Winter Storage with Full Tank Of Gas or Not?

Given the debate over the benefits of storing your rig with a full fuel tank of gas or one nearly empty, I should mention that it is "NOT" a good idea for most vehicles these days to run your fuel tank below 1/4 full. The reason is that the electric fuel pump is located inside the fuel tank standing upright in most cases, attached to the fuel gauge sending unit. 1/4 full keeps the fuel pump at least partially submerged in fuel which keeps it running cooler. The life of your fuel pump will greatly extend if always running cooler. Fuel pumps are expensive to replace. Never let your fuel go below 1/4 full and your fuel pump may never let you down.

That was a tip given to me from a very good auto mechanic.

A quick search on fuel pumps and I found this motor home applicable example, shown with accommodations for a generator fuel-tap. The fuel pump is the silver cylinder at the bottom.

Diesel is a pretty good solvent too, you’re saying it’s not an oil?

As I stated previously, read the MSDS of both products, you’ll find they’re remarkably similar.

JaxDad wrote:
According to the MSDS GM Top Engine Cleaner is (they keep the exact formula secret) 75% or more petroleum distillates, I.E. oil.

GM Top Engine Cleaner MSDS

Did you actually read this? BTW, most petroleum distillates in this end up being solvents.

I would use this WAY before I poured SeaFoam in which is close to 50% oil.

Your tank does of course vent in but it's not breathing in and out like you claim it is. Even if it did, it would not make a difference. Marine tanks are totally vented and there is ZERO condensation issues.

Did you even read this link:
Fuel Tank Condensation Myth


For every 27°F increase in temperature, liquid gasoline expands 1%.

babock wrote:

JaxDad wrote:

Fuel tanks breathe, as the liquid and air warm up they expand and push out air, that evening they cool and condense pulling in replacement air which is generally very moist and the cycle starts all over again. This happens all year long, anytime it’s warmer during the day than it is at night.

Fuel tanks do not "breathe".

So when I fill my coach, 75 gallons, and then drive 600 miles you’re saying my empty tank is then a crumpled up ball of tin because it collapsed from not being vented?

Or that when I fill my 75 gallon tank with fuel coming out of a buried tank full of gasoline that’s about 50 deg F. and then park it in 90 deg. F. heat the tank somehow expands to absorb the increased volume?


According to the MSDS GM Top Engine Cleaner is (they keep the exact formula secret) 75% or more petroleum distillates, I.E. oil.

GM Top Engine Cleaner MSDS

ron.dittmer wrote:
They "DO" breathe. They exhale through a charcoal canister for the purpose of emissions.

The charcoal canister captures the fumes and returns the raw fuel collected to be burnt. No fuel vapor is EVER released anymore.

Even with boat fuel tanks this isn't an issue and they are vented. In fact Mercruiser states in their owner's manuals to leave the tank as empty as possible. They used to say full but have changed their recommendation.

If there really was a problem with water condensing inside a fuel tank, you would see sweat forming on the outside of a fuel tank as well. When was the last time you saw a fuel tank sweating? Right...never!

babock wrote:

JaxDad wrote:

Fuel tanks breathe, as the liquid and air warm up they expand and push out air, that evening they cool and condense pulling in replacement air which is generally very moist and the cycle starts all over again. This happens all year long, anytime it’s warmer during the day than it is at night.

Fuel tanks do not "breathe". Even if they did "Breathe", the amount of air being pushed in and out is tiny. Any vehicle built in the last 25 years, including RV's has a fuel system that is sealed to the air for emissions reasons.

They "DO" breathe. They exhale through a charcoal canister for the purpose of emissions. If they didn't breathe, the engine would die from the starvation of fuel somewhere between a full tank and an empty tank of gas, via a created vacuum.

You would be surprised how much air is drawn daily and and exhaled through the charcoal canister. As JaxDad stated, it is a daily process. Temps outside often swing 30 to 40 degrees between the heat of the day and the low during the night which causes the breathing action. That action is minimized with a full tank of gas. Less air in the tank means less air to breathe. With a full tank of gas, there might be so little air that the system isn't breathing at all.

JaxDad wrote:

Fuel tanks breathe, as the liquid and air warm up they expand and push out air, that evening they cool and condense pulling in replacement air which is generally very moist and the cycle starts all over again. This happens all year long, anytime it’s warmer during the day than it is at night.

Fuel tanks do not "breathe". Even if they did "Breathe", the amount of air being pushed in and out is tiny. Any vehicle built in the last 25 years, including RV's has a fuel system that is sealed to the air for emissions reasons.

Sorry, you do not put anything in your fuel tank that has oil in it. If your going to use something, use something with PEA(Poly Ether Amine) that will actually do something good. The GM top engine cleaner does not have oil in it.

JaxDad wrote:

babock wrote:
Leave the tank without filling and just fill up in the spring.

Condensation in fuel tanks is a myth. If you had a 100 gallon fuel tank and it was completely empty except for 100% humidity air @ 70° and it all condensed you would get a grand total of 0.22 ounces of water.

The math is correct, the logic is deeply flawed, and since the OP is in Minnesota not California he probably has a valid concern.

The calculation of water content is for a SINGLE tank full of moist air.

Fuel tanks breathe, as the liquid and air warm up they expand and push out air, that evening they cool and condense pulling in replacement air which is generally very moist and the cycle starts all over again. This happens all year long, anytime it’s warmer during the day than it is at night.

JaxDad has it 100% correct.

Yet there is a ray of hope for those who don't fill up their fuel tank for long-term storage. Fuel today contains 10% ethanol which is alcohol which is gas line antifreeze, which is a water displacement. So if you have 10 gallons of fuel in your 55 gallon fuel tank, you have 1 gallon of gas line antifreeze. But still, you don't want to introduce water in your fuel system even though it is addressed via ethanol for the water rusts the bottom of the fuel tank, and rust particles in the fuel system.

babock wrote:
Leave the tank without filling and just fill up in the spring.

Condensation in fuel tanks is a myth. If you had a 100 gallon fuel tank and it was completely empty except for 100% humidity air @ 70° and it all condensed you would get a grand total of 0.22 ounces of water.

The math is correct, the logic is deeply flawed, and since the OP is in Minnesota not California he probably has a valid concern.

The calculation of water content is for a SINGLE tank full of moist air.

Fuel tanks breathe, as the liquid and air warm up they expand and push out air, that evening they cool and condense pulling in replacement air which is generally very moist and the cycle starts all over again. This happens all year long, anytime it’s warmer during the day than it is at night.

babock wrote:
SeaFoam is snake oil. It contains oil,naptha and isopropyl alcohol...that's it folks! And you don't want to run it on engines with O2 sensors..it degrades them because of the oil content.

Call it anything you like but it works, and it works well. It does NOT harm the O2 sensors, in fact it cleans them.

GM sells, or at least did the last time I checked, a ‘top engine cleaner’ which according to the SDS is almost exactly the same formula as SeaFoam is. I doubt they’d tout something as being good for your engine if it would cause damage?

The ‘oil’ is lighter than kerosene and when diluted to the extent it is in a fuel tank is a very tiny percentage of what goes through the engine.

Leave the tank without filling and just fill up in the spring.

Condensation in fuel tanks is a myth. If you had a 100 gallon fuel tank and it was completely empty except for 100% humidity air @ 70° and it all condensed you would get a grand total of 0.22 ounces of water.

If you don't believe my math, read this article:
http://www.yachtsurvey.com/myth_of_condensation_in_fuel_tanks.htm
It's discussing boat tanks which is even more worst case than RV fuel tanks.

SeaFoam is snake oil. It contains oil,naptha and isopropyl alcohol...that's it folks! And you don't want to run it on engines with O2 sensors..it degrades them because of the oil content.