13 mpg decrease after mods possible or most likely just a mistake?

[AaronMartinSole]

I'm sure it's just a mistake but I can't ever recall ever incorrectly setting my trip meter or messing up the gallon count. But if it's impossible then I must've been wrong.

I guess I may or may not have gotten a 39 mpg count on this 2001 Corolla. This car had been sitting in a garage for months and did not start. Added water to the battery and jump-started it. This is the first time I have ever driven this car and I knew nothing about it. The only thing I did was put some fuel injector cleaner in the gas tank, put about 50-100 miles on it for the car to gather data for a smog test, got the gas tank almost down to a tenth, and then filled it back up. The tires were almost flat, I mean 20 psi. Filled it up full. I kept the tires under-inflated, probably to just cheat myself into a more satisfying mpg increase, slanderous and pathetic, I know- I reset the trip counter, then ran a hundred or so miles and swear I recorded a 39 mpg reading. No modifications other than adding fuel injector cleaner in the gas tank. Mostly highway miles on this run. I refilled at Chevron instead of the other cheaper place I usually go to, out of convenience. Maybe there was a mistake with the gas pump?

Both times I drove with the front driver and passenger windows all the way down, every second of driving, even on the highway. Now I know that seems like sacrilege, but I value fresh air and my health more than a few points of mpg, though I have been known to drive with only the sunroof cracked on the highway, with the A/C off, sweating my brains out, in order to increase mileage. But it's just too hot now. Now people say they believe in fresh air, but I really believe in fresh air- like open windows day and night, summer and winter, no a/c or heat ever sort of believe in fresh air. There are stories of indoor air quality and mold and freon and so on. You wouldn't believe the health benefits and the chronic sicknesses people have that would just disappear if they but just cracked open a few windows and let some purifying sunlight into the house. But nevertheless,

Then I replaced the spark plugs with Iridium ones. I drained out the old oil which I believe was 10W-something Castrol judging by the sticker. I put in an engine flush and put in AMSOIL 0W-20 Synthetic Signature Series. I also put the P.I. fuel cleaner from AMSOIL as well. Drained out the old coolant and put in a coolant flush with distilled water and ran around with that for a couple days. I pumped up the tires. Ran a hundred miles or so and got 26 mpg.

Now one thing to note - that supposed 39 mpg run was mostly highway. This 26 mpg run was mostly city. But still, shouldn't be that large a discrepancy right? Maybe I just got that first reading wrong but I'm 80% sure I didn't. Now I did idle on both runs for a maximum of 25 minutes for the coolant flushing and filling. So I figured it would sort of even out. A lot of weird variables I know, let's just see how this next tank goes.

I'm not really familiar with all this so I suppose I'm wondering if- and that's an if- if the first run really was 39 mpg and my second run after maintenance really was 26 mpg, what could the possible reasons be for such a decrease in mileage? If anything, it should've increased, right? Am I crazy???

[Frank Lee]

Yes.

[AaronMartinSole]

Originally Posted by Frank Lee

Yes.

. Now that I look at it, fueleconomy.gov says this about the 2001 automatic Corolla:

26
City
30
Combined
36
Highway

That's for the 4-speed and there's a 3-speed as well, along with a manual version. How do I know if mine is a 4 or a 3 speed? But back to the main issue, according to this, a 2001 Corolla is supposed to get 26 mpg city, which is what I recorded, and 36 mpg highway, in which I recorded a 39 mpg run which was mostly highway. So... yeah. But come on, that's a big gap between city and highway, right? ...right? I wasn't overreacting guys! Why would there be such a huge gap? WHY? But could anything that I did to the car have affected the mileage and in which way would it have affected it - increasing mpg or decreasing? Surely 0W-20 should increase mileage, right? Car's got 100,000 miles on it if it matters, and it feels like it's been through better days.

[2000mc]

maybe get a baseline of your mileage before getting too worked up

i could make my car get anywhere between 0 and 50 mpg depending on how i drove it, ive had tanks from 16mpg all very short trips in pittsburgh in the winter, to 45mpg with an easy commute

[AaronMartinSole]

Originally Posted by 2000mc

maybe get a baseline of your mileage before getting too worked up

i could make my car get anywhere between 0 and 50 mpg depending on how i drove it, ive had tanks from 16mpg all very short trips in pittsburgh in the winter, to 45mpg with an easy commute

I suppose it's normal for everyone's mpg to decrease in the winter? What do you do in the winter - anything different?

[2000mc]

i've moved around the last couple years, different driving situations, usually when i get my worst mileage i spend the least on fuel because i'm not going very far. i'm just saying there was nothing wrong with the car. start a fuel log and keep notes so you can figure out your mileage tends

[MetroMPG]

Originally Posted by AaronMartinSole

How do I know if mine is a 4 or a 3 speed?

You could count the shifts as you accelerate gently from rest up to about 55 mph.

Surely 0W-20 should increase mileage, right?

Yes - minutely. But not likely enough to register above the normal variation in tank-to-tank comparisons.

That's the only "mod" you made, by the way. Everything else is just "maintenance".

[turbovr41991]

Just give it more time and compare. No sense getting worked up about a bad tank. (similarly, a good tank might also be a fluke.) If the bad gas mileage is real, then try change your driving habits to imporve it.

[orangustang]

As others have hinted, it also kind of depends on what your 'city' driving situation is like, as you've given no real details. If you were in bumper-to-bumper traffic and idling a lot of the time, your mileage is going to be much worse than, say, a city with minimal traffic where you know the lights well enough to time them, etc.

I've been able to raise my city MPG to about highway levels by just turning the engine off at red lights and accelerating judiciously. With auto, you can't EOC as effectively as I can with a manual transmission (no bump starting), but you should be able to pop it into neutral and turn the engine off when you're going to have to wait awhile in traffic or at a light.

[Vman455]

The 3-speed auto was dropped for the US market in 2001 (with the base VE, the only Corolla that had it); yours is a 4-speed. As Metro said, the only thing you've really changed from stock is moving to a lighter oil weight which won't net you much mpg gain (if it's measurable at all). The original EPA ratings for the car were 32 city/41 highway before the revision; my parents and one of my brothers have 2004 Corollas (both automatics) and regularly see 40+mpg driving normally, so I'm not surprised at a 39 mpg all-highway fill for yours. As for the drop, you already said why: city driving and extensive idling during the maintenance work. It was unavoidable, and the car will be better off having had the fluids replaced, so I wouldn't worry about it.