Our local gas stations are changing over from the summer blend of fuel to the winter blend. What is the difference? Does the car run better on one than it does on the other? I know summer blend is supposed to help reduce air pollution. Are there any other effects?


Thanks,

Jim

 

There is a vapor index that measures the volatility of the gasoline or how much boils off into the atmosphere because of temperature and pressure. Winter gasoline can have a slightly cheaper blend where there is less concern of butane and other components vaporizing.

Should make no difference in a modern auto.

 

I could be wrong, but I don't think the fact that the blend may be cheaper to produce is the key. My understanding is that winter blends are typically a little more volital to help with cold weather starting.

 

It may be that at some time or in some areas volatility was changed to aid the consumer, but as far as I know the reason for changes are mandated by the EPA and has to do with evaporative emissions. The change is actually made in the summer and the volatility by area is outlined in this document: http://www.epa.gov/otaq/regs/fuels/420b05012.pdf

Winter gasoline is actually the 'normal' configuration so I probably should have just said summer gasoline is more expensive to produce.

 

OK. I understand the reason the EPA requires the summer blends in many areas. The question is does one blend have any advantage over the other performance wise? I suspect most cars would perform better on the winter blend.....IF you can keep all of the components from boiling out of the mix. Anyone Know?

 

a car in the winter which normally uses mid grade would work well on a lower grade?

 

There is no performance impact with these gasoline variations. Your car will probably run better in the winter because the air is cooler.