be driving that much.  Should I add stabilizer to my fuel?

[Wellardmac]

Okay, longer answer now that I have time.

Here's a quote directly from a ChevronTexaco website. This is typical of all gasoline:

"22. How long can I store gasoline without it going bad?
Gasoline stored in a tightly closed container in a cool place will stay good for at least one year. It is better if the container or fuel tank is almost (95 percent) full. If the container or fuel tank will be in the direct sun or will be heated above 30°C (80°F) much of the time, add an aftermarket fuel stabilizer to the gasoline when you first buy it. Gasoline-oil blends for two-stroke cycle engines stored under the proper conditions will keep as well as gasoline itself."

The key is the full tank. Gum formation happens through an oxidative process, if the tank is full, there is no oxygen to get into the fuel - assuming that the tank is well sealed. Gasoline doesn't readily absorb oxygen, although, high ethanol content gasolines will absorb more O2. If you are on the east coast during the winter, the temperatures are well below 30C and the oxidation process is even slower, so you have no fear at all of degradation of the fuel.

Not only does a full tank of gas help keep your fuel stable, but it also is safer. A full tank prevents a head-space of flammable gasoline vapor and will prevent ignition. As an aside, you can stick a match into fuel and it will not burn, only the fuel vapor is flammable.

If you're in California or Florida during the Summer, then the story is different, but we're talking about Winter storage here. If you have your car sitting with a full tank of gas over the Winter you will see no issues.

Hopefully this will help you feel a little more comfortable.

[Phil G.]

There are a number of excellent posts on winter storage on the Rennlist site. I'm planning on using Stabil with a full tank of fuel for the winter months. It's available at Autozone, Walmart, etc.

[Wellardmac]

Help me understand why you would add something that clearly doesn't need to be added.

[Phil G.]

It's my understanding that gasoline is less stable than in the past with the additives that are input at the refinery (no I don't have proof for that claim). For those of us who do plan to store our cars over the winter months, I personally feel more secure adding a reputable fuel stabilizer to a full tank of gas prior to storage. I'm not alone in this view. You are certainly free to do what you wish. Others claim that an oil additive is needed as well, as both gas and oil tend to absorb ambient moisture - even with a 'closed' system.

Phil

 

[Wellardmac]

Phil,
Absolutely, do whatever you're comfortable doing. But, the assertion that gasoline is unstable without stabilizers is totally without merit.

As you know, my background is in the chemical industry - I know the components that go into gasoline and I know that there's no chemical basis that requires the addition of stabilizers to gasoline.

The fuel has adequate stabilizers and a full tank will be perfectly fine over the winter. The tank will not be in a position thermodynamically, or kinetically for degradation.

That being said, even though there is no chemical basis for adding stabilizers to the fuel and it adds no real functionality to the fuel (that it does not already have), I know that some are happy spending money for piece of mind.

The real key to this is having a full tank of fuel. A sealed system will not accumulate water or degrade over the winter - I know that for a fact and it is well tested and documented in the scientific literature.

[Phil G.]

Thanks for the advice - it's actually reassuring that failing to add a stabilizer won't harm the system. I'm assuming that doing so won't either. Completely agree the key is having a full tank when the car's stored.

Phil

 

[Wellardmac]

Bingo!

Remember to refill your tank if you take it out over the winter.

A tank that is less than 95% full has more oxygen in it and has the possibility of degradation of the additives (it's actually the additives that degrade in the fuel, not the fuel itself) - that degradation is what provides the possibility of gum formation in your fuel and leaving deposits on your injectors.

In terms of water adsorption, the head spaace in your tank also plays a role. Fuel itself does not absorb water (too hydrophobic - water hating). Unfortunately, the ethanol that is now added to fuel can absorb water. Thankfully it's only present in a few percent of the fuel. You have to ask where the potential for water exists... air fuel contact, or an open system. A sealed tank is not open and thankfully, Winter air is very dry, so the chances of water problems with fuel are minimal.

Now, all that being said, it's a totally different question for non-winter storage and that would be a very different discussion.

[martrirl]

Thanks for all the great information.  I will keep my tank topped up for the winter.

[Wellardmac]

You're welcome! Glad to be of help.