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13 January 2008 @ 12:38 pm
Summer/winter gas  
Has anyone ever had a problem with a car (or heard of a direct friend) that didn't get driven much that had the wrong season's gas in it? I've heard that in extreme cases it can cause starting problems, but perhaps the Boston formulas aren't that extreme?
Deneb: teslaalphacygni on January 13th, 2008 06:29 pm (UTC)
I've never heard of this, actually. Gas has seasonal variations? But my car isn't driven much, and has probably been in this situation on the seasonal borders at least once, and I've never had a problem with it starting.
Someone I am is waiting for my courageforgotten_aria on January 13th, 2008 06:36 pm (UTC)
From wikipedia: In cold climates, too little volatility results in cars failing to start. In hot climates, excessive volatility results in what is known as "vapour lock" where combustion fails to occur, because the liquid fuel has changed to a gaseous fuel in the fuel lines.

In the United States, volatility is regulated in large urban centers to reduce the emission of unburned hydrocarbons. In large cities, so-called reformulated gasoline that is less prone to evaporation, among other properties, is required. In Australia summer petrol volatility limits are set by State Governments and vary between capital cities. Most countries simply have a summer, winter and perhaps intermediate limit.
Jeredjered on January 13th, 2008 10:09 pm (UTC)
What she said. Basically, in the winter they add up to 10% ethanol to the fuel to add oxygen (increasing combustion efficiency) and increase volatility. This also has the effect of reducing mileage -- yet strangely you don't get a discount in the winter for the fact that they're given you less petroleum...

And to answer the original question, maskin77 says that the winter gas in summer vapor lock issue does occur, but he hasn't heard of it happening with a modern car.
Jacob: tankkvarko on January 13th, 2008 07:23 pm (UTC)
I've never heard of seasonal gas either :)

I have heard of putting different oil in during winter, using something less dense for winter like WD30 instead of WD40. The place I get my regular maintenance uses WD30 year-round, though.
Gergzkzkz on January 14th, 2008 12:04 pm (UTC)
This is a real problem for diesel. In cold weather disel gums up, basically turning into wax. You can buy disel fuel winter additive if you have summer disel in the tank when winter comes along. Normally it doesn't happen unless you drive very rarely, though there are reports that some of the VW TDIs get such good mileage that you can run into the problem driving up from, say, Atlanta to Boston on a single tank of gas...

I hadn't heard of it for gasoline though. If Jered's right about it being a different percentage of oxygenate then I would expect the first symptom would be knocking. Most engines have variable timing anyways so that wouldn't really happen, you would just lose a little power and fuel efficiency.
Binkbinkbink on January 18th, 2008 07:30 pm (UTC)
Winter gas in summer may emit excess emissions and cause your car to fail to comply with regulations, but it shouldn't be that much harder to start on a hot day. Vapour lock is now a rare thing with modern fuel delivery systems, fuel injectors, and pollution scavengers.

Summer gas in winter isn't likely to be a problem unless the day is very (painfully) cold.
You are more likely to have your washer fluid turn to slush on a day like that.

The big concern is how long the gas is in the tank.
Older gas loses its light ends and makes starting harder.

Cat: it would be in the tank about twice as long as it now, which is maybe... a month or two.
- Not too much of a problem. Maybe on a really cold day you will have a hard start, but I don't think you should consider it an issue.

Though it did take a bit more cranking, I have managed a cold start on gas that was over a year old. On the other hand, I will need to replace the fuel in the De Lorean before attempting to start it even on a warm day.

And of course you already know not to get high octane (which is more stable) unless your car specs require it or the engine is knocking.

If you are worried about summer gas in winter, there is one more option. After the heat of summer is past, you can fill up at Sunoco on the sub-regular grade they offer.