June '17

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Page 38 of 83

JUNE 2017 THE SHOP 37 PERFORMANCE ethanol is increased. The fuel efficiency will decrease because gasoline has more energy-per-gallon than the ethanol that is being added to it. The ethanol is added into the gasoline as it is loaded into the delivery tanker truck. It is mixed with the gasoline through a process that is referred to as stop light blending. This process assumes that the ethanol will mix together with the gasoline as the fuel tanker truck stops and starts as it is driven down the road on its way to the gas station to deliver the load of fuel. But sometimes there may be portions of the fuel mixture that have a higher ethanol content than other portions of the same tanker load of fuel. VOLATILITY The volatility of the gasoline is always a concern, because the lighter or more vola- tile portions of gasoline are needed to allow you to start your engine when it is cold. The gasoline that is sold at your corner gas station is blended for summer or winter temperatures. (FYI, winter fuel is more volatile than summer fuel.) A couple of examples would be southern California's summer grade gasoline, which has low volatility to avoid vapor lock, while winter grade gasoline sold in Michigan has high volatility in order to make the engine easier to start in sub-zero temperatures. Reid vapor pressure is basically a mea- surement of the volatility of the gasoline. This measurement indicates how easily the engine is able to convert the liquid gasoline into vaporized gasoline. FUEL VAPORIZATION & VAPOR LOCK Vapor lock (boiling the gasoline in the fuel pump, fuel lines or carburetor) has always been a problem with carburetor- equipped vehicles. The unleaded reformu- lated gasoline of today is blended to allow a modern fuel-injected engine to have the lowest possible exhaust emissions and good fuel economy. These new fuel blends are not really designed for a vintage carburetor-equipped engine that has a mechanical fuel pump and fuel lines that are exposed to high under-hood heat conditions. The carbu- retor is also exposed to a lot of heat and, unlike a set of fuel injectors, the fuel can easily evaporate out of the carburetor through its bowl vents. Vapor lock is not as common on fuel-injected engines, mainly because of the 40 or more pounds of fuel pressure, which raises the boiling point of the fuel. HOW LONG WILL FUEL LIVE IN YOUR TANK? The gasoline sold at your local gas station JUNE 2017 THE SHOP 37 This chart shows the percentage of gasoline that evaporates as the temperature of the fuel increases. This map from Exxon shows the various ar- eas across the nation that require special blends of reformu- lated gasoline. Some states require a label on the gas pump that informs the consumer that the gasoline contains ethanol, but that is not true in every state. This tool from OTC/ Bosch can be used to measure the ethanol content of gasoline.

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