Stale gas

Up here we can get ethanol free from some stations, but only in the highest octane, which is much higher priced and unnecessarily high octane for our engine.

 

Here goes another "stale gas" thread. Haven't we discussed these issues enough already? LOL

 

I don’t think so. Main diff’s: maybe about 30% more price, and higher octane, being more difficult to ignite (that’s it’s prime purpose), might drop mpg slightly. On the flip side the lack of ethanol improves mpg.

 

Gas goes stale without ethanol. The alcohol could speed the process up by drawing in more water, but water can protect aluminum parts from ethanol corrosion.

Not bad at all, just paying more for something not needed.

It ignites just fine from the spark. Octane is a measure of how difficult the gas is to ignite by compression. Which is bad in that it leads to the gas igniting when not wanted.

High octane gas might have lower energy content, but it may not. It comes down the exact blend.

Fuel stabilizers use an ounce for every gallon to five gallons, so very likely it's cheaper.

 

My latest bottle of Sta-bil states 1 oz treats up to 2 1/2 gallons, cheaper yet.

 

i just follow toyota recs, no issues in 9 years

 

I see people saying that everything's OK because it's in a sealed tank. What exactly does this mean? I thought gas tanks were vented? That means as the fuel level drops, air comes in and there's air in the headspace above the gasoline.

The car isn't a BEV. Just drive the car and stop the obsessive behavior trying to treat it as such.

 

That's exactly what popped into my head when I saw the title.

No, the Prime's tank is not vented like in a regular gasser. If you want proof, try putting the gas pump nozzle into the filling port on your car. Then, while squeezing the pump handle, push that button by the fill port that tells the car you have closed the fuel door. Get ready to get gas all over yourself.

I run the cheapo E85 (oops. meant to say E10) gas with an occasional tank of top tier. I bought gas twice last year. Once in March and once in August. Then I bought it again this February. Never a hint of stale gas. ICE runs like a top and get me 60-70 mpg around town and almost that much on trips. 50,000+ miles and counting. I'm hoping for another vacation trip later this year and I'm sure that'll burn a few tanks and greatly increase my average cost per mile.

 

And...several things in that Canadian article don't necessary apply here in the U.S. Don't assume that premium gas is ethanol-free unless a label on the pump says so. The percentage of ethanol will be labeled on the gas pump if it exceeds 10%--stick with E10 max. Ethanol isn't evil--it is the cheapest and least toxic way to increase octane and to oxygenate the gasoline. Agree, it isn't good when stored for long periods of time unless the stabilizer is used. I use nothing but E10, 87 AKI, and have no problems even when it's a couple of months between fill ups.

 

Car gas tanks are vented, but they are in no way open to the atmosphere like gas cans and power equipment are. With those, there is a turn over of the air in the head space with changes in temperature. The gas tank to a lawn mower heats up during the day while sitting in a shed. The air and fuel in the tank expand, pushing vapor laden air out past the gas cap. At night, when things cool down and contract, fresh air gets pulled into the gas tank.

Regulations covering evaporative pollution mean modern cars can't have such turnover of the air in the headspace. So there are systems in place to keep such turn over from happening, and they are monitored for proper operation. That's why the first thing you do with a check engine light is to make sure the gas cap is on correctly, because the computer can tell if it isn't from monitoring the tank pressure.

Since the car isn't leaking gas fumes like a lawnmower, the negative effects from loss of light molecules from evaporation is minimized. With any fumes trapped within the fuel system, there isn't space for more air to come in. The oxygen present will react with something, but then it's done. The level of oxidation is far less when air only gets in when fuel is burned, than when fresh air can find its way in every day.

It is the constant losses to evaporation and oxidation over time that make gas go stale. While vented, car gas tanks are sealed to prevent pollution, which keeps any such losses from being constant over time.

Agreed. Get a BEV if all your daily driving would be in EV mode. Renting a car for those long trips can be a hassle, but people were doing it before plug ins, and then you won't be stressing over the age of the fuel in the tank.

I hope you meant E15, otherwise, checking the gas cap won't turn off the check engine light

 

The Prius is vented to a charcoal canister like most cars are. When the engine is running, the vapors are sucked into the engine to be burned. Toyota Prius P0446: EVAP Vent Control Circuit - Malfunction | Drivetrain Resource

 

The vapor canister and length of the tubing means that there is virtually no turn over of the air and fumes in the headspace of the tank. Without fresh oxygen coming in to react with the fuel, nor fuel vapors escaping the system, the process that degrade the fuel greatly slows down.

https://parts.olathetoyota.com/p0446-code-toyota

In contrast, a lawnmower or other power equipment have a gas cap with a hole in it. When the pressure in the tank builds from expanding air and fumes, a simple valve closes. Before that pressure is reached, some of the fuel vapors will get out. Then fresh air will get in once the vent opens again. With the cap at the top of the tank headspace, there is a regular exchange of old air and fuel vapors with fresh air. It will be worse with an old cap that no longer has a vent that seals. At the other end of the fuel system, the carburetor doesn't even have that simple valve.

Compared to that, car fuel systems are sealed tight. They exist to reduce pollution. If polluted air can't get out, fresh air can't get in. PHEVs might even go further to seal the tank, because of long times between needing fill ups.

 

That is wrong. As the level in the fuel tank drops, the headspace above the gasoline gets replaced with air. That is a sizeable volume.

 

Thanks. Actually, I meant E10. I caught it & fixed it, then read down to your alert notification. I get gas so seldom that I can't remember for sure, but I think E15 is a little uncommon here.

Yes, but that not anywhere near as much as standard tanks that do that plus continuously inhaling and exhaling air as the temperature fluctuates.

 

The fuel drops because it is being burned in the engine. An engine regularly running is going to get fresh gas sooner than a PHEV running mostly in EV mode, but then that PHEV's tank isn't seeing the influx of fresh air. Engines that regularly run only have an issue with stale gas when the gas being supplied is already degraded.

Oxidation is a one way reaction. Once reacted, the oxygen molecule is taken out of circulation. In a car's tank, that means the damage from oxygen is limited as fresh oxygen really only gets in when the fuel level drops. That amount of oxygen isn't going to lead to engine problems before the PHEV's computer tells you it's time to add fresh gas.

The design of power equipment and most gas cans means the fuel will degrade faster than it would in a car.

The main point here is that the equipment on a car's fuel system slows the degradation of gas in it to the point that it is a non-concern for a PHEV that is in service. Those few that can go a year without burning gas, should have gotten a BEV.

I found E15 at Sheetz in the South. Since I only have access to E10 at home, I figured any fuel economy difference would be slight, and it is was around 20 cents cheaper than the E10.

Toyota signed off on E15 for my 2016 Camry. Is that not the case for the current Prius and Prime?