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Old 08-09-2008, 12:02 AM   #1 (permalink)
Stone Axe
Eco Curious
Join Date: Aug 2008
Location: Kentucky
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My New 4cyl Compact Doesn't Get Good Mileage

This is my introductory post.

I just bought a 2006 Suzuki Forenza Wagon with a 2.0l 4 cyl engine. It's only been a couple of days but I can tell that I'm looking at 20-22 mpg in mild city driving! My initial estimates may be colored by the fact that I've idled it a bunch, always ran the AC and only have 60 miles on it.

My previous car was a 1995 Subaru AWD Legacy 5sp with no options. It could get 20 mpg without trying. It had a monster AC that it seemed to know how to switch without significantly impacting power or mileage. It also had a surprising amount of power and torque. I assume that this power helped it overcome the AC and accelerate up to the taller gears to get this mileage.

That era Subaru AWD also had a different transaxle setup than new ones. It had a mechanical 60/40 gearing difference from rear to front and a one-way bearing on the front drive. So the front wheels spun free unless the rear wheels slipped. The new ones are like the Audi's et al and drive both ends and use electronics to split the power via 4 power-robbing torque converters - 1 for the engine (auto trans), 1 for the AWD and 1 each for the differentials. The brain box varies how much each torque converter drags hydraulicaly to distribute power.

I was stunned when I test drove a 2008 Subaru Outback (Legacy Wagon) and found that it actually got worse mileage than my 1995 version - even comparing my 13 yr old one to a 2008 one.

I have had in the past 2 really stunning fuel mileage cars and didn't know what I had when I had them.

The first was a 1979 Mercedes 300SD. It was huge, heavy, overbuilt - the engine block was enormous for a 3.0l and didn't have any material scavenging in the block mold, it looked like it was cut from an iron billet - and had a 3sp auto. The gears were widely spaced but the rear end was geared low to convert it for the American market. In Germany they don't have large city roads and our highway system in the cities - mainly ancient roads built for horses and the rare Autobahn connector. So it was designed to limp through daily city use yet be able to cruise at 100+ mph on the Autobahn. Simply changing the final drive ratio was sufficient to give heartier acceleration and allow for 55-65 mph highway cruise. It got mid 20s in the city and low 30s on the highway!

It was the first car that taught me "eco driving". It was so big and comfortable that it finally dawned on me that there was no point in racing from light to light. It could only do about 100 mph - even though it was a high-end Mercedes when new - due to its gearing, so doing 80+ mph on the highway did not suit it. I described it as my personal city bus, you get in it, take it easy, point it in the direction you wanted to go and let it gently take you there in a civilized manner. Plus it had a ginormous steering wheel that resembled a city bus. What was even more amazing was that it had 250,000 miles on it when I bought it and it maintained this mileage without any abnormal maintenance until I turned 300,000 miles on it and gave it to my nephew who took it to 350,000 miles and drove it to the junkyard!

The next car was a complete surprise. It was a 1985 Nissan Sentra 2dr with literally no options other than AC. It had power nothing, it didn't even have a radio! I was broke and unemployed when I totalled my beloved 1985 BMW 535is 5sp with leather, sunroof and power everything. It got as little as 12mpg and was lucky to break 20mpg on the highway and it needed 91 octane minimum - the owner's manual called for 93 octane! I had just been hired for a high-paying job 60 miles away and probably couldn't even qualify for a "buy here-pay here" car. I walked to an estate sale in my neighborhood and saw this pristine yet homely 1985 Nissan Sentra. I asked how much it cost, it cost $700. I expressed skepticism that any 1985 Nissan was worth more than its scrap weight - $250. The lady told me that it had one owner (her dead dad), full maintenance documentation and only 30,000 miles on it!

I swallowed my pride and went from the "ultimate driving machine" to this 2,000lb "baser than thou" sub-compact with comically tiny and narrow tires. Lo and behold this Sentra was fairly fun to drive and had mind-blowing mileage. I got 46mpg when I was doing 120 mile highway commutes. I still got 36mpg when I switched jobs and had a 20 mile city commute.

This Sentra got me thinking. How and why did it get such great mileage? It tripled the BMW's mileage and doubled the aforementioned Subaru's mileage and had spritely performance. The first thing that came to mind was that it was still a Datsun. It still had Datsun nomenclature everywhere but the trunk lid. Datsun came of age in the 70's gas crisis and this car was the final evolution of that design ethic. Apparently Nissan kept developing fuel mileage technology for several years after it was fashionable. Nissan went on to deny its Datsun heritage to the point that a 2009 Sentra only gets 25/33 mpg and weighs ~3,000 lbs.

Where did they, and everyone else go wrong? Why did my 1985 Sentra get the same kind of mileage as a Prius? Why is the Prius heralded as a technological breakthrough when Nissan could pull similar mileage numbers in 1985 without an ECM, much less a hybrid regenerative drive system? Are we all over thinking this?

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