What exactly "contains 10% ethanol" do? - 986 Forum - The Community for Porsche Boxster & Cayman Owners

sasha055 · 09-09-2011, 02:35 PM

Hi,

After installing Pedro's technotorque I started watching more closely my MPG and I noticed an interesting trend.

Normally I make around 20MPG (up from 16-17 before technotorque),
however I noticed that if I use gas with ethanol, sometimes first half of quarter is gone in 10 miles, after that it's the normal 80 miles per quarter of tank.

This never happens when I fill in with pure gas (extremely hard to find here in Seattle), and sometimes even if I fill gas with ethanol it behaves normaly..

So I'm thinking that "contains 10% ethanol" might fill my tank with more ethanol (it's not like it's mixed perfectly at the station) and if this happens my mileage for the first 10-15 miles sucks, after ethanol is gone .. it goes back to normal.

Am I paranoid?

Thanks
Sasha

landrovered · 09-09-2011, 03:04 PM

First...ethanol does not contain as many calories as gasoline so you will see a reduction in MPG when ethanol is added. Burning of one kilogram of gasoline produces about 10500 kilocalories. Burning one kilogram of ethanol produces about 7140 kilocalories.

If the fuel is 10% ethanol then the reduction will be minimal, a 4% reduction in calories by my calculations.

The problem is when the mix is not 10% then you can see a drop in performance.

Pat · 09-09-2011, 07:20 PM

There's no way the technotorque mod got you three to four MPG. It's just not going to happen.

WhipE350 · 09-09-2011, 07:31 PM

I know when I fill my Boxster the first 1/4 tank goes really fast, it is just the gauge I'm guessing since I have had other cars that do this. It sounds like what your describing is some type of separation of the ethanol and gas with the ethanol being pulled to the engine first. I have no idea if this is possible, it's not like you are mixing water and gas. I know my old 2007 MB C230 ran that E85 and it was as expected about 30% less efficient.

Not paranoid...just do some test runs. Fill it up, drive 100 miles and fill it up again...see what your mpg is. do the same with a whole tang full, I think you'll find they are pretty close to the same...if not...ya something strange is happening.

Paul · 09-09-2011, 08:06 PM

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 · 09-10-2011, 06:13 AM

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

blue2000s · 09-10-2011, 02:47 PM

Quote:

Originally Posted by sasha055

Hi,

After installing Pedro's technotorque I started watching more closely my MPG and I noticed an interesting trend.

Normally I make around 20MPG (up from 16-17 before technotorque),
however I noticed that if I use gas with ethanol, sometimes first half of quarter is gone in 10 miles, after that it's the normal 80 miles per quarter of tank.

This never happens when I fill in with pure gas (extremely hard to find here in Seattle), and sometimes even if I fill gas with ethanol it behaves normaly..

So I'm thinking that "contains 10% ethanol" might fill my tank with more ethanol (it's not like it's mixed perfectly at the station) and if this happens my mileage for the first 10-15 miles sucks, after ethanol is gone .. it goes back to normal.

Am I paranoid?

Thanks
Sasha

The ethanol won't separate out and your car would't run if it did.

You must be driving uphill for the first 1/4 tank.

landrovered · 09-10-2011, 03:03 PM

Ethanol is added to gasoline as an oxygenate to reduce emissions not to increase octane. Ethanol replaced MTBE as the oxygenate of choice due to MTBEs ability to have a small amount of MTBE contaminate a very large amount of drinking water.

Octane as previously mentioned is actually added to make the gas/air mixture harder to ignite so. It does not increase the caloric content of gasoline, it actually decreases it. Octane is control not power. Power comes from a properly timed and near stochiometric combustion process and that requires control to achieve.

blue2000s · 09-10-2011, 03:10 PM

Quote:

Originally Posted by landrovered

Ethanol is added to gasoline as an oxygenate to reduce emissions not to increase octane. Ethanol replaced MTBE as the oxygenate of choice due to MTBEs ability to have a small amount of MTBE contaminate a very large amount of drinking water.

Octane as previously mentioned is actually added to make the gas/air mixture harder to ignite so. It does not increase the caloric content of gasoline, it actually decreases it. Octane is control not power. Power comes from a properly timed and near stochiometric combustion process and that requires control to achieve.

Ethanol does increase the octane level of gasoline. That's not the reason for it's inclusion, but it is an effect.

Power comes from complete combustion of a high energy content fuel. Stoichiometric is usually too lean for maximum power in practice.

landrovered · 09-10-2011, 03:19 PM

Sure ethanol increases octane just like JP-5 but that was my point...it is not the octane additive that you are getting when you pay extra for 92 unleaded. That increase comes from isooctane and toluene.

I did say near stochiometric, I know that many engine manufacturers run their fuel curves very rich to cool the fuel/air mixture to reduce knocking and also to insure complete combustion in the catalytic converter but that really just reduces overall efficiency and of course too lean under load makes for hot spots and can cause cracked heads and all sorts of other problems. It is a Goldilocks deal.

WhipE350 · 09-10-2011, 05:32 PM

blue2000s, landrovered, Thanks for the very informative discussion, heck with searching Yahoo or Google you just explained a lot.

Question, what do high performance and luxury cars gain by using higher octane at the simplest level. I understand the delayed combustion but why is that important to the manufactures? Does it allow these cars to run at higher rpm's and not experience pre-ignition thus controlling energy output?

Thanks guys.

brp987 · 09-10-2011, 06:01 PM

What does 10% ethanol do? It causes you to pay more to drive a shorter distance.

The purported justification for the use of ethanol in that reduces reliance on petroleum is not true. While it may be true that ethanol/MTBE can function as oxygenates, they are unnecessary to achieve current emissions standards. While high compression engines require high octane fuels, it still does not justify the use of ethanol. Politics, nothing but politics.