[JimGnitecki]

Obviously, gasoline octane rating is rather important for forced induction engines.

But gasoline octane apparently degrades as gasoline sits in storage in a car's fuel tank.

A 2018 article by a technical specialist at Sunoco Race Fuels says in part:

"87 octane fuels tend to be less refined and contain more unstable hydrocarbons. As the months pass during storage these unstable components react to form gums, varnishes and lower octane hydrocarbons. As a result the octane can decrease within months for 87 octane fuels, especially when stored under less than ideal conditions. 93 octane fuels are more refined and contain more stable hydrocarbons. These stable hydrocarbons can last 2-3 times longer than 87 octane fuel. Even in proper storage 87 octane gas can start to degrade in 3 months, 93 octane fuel should last closer to 9 months before degradation is noticeable. Keep in mind that 93 octane fuels are still susceptible to octane loss and vapor pressure decreases due to butane evaporation."

Here in the Province of Alberta, in Canada, we had an unusually (record even) cold, icy, and road-salted time period in November and December, that made driving my Magnuson supercharged LT1 impractical. So, basically, my Camaro has not been driven, except twice for a few kilometers each time, since Halloween, 2-1/2 months ago. The car was last refueled with 91 octane gasoline (the highest octane locally available) around Halloween.

I realize that the Sunoco tech article seems to say that high octane fuel MIGHT not degrade for as long as 9 months. But am I correct in thinking that when the current persistent icy period ends, it might be unwise to use a lot of throttle until the "old" gas in the tank gets used up and replaced by new fuel? Or, is there a safe additive that can be added to the tank to alleviate any octane concerns?

For what it's worth, the car has been stored in a garage where temperature has been relatively stable, most of the time remaining at about 8 degrees C = 46 degrees F, but once getting as low as +2C = 36F when the temperature outside hit -32C = -26F!

Jim G

[ZO6Ted]

I use a product in my lawn equipment called Stabil. It last's up to 2 yrs and keeps the gas usable. I would reach out to them to ask about your vehicle use though as well as your tuner.

[ctrlz]

I think this is the article you are referencing:
https://petroleumservicecompany.com/...-octane-fuels/

Over a period of a few months, with gas in the car's tank, I would not worry much about this. The bit about butane is referring to the reid vapor index, I believe, which refineries tune according to the season. Your winter fuel may lose butane, but you will get some vapor pressure back with warmer ambient temps.

If fuel has been sitting in the car for awhile, I would basically drive it, but not push it, until after a few refuelings.

[cheeze9878]

I wouldn't worry about it at all. I'm in Michigan and my car sits from Nov. 14 (the day before opening day for rifle hunting) until the first good rain after snow stopped falling to wash away the salt (March-April). I get in go to the gas station put in one can of "Sea Foam Motor Treatment" before filling up so that filling up mixes it really good into the gas and drive it like normal. You may see a small amount of white smoke from the exhaust for the first tank ( its cleaning out carbon build up) and that's it.

[ZO6Ted]

Could Seafoam be good once in a while anyway since we are DI? If so for carbon buildup I'm doing it.

[cheeze9878]

Originally Posted by ZO6Ted

Could Seafoam be good once in a while anyway since we are DI? If so for carbon buildup I'm doing it.

I do it twice a summer, once when I bring the car out and once in end of Sept beginning of Oct.


All depends on how much or how little you drive it really.

[302crossram]

Originally Posted by ZO6Ted

Could Seafoam be good once in a while anyway since we are DI? If so for carbon buildup I'm doing it.

far superior to Seafoam..

[RamAir02]

Originally Posted by ZO6Ted

Could Seafoam be good once in a while anyway since we are DI? If so for carbon buildup I'm doing it.

I've seen a few videos where folks run Seafoam or some other cleaner through the intake, then use an endoscope to take a look at the intake valves. In each case, there has been marginal to no improvement in the amount of buildup. I think the only real way to clean that up is either walnut blasting or manual cleanup with a wire brush. Important to ensure the valves are closed when cleaning to avoid any crud falling into the cylinders.

[GXP08jrf]

For reference:

Last Spring I decided to get my '97 registered for the road after several years of "storage". It was throwing mis-fire codes when cold and I wasn't looking forward to changing the optispark distributor, which I assumed was the problem. So I ignored the cold mis-fires because other wise the car seemed to run well when warm. It'd been doing this for the past few years, and was part of the reason it wasn't registered: I didn't want to strand myself driving around.

I never used addatives or made sure the tank was at any particular level. Simply park it (in un-heated pole barn in Michigan), and don't worry about it.

So when I did get it registered this Spring, the mis-fire was annoying, but was completely gone by the Fall, and I wan't sure exactly why until I was putting that vehicle's maintenance records into a spreadsheet In October and discovered I hadn't filled that car at a gas station in over a decade! Just would splash from a can now and then. So after running the tank to near empty a couple of times and fresh "kroger" premium, the vehicle doesn't skip a beat.

So I determined that the gas was likely the root of my problem, because the car now runs like new (32,000 on the odo.), with almost no attention given to maintenance as far as fueling goes.

Now I don't recommend decade intervals for regular maintenance, and maybe I'm lucky (This would be a first), but even if some degredation occurs, the closed system in most modern automobiles is likely sufficient enough to keep fuel "fresh enough" for a few months if not a couple of years.

Don't worry about it.

[JimGnitecki]

Originally Posted by GXP08jrf

For reference:

. . .

Don't worry about it.

The reason I worry about it is the Magnuson supercharger kit, on an LT1 engine, supercharges an engine that already has a pretty high compression ratio, which means the octane rating should be as high as practical.

In addition, with the OEM tires, which I had on the car until my Nitto 555R2 drag radials came in just after this awful weather began, traction was pretty marginal - the ECM triggered traction control anytime the throttle was floored at least through 85 mph. IF stale fuel triggers any hiccups in power delivery at a high throttle opening, on cold low-friction pavement, that could be quite bad.

Hence my thought that more modest throttle openings might be a good idea until I get fresh fuel into the tank.

Jim G

[asthmamax11]

Keep some Boostane around

[KingLT1]

Lucas Ethanol fuel treatment and stabilizer. Works great for all fuels from E10 to E85.

[Jus Cruisin]

The gas tank isn't that big. Just drive it like a sane person for a couple hundred miles..... Not that hard. I have Stabil in my tank that has been sitting since the end of October and it'll not move until April.

[JimGnitecki]

Originally Posted by KingLT1

Lucas Ethanol fuel treatment and stabilizer. Works great for all fuels from E10 to E85.

Does using Lucas Ethanol fuel treatment and stabilizer, or Stabil, have any adverse effects at all on a supercharged engine?

Jim G