What exactly "contains 10% ethanol" do?

[Paul]

Could it be that 10% weighs less per gallon than straight gas? If so the fuel sender float would have to displace more of it to float, thus making it sink lower in the tank thus giving a lower reading at the gauge.

[sasha055]

I'll keep testing it... at first I thought it was fuel gauge but since it doesn't happen all the time I started to blame ethanol

Pat, before techotorque, I was getting 17MPG on a lucky week, now I'm getting 19.8-20.3, every time I fill the tank I whip the phone and check my MPG, I also changed air filter when I installed technotorque so that might've helped too.

Thanks
Sasha

[pk2]

Typically a higher ethanol percentage gives a false octane reading. 93 oct spiked with ethanol can still give a rating of 93 oct. The diff is, when it "delivers" the heat and how fast.

PK

[landrovered]

The specific gravity of gasoline is .739 and the specific gravity of ethanol is .787, while there is a difference in density of the two liquids, they are not likely to separate unless the car sits for an extended period of time like an entire winter. Movement will keep the two liquids mixed.

The gauge can move at a different rate according to the shape of the fuel tank...due to rounded edges at the top and bottom of the tank or if the tank has an odd shape.

My 986 fuel gauge will go slowly until I get to a quarter tank and then the gauge will drop very quickly to nothing. I fill up at a quarter now and don't like it to drop below a half a tank if I can help it.

[blue2000s]

Originally Posted by pk2

Typically a higher ethanol percentage gives a false octane reading. 93 oct spiked with ethanol can still give a rating of 93 oct. The diff is, when it "delivers" the heat and how fast.

PK

The octane rating is only a measurement of the energy required to combust the air/fuel mixture or activation energy of the mixture. All it does is keep the fuel from igniting off a hot piece of carbon within the combustion chamber before the spark plug fires, preignition. Lower octane fuel takes less energy to light off.

It has nothing to do with the burn rate or energy content of the fuel. Because of the mixture that is typically used to increase octane, it is usually a lower energy content than lower "grade" fuels.

Slower burn rates aren't necessarily a bad thing, by the way.