I never put more than half a tank of e85 at a time in my 1989 Oldsmobile Cutlass supreme, and I only add it once a week. Corrossivity is only an issue if it's contaminated with water, the real nuisance is that the sensors detect a change in oxygen content and would set off the check engine light if you used more than half a tank of e85 at a time for an extended period. Thus once a week less than half a tank is minimal hassle while still saving money since e85 is 55 cents cheaper and widely available here. When diluted in this fashion e85 just acts as a volume extender for gasoline and has very little effect on gas mileage. If you bother to measure your mileage and volume added you should post your results for our education.
This is direct from the relevent wikipedia article:
"E85 has a considerably higher octane rating than gasoline ? about 110 ? a difference significant enough that it does not burn as efficiently in traditionally-manufactured internal-combustion engines.
Use of E85 in non-FFV vehicles is generally experimental, with some users recommending light blends as low as 20%, while others have successfully run 100% E85. The main attraction of burning E85, of course, is the lower price per gallon at the pump of E85 versus gasoline. Other advantages include the common benefits of renewable energy sources, such as less environmental impact and less reliance on foreign energy.
Modern cars (i.e., most cars built after 1988) have fuel-injection engines with oxygen sensors that will attempt to adjust the air-fuel mixture for the extra oxygenation of E85, with variable effects on performance. All such cars can burn small amounts of E85 with no ill effects.
Operating fuel-injected non-FFVs on more than 50% E85 will generally cause the check engine light (CEL) to illuminate, indicating that the ECU can no longer maintain closed-loop control of the internal combustion process due to the presence of more oxygen in E85 than in gasoline. Once the CEL illuminates, adding more E85 to the fuel tank becomes rather inefficient. For example, running 90% E85 in a non-FFV will reduce fuel economy by 33% or more relative to what would be achieved running 100% gasoline. (This example is illustrated above in the previous section - the 1998 Chevy S10 pickup experiment.) Even more importantly, continuing to operate the non-FFV with the check engine light (CEL) illuminated may also cause damage to the catalytic converter as well as to the engine pistons if allowed to persist. To run a non-FFV with amounts of E85 high enough to cause the CEL to illuminate risks severe damage to the vehicle, that may outweigh any economic benefit of E85.
Under stoichiometric combustion conditions, ideal combustion occurs for burning pure gasoline as well as for various mixes of gasoline and E85 (at least until the CEL illuminates in the non-FFV) such that there is no significant amount of uncombined oxygen or unburned fuel being emitted in the exhaust. This means that no change in the exhaust manifold oxygen sensor is required for either FFVs or non-FFVs when burning higher percentages of E85. This also means that the catalytic converter on the non-FFV burning E85 mixed with gasoline is not being stressed by the presence of too much oxygen in the exhaust, which would otherwise reduce catalytic converter operating life.
Nonetheless, even when the CEL does not illuminate on the non-FFV burning E85, proper catalytic operation of the catalytic converter for a non-FFV burning higher percentages of E85 may not be achieved as soon as necessary to prevent the emission of some pollution products resulting from burning the gasoline contained in the mixture, especially upon initial cold engine start. This is because the catalytic converter needs to rise to an internal temperature of approximately 300 degrees C before it can 'fire off' and commence its intended catalytic function operation. When burning large amounts of E85 in a non-FFV, the cooler burning characteristics of alcohol fuel than gasoline fuel may delay reaching the 'fire-off' temperature in a non-FFV as quickly as when burning gasoline. Any additional pollution, however, is only going to be emitted for a very short distance when burning E85 in a non-FFV, as the catalytic converter will nonetheless still 'fire off' quite quickly and commence catalytic operation shortly. It is not known whether the small amount of pollution emitted prior to catalytic converter 'fire off' may actually be reduced even during the cold startup phase, as well as once catalytic operation commences, when burning E85 in a non-FFV. Likewise, even once the catalytic converter 'fires off', operation with the CEL illuminated will still result in excess amounts of nitrous oxide being released, greater than when operating the engine on gasoline. The solution is simply to add gasoline, and extinguish the check engine light (CEL), at which time exhaust pollutants will return to within normal limits .
For non-FFVs burning E85 once the CEL illuminates, it is the lessened amount of fuel injection than what is needed that causes the air fuel mixture to become too lean; that is, there is not enough fuel being injected into the combustion process, with the result that the oxygen content in the exhaust rises out of limits, and perfect (i.e., stoichiometric) combustion is lost if the percentage of E85 in the fuel tank becomes too high. It is the loss of near-stoichiometric combustion that causes the excessive loss of fuel economy in non-FFVs burning too high a percentage of E85 versus gasoline in their fuel mix.
E85 gives particularly good results in turbocharged cars due to its high octane [2]. It allows the ECU to run more favorable ignition timing and leaner fuel mixtures than are possible on normal premium gasoline. Users who have experimented with converting OBDII (i.e., On-Board Diagnostic System 2, that is for 1996 model year and later) turbocharged cars to run on E85 have had very good results. Experiments indicate that most OBDII-specification turbocharged cars can run up to approximately 39% E85 (33% ethanol) with no CEL's or other problems. (In contrast, most OBDII specification fuel-injected non-turbocharged cars and light trucks are more forgiving and can usually operate well with in excess of 50% E85 (42% ethanol) prior to having CEL's occur.) Fuel system compatibility issues have not been reported for any OBDII cars or light trucks running on high ethanol mixes of E85 and gasoline for periods of time exceeding two years. (This is likely to be the outcome justifiably expected of the normal conservative automotive engineer's predisposition not to design a fuel system merely resistant to ethanol in E10, or 10% percentages, but instead to select materials for the fuel system that are nearly impervious to ethanol.)
Fuel economy does not drop as much as might be expected in turbocharged engines based on the specific energy content of E85 compared to gasoline, in contrast to the previously-reported reduction of 23.7% reduction in a 60:40 blend of gasoline to E85 for one non-turbocharged, fuel-injected, non-FFV. Although E85 contains only 72% of the energy on a gallon for gallon basis compared to gasoline, experimenters have seen much better fuel mileage than this difference in energy content implies. Many automotive writers and columnists suggest that because of the lower energy content, you should expect an equivalent 39% increase in fuel usage. This has not been observed in practice when running gasoline and ethanol blends. Some of the newest model FFV's get only about 7% less mileage per gallon of fuel of E85 compared to their gasoline fuel mileage."
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