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2018 GMC Sierra 1500 - Will old gas be a problem?

Just a question in general. With many people’s cars just sitting because of the quarantine going on, is there an issue with gasoline getting old or stale and causing damage to the gas tank or engine? And is there an additive that can be added to avoid any potential damage?

I add this to the tank if gas is going sit for a long time.

Tester

I know our cars are getting driven less, with the sealed systems not so much of a problem. Seafome or techron won’t hurt. I have not done that. Imagine how long some cars sit on the lot, or left mine at the cabins for 2 months, no problem. It is not in my top ten list of concerns.

The system isn’t sealed.

The vent valve in the EVAP system allows the gas tank to vent to the atmosphere.

The only time the vent valve closes is when the EVAP system performs its self test for leaks.

Tester

I stand corrected

First, the EVAP system never releases gas fumes directly to the atmosphere (assuming it’s working correctly.
If the pressure in the tank rises too high (and that would take hot weather) the fumes are released by a relief valve into the activated carbon canister.
Otherwise, the tank is essentially sealed.

In an unsealed tank, like a lawn mower, pressure cannot build, and the more volatile fractions of the gas will evaporate faster.
It’s a slow distillation process.
If this goes on long enough what’s left does not evaporate readily when it’s time to burn in the cylinder: “stale” gas.

In a car’s gas tank, in weather that’s not too hot, gas should be OK for at least 4 months.

2 Likes

I never said the EVAP system allows gas fumes to vent into the atmosphere

The gas fumes are collected by the carbon canister prior to venting the gas tank into the atmosphere.

If the gas tank wasn’t vented into the atmosphere, the gas nozzle would shut off when attempting to refuel the vehicle. As we see so many people complain about on this board.

Also, if the gas tank wasn’t vented into the atmosphere, the gas tank could crack as the gas is drawn from the gas tank.

Car companies have recalls out for spiders that lay egg sacs in the vent hose which can cause a negative pressure in the gas tank, causing the gas tank to crack.

https://www.industryweek.com/operations/quality/article/21963513/suzuki-blames-spider-webs-for-kizashi-sedan-recall

Tester

Yes, definitely.
Even though I barely have anywhere to go, I make it a point to get my car out on the highway for 30-40 minutes, every 5 days or so. That is done primarily for the health of the battery, but it also allows me to see something other than my backyard and the inside of my house.

Even so, I have used only ~ 1/3 of a tank in the past month. I will top-off the tank next week with Top Tier gas, and I think that my rate of consumption will be… okay… for the “health” of the gas in the tank. But, if I wasn’t driving as I do currently, I would put Sta-Bil into the tank to prevent the gas from going bad.