How to properly test modifications (AKA: don't believe every MPG claim you read)

[Nerys]

ahh I understand. warming up gets you a lot lower fuel economy DURING the warm up. so a shorter trip means that warm up period is much larger percentage wise so the colder temps will hit this "warm up" period more and since its a larger percentage of your total trip the effect is visible in the numbers. So I won't see as much a gain if any from a engine heater on my FE as for example he might?

[PaleMelanesian]

I think that's a big factor here. With 10 miles, a cool-running engine, and lots of low-speed and EOC driving, my entire drive is the warmup period.

[SentraSE-R]

Yes. I drove my wife's car to Las Vegas from the Bay Area last month, and gassed up when we got there. That night, we drove to another part of town to see a show. The next day, I drove home. The night I drove to the casino, I put 13 miles on the car at 17 mpg. It took me the next 450 miles to bring my mileage up over 40 mpg the next day, because I'd used nearly a full gallon to go 13 miles on a cold engine in city conditions.

[Nerys]

A GALLON IN THIRTEEN MILES!! what kind of car uses a gallon in 13 miles warming up but gets WELL over 40mpg normally?

even my 5 liter 5500 pound van does not use a gallon in 13 miles (unless I get 10-11% ethanol :-) hehe

[SentraSE-R]

You name me a car capable of getting 40 mpg, and I'll show you how to get 13 (actually 17) mpg out of it.

The car I did it with is my wife's '06 AT Hyundai Elantra. We drove at night, had to run the heater and lights, and didn't hit many stoplights on green. We also had to drive the Strip on a weekend, with its stop and go traffic. Even FASing at lights, I could only get 17 mpg that night.

When I lived in Alaska, I could only expect 5 mpg in the winter with my 4X4 Scout. Winter driving kills fuel economy.

I actually averaged >41 mpg over ~1000 miles on that trip. It just took all day to overcome the effects of that first 13 miles at 17 mpg. When you're doing short commutes every day, you never overcome the cold starts.

[Old Tele man]

...sometimes it's NOT your milage that's so bad, but rather all the unwelcomed HELP you get from other drivers, stop lights and grid-lock traffic.

[Nerys]

wow - even with bad parts clogged egr etc... I never got under 42mpg in my metro. My van never saw less than 13mpg even towing a 7000 pound trailer on Ethanol with the AC on!!

I just did not think it was possible under normal conditions to have such a massive swing in FE in a vehicle short of massive issues with the car.

I was just shocked is all :-)

well actually I don't think you CAN get 13mpg in that car. maybe 13mpg INSTANT reading maybe but average even over a few miles I don't think you can get 13mpg without REALLY hammering it or something.

I forgot you have a computer read out of your FE as you drive :-)

[SentraSE-R]

That was trip and tank average fuel economy for the 13 miles. It's not uncommon for an AT econocar to stay under 20 mpg for the first few miles when it's started up. My wife's car doesn't have a fe readout. I had a Scangauge plugged into it.

[Nerys]

yeah I know Scangauge was your FE read out :-)

[MetroMPG]

well actually I don't think you CAN get 13mpg in that car. maybe 13mpg INSTANT reading maybe

Darrell's point is that he is telling you that 13 mpg was an average reading, not just some random "instant" MPG value, as suggested.

Nerys: careful about insisting so strongly that people must be wrong. Your experience isn't everyone's experience. Lots to learn from the members here.