| [GMCnet] Summer vs winter gas, simple explanation [message #318367] |
Fri, 02 June 2017 09:38  |
glwgmc
Messages: 1014
Registered: June 2004
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The following came from a Rock Auto news letter and offers a simple explanation as to the differences between winter and summer gas and carb vs EFI.
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I recently took my '71 Ford LTD out for a drive. With "summer-blend" gasoline I bought last fall in the fuel tank and cool weather, the engine ran great. I enjoyed that instant throttle response that makes a carbureted motor so much fun to drive. Last summer, the Ford's carburetor and I were less happy when some "winter-blend" gas, coupled with hot weather and traffic, led to vapor lock induced hesitation and stalling. Rolling to a stop on the edge of a freeway cloverleaf was disconcerting. The engine ran OK once the engine compartment cooled down and the traffic cleared.
Vapor lock happens when gasoline gets too warm and evaporates before it makes it into the engine. Fuel injected engines rarely experience vapor lock because an electric fuel pump submerged in the fuel tank keeps the gasoline under high pressure. Carburetor based fuel systems typically use a low pressure mechanical fuel pump mounted on the engine. Without much pressure, it is easier for gasoline to prematurely vaporize in a hot fuel line, fuel pump or carburetor. The fuel pump cannot pump vapor and the engine stalls.
Vapor pressure is a measure of how eager gasoline is to evaporate. Winter-blend gasoline has higher vapor pressure. Higher vapor pressure makes an engine easier to start in cold weather because the fuel vaporizes more readily inside cold cylinders. Winter-blend gas costs less because it contains more inexpensive volatile hydrocarbons such as butane. (Butane is an ingredient in some aerosol cans of "starting fluid" used to help start balky cold engines.)
Summer-blend gasoline has lower vapor pressure and costs more. It is less likely to cause vapor lock in a fuel system or evaporate and contribute to air pollution. My '71 Ford is safely swaddled in the garage during the coldest part of the winter. Today's summer-blend gasoline is the closest thing to the low vapor pressure gasoline blends sold in the 1960s. After my vapor lock experience last year, I try to keep summer-blend gasoline in my '71 Ford's tank as much as possible.
The availability and composition of summer/winter blends varies depending on the local climate. Regions with mild weather and relatively little air pollution might not bother to switch blends seasonally. In those areas, something similar to a winter-blend is usually the default gasoline because of its lower cost. Most newer cars can work OK with winter blend gasoline year-round because their high pressure fuel pumps prevent vapor lock and their sealed fuel systems prevent air pollution. Vapor Canister Purge Valves, Vapor Canister Vent Valves and other EVAP system parts (listed under "Exhaust and Emission" in the catalog) help catch and condense any evaporated gasoline.
It may seem counterintuitive, but when the weather heats up, a larger city with stricter air pollution regulations may be the place to find the best gasoline (summer-blend) for your old carbureted cars/trucks.
Tom Taylor,
RockAuto.com”
Jerry
Jerry Work
The Dovetail Joint
Fine furniture designed and hand crafted in the 1907 former Masonic Temple building in historic Kerby, OR
glwork@mac.com
http://jerrywork.com
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Jerry & Sharon Work
78 Royale
Kerby, OR
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