Mahout, you are 100% spot on. I could not agree with everything in you post any more than I do. Good posting.

 

I agree for the most part, but it not the cylinder walls its the bearings and lack of protection. Plateau honed cylinders by definition is already broken in pattern and Ion pistons rings is a coated or harden ring. I agree with a rebuilt where you honed the cylinders is different. I agree about the first 100 mile ride is the best for the engine but its because the heat is controlled and the cam,engine bearing get a constant supply of oil to form its protection and the fuel and timing trims are formed too. Its all about controlling heat on the new parts. Better mpg is because of fuel trim refined and the lubrication protection on the bearings combined with the added compression from carbon buildup.

 

month/year..............ave miles per gallon
november 2008.............31.5
november 2009.............31.8
november 2010.............31.2

 

A major problem with your mpg reports is that you can't be sure the gasoline you were burning was the same. We know there has been a reduction in btu per gallon over the past few years as refiners try to increase output to keep up with demand.Typical reported energy loss 114,000 btu to 112,000 btu. That alone would make your range from 31.8 to 31.2 mpg. And how much did the driving differ per tank?
Worse, did you do a statistical measurement, averaging say 10 tankfuls in each year at the same time oif year and driving style and range, finding a standard deviation, and then doing a 95% level of significance determination that any of the 3 are realkly different ?
Its not a simple comparison of one tank vs another in the real world.

I've done the analysis here and my year to year in 4 cars shows only a small decrease in mpg is significant, about a quarter of an mpg. I blame it entirely on the energy decrease in the gasoline, all from the same brand and station. In the past I have done the same with new cars immediately after break-in compared to a year later and found a 2-3% increase in mpg.
(mpg during break-in was always higher than normal because of the easy going driving.)
cheers.

 

Carbon builds up from knock the higher temps causes the carbon to stick to head,valves and underneath the piston by the oil and causes hot spots. The detergents help but it also causes the cat. to overheat and also stress the emission system. 87 octane has no knock with a 8 to 1 and with the 10.4 compression of the fit it can still knock with 93. The knock sensor and the oil sprayed help control the heat but it still knocks lowering efficiency if the wrong fuel is used. I agree with you about lower btus in gasoline and getting worse.

 

Mahout, this is what I was saying about the BMW unlimited test and BP

http://www.fuelcertification.com/doc..._Additives.pdf
http://www.government-fleet.com/fc_r...el-history.pdf for the history