Explain winter blend gas to me PLEASE

[Jameson]

I have been dropping mpg's to the tune of nearly 15% over the past few weeks, and my habits and style are the same.

Tracked on fuelly I have gone from just over 14 to 12 on the dot since mid october.

I am on Long Island, in NY.

Please explain winter gas and why it hurts mpg. Any good links?


JC

 

[eljefino]

I would worry that any links you find are outdated.

Used to be they added oxygenates to lean out non-feedback carburetors.

Now ethanol is in all the time and there aren't more oxygenates in winter. I believe your car is just wasting gas running rich and cutting through thicker denser colder air, cold wheel bearings, maybe low tires.

Winter blend should have a better Reid Vapor Pressure to evaporate/ light off, but to my knowledge will have the same energy content.

 

[salv]

Summer blends have to meet certain smog standards because the hotter air at the surface traps pollutants closer to the surface.
In the winter, this is not a concern, therefore gasoline is blended with some less expensive chemicals in higher concentrations, like butane. These chemicals burn less efficiently, and can have a negative impact on fuel economy.

Keep in mind that the vehicle remains in "open loop" which is a rich running condition, until the heated O2 sensor reaches a certain temperature. In colder weather it will take longer for the emissions system to attain "closed loop" status, where the ECM will begin metering fuel/air with economy in mind.

 

[Falken]

Salv is bang-on correct

 

[racin4ds]

Also remember that in colder, denser air you are actually using more fuel because your engine is making more power/torque. Oil is thicker on startup, tires are cold and all greases and other fluids are thick.

 

[JHZR2]

Originally Posted By: eljefino
I would worry that any links you find are outdated.

Used to be they added oxygenates to lean out non-feedback carburetors.

Now ethanol is in all the time and there aren't more oxygenates in winter. I believe your car is just wasting gas running rich and cutting through thicker denser colder air, cold wheel bearings, maybe low tires.

Winter blend should have a better Reid Vapor Pressure to evaporate/ light off, but to my knowledge will have the same energy content.


Agreed.

 

[djb]

The answer is that the fuel deliberately has lower energy content.

Why? Because smog reduction goals and standards were set in the 1970s.

The "smog" rules and emissions reduction goals were set using the then-current emissions profile in the formulas. Since the numbers are compared year-over-year, those formulas and tables are pretty much set in stone.

Back then most gas vehicles were carbureted. They were typically tuned to run rich for power, and were very rich with the warm-up choke on. Diluting the fuel was a quick way to dramatically reduce emissions.

Yes, I said dilution. "Oxygenated fuel" isn't an accurate phrase for this change. Burning alcohol doesn't release oxygen. It just uses less oxygen for the volume of fuel, which is related to having a lower energy density.

Today chokes and open-loop engines are vanishingly rare. Changing to a winter gas formula has almost no real-life benefit, and negatives that include a reduction in fuel economy. But that doesn't matter. The formulas say that changing the fuel will reduce emission, and thus it must be done.

 

[badtlc]

Originally Posted By: racin4ds
Also remember that in colder, denser air you are actually using more fuel because your engine is making more power/torque. Oil is thicker on startup, tires are cold and all greases and other fluids are thick.


and air density increases fairly drastically which increases aero drag. this and longer warmup times are the biggest hit to MPGs in cold weather.

 

[cookieman214]

Here is a link to the EPA website: State Winter Oxygenated Fuel Program

http://www.epa.gov/OTAQ/fuels/gasolinefuels/winterprograms/index.htm

 

[NateDN10]

Originally Posted By: racin4ds
Also remember that in colder, denser air you are actually using more fuel because your engine is making more power/torque. Oil is thicker on startup, tires are cold and all greases and other fluids are thick.

The engine is only making more torque if you ask it to by means of the throttle pedal. The ECU takes air temperature into account to achieve the correct AFR.

Other factors are spot-on.

 

[NateDN10]

Warm-up is a big factor too. Engines are most efficient when the block, coolant, and oil are at operational temperatures. Until then, comparatively more energy is being transferred as heat away from the combustion chambers.

 

[NateDN10]

Here's a quote from a 1997 paper referenced in the link cookieman214 provided:
Originally Posted By: EPA
These models consistently show a statistically significant relationship such that, when wintertime oxyfuel is used, the corresponding ambient CO concentrations are reduced by approximately 14 percent on average, with a 95 percent confidence interval of ±4 percent. Considering that the EPA recently estimates that onroad vehicles contribute only 62 percent of total CO emissions, this new analysis indicates that oxyfuels may be reducing mobile CO emissions by as much as 20 percent, a value consistent with recent tunnel data and emissions tests.

 

[440Magnum]

One word: pointless.

Well, it does let refineries get rid of higher-volatility fractions that they normally can't include in gasoline, so it is a bit cheaper.

The original idea was to make "winter blend" fuels evaporate more readily. That's important in carbureted engines, because it improves cold starting, reduces pooling of fuel droplets in the intake, excessive rich running, and all the other warm-up gremlins that carburetors cause. But its of absolutely no use on fuel injected engines. And furthermore, it causes far greater evaporative losses from gasoline station storage tanks, during transport, during fuelling, and even during storage in your car- especially older cars without pressurized vapor-capture fuel systems. Even with a modern fuel system, winter-blend crud can cause the pressure to get high enough to cause the system to vent gasoline vapors, all of which raises ground-level HC and contributes to smog.

Its an idea whose time has passed.... in about 1990.

 

[dparm]

Originally Posted By: salv
Summer blends have to meet certain smog standards because the hotter air at the surface traps pollutants closer to the surface.
In the winter, this is not a concern, therefore gasoline is blended with some less expensive chemicals in higher concentrations, like butane. These chemicals burn less efficiently, and can have a negative impact on fuel economy.

Keep in mind that the vehicle remains in "open loop" which is a rich running condition, until the heated O2 sensor reaches a certain temperature. In colder weather it will take longer for the emissions system to attain "closed loop" status, where the ECM will begin metering fuel/air with economy in mind.



Excellent post. Couldn't have said it better myself.

 

[Vikas]

Wasn't there a topic here talking about how long to warm up your car? May be we should link that one with this so that people might get a clue as to why the mileage goes down.

 

[SOHCman]

Higher vapor pressure helps vehicles start easier, I have noticed this in carbed and FI engines.

 

[Ken2]

Quote:
how long to warm up your car?
Drive it easy as soon as it will drive smoothly. If no warm up time is needed for smooth driving, warm it up by the easy drive. Idling just wastes gas and pukes up the air. An engine heater gives easier starts, saves gas, cleaner air, warm cabin sooner.