Another mileage thread

[Ross]

Back during the winter I was getting about 20 MPG in mostly city driving and about 22 MPG in mostly highway driving. I'm now lucky to get 20 on the highway, and I just finished a tank at about 16 MPG mostly city. Driving pretty conservatively, flat southeast Texas roads.
Two possibilities:
1. Hotter weather equals less dense air, so poorer performance, including mileage. Been really hot down here.
2. During the winter, I wasn't driving with the AC on all the time, like I am now. AC use reduces both power and mileage.

Comments? A lot of you know a lot more about this than I do.

[2003 MIB]

22 mpg (mostly highway) but same nasty hot temps with AC on. I don't count on that when the 4.10 is installed. I drive pretty conservatively as a rule. O/D off around town but rarely over 80 on the freeway.

[Hemlock]

WITH 4.10S ,17 TOWN, 21HWY. NOT LATE OFTEN .

[Jeff]

20 Hwy/ 17 Leadfootin'

[jgc61sr2002]

Averaged 24 MPG on a recent trip to Collinsville, IL. Kept tack at 2200 RMP about 75 MPH.

[Zack]

I beat on my car so bad Im lucky to ever see 15mpg. Seriously.

[amerikan]

i am very disappointed after stage 1 mods concerning MPG. 11 mpg city.. maybe 3 times WOT. highway i dont know.

[LincMercLover]

Damn kids and their race cars blairing that rock n roll music... :shake:

[MMManic]

All stock- 19 mpg around town w/heavy foot
Highway= ? Haven't made any trips yet.

[rct]

12 - 15 around town, depending on who ELSE is around. Heh. Highway, I don't have much on that yet. Driving across America and back August-September, so I'll know better then.

I don't really care though. Gas wasn't even a thought when I bought it, and I wouldn'ta bought it if gas was a thought.

[SergntMac]

Last road trip from Chicago to Indy;

From Chicago on Chicago 93 octane gas = 19.7 MPG

From Indy on Indy 94 octane gas = 21.8

Go figure...

[Mikeenh]

I averaged 18.4 mpg on my trip from York, PA to NH. 550 miles @ 65 to 80 mph towing this trailer that weighs 1,900 pounds. I put in 2 small bottles of Chevron Techron injector cleaner on the trip down.

[Ross]

Does anyone have any information about my questions?
1. Is the hot air causing lower mileage than cold air?
2. Is using the AC constantly causing significant reduction in mileage?

Thanks

[Dr Caleb]

I would say, Yes. A/C is know to affect economy. Heat reduced HP. Heat also increases tire pressure, and can affect milage.
I don't know if these would add up to the ~3 or 4 mpg you're seeing, but I wouldn't be surprised.

[TripleTransAm]

I've seen the opposite occur (winter driving resulting in lower mileage) but with increased A/C use, yes it will consume a bit more. That much more? Sounds fishy. Also, some gas companies reformulate their fuels for winter use, but again that usually contributes to the opposite: increased consumption during the winter. The reasoning for the cold weather consumption: more oxygen per quantity of air at colder temperatures, requiring a richer mixture.

Now here's something to consider:
I just recently swapped out all 8 spark plugs on my WS6, went with NGK coppers instead of the AC Delco platinums, regapped to my own specs...
Followed by a fuel filter change, then went to get my alignment checked: the toe was slightly off, although caster and camber were still pretty close to what I spec'ed close to 3 years ago. So I just got the toe corrected back to my preferred '0.00' .

My point: my first tankful produced an improvement of about 25% mileage-wise, and what seems to be a much improved low end response (probably more a function of my custom gapping than the alignment). But the 25% increase?

So maybe it's worthwhile after all to get one's alignment checked out now and again, perhaps more important on heavier vehicles with stickier tires. Perhaps a misalignment in toe specs can bring on a large impact in mileage.

And while we're talking spark plugs... might be a good idea to check for fouling. In hotter climates, the dreaded 'pcm-reflash' issue might not be as noticeable (just a wild guess here) but the long-term fouling might sneak up on you anyway.

[Ross]

TTA, what gap did you use? How did you get your own gap that you referenced?

[Dr Caleb]

When using the "Defrost" option in the winter, it does engage the A/C. I don't know about you, but I do warm up my car which contributes to poorer milage too.

Speaking of the fuel filter, perhaps he's gotten bad fuel, clogging the filter.

[TripleTransAm]

Originally posted by Ross
TTA, what gap did you use? How did you get your own gap that you referenced?

I used a gapping tool. I've got two, actually... one is the cheap kind with little loops around a circular flat disc, each loop is a preset thickness (0.060, 0.045, 0.050, etc.) and the other is the type that looks like a Swiss Army knife, except it's loaded with flat strips of varying thickness... with a little bending, you can get pretty much any gap simply by combining different thicknesses. The circular disc tool even has a little 'hook' that helps bend the outer electrode without risk of mangling its arc.

I haven't checked my MM's plugs yet (about 7500 miles on it) but on the WS6 I initially gapped my original AC Delcos at 0.055 instead of the recommended 0.060, and went on to pull my 13.4 @ 107 best time. That was in 2000. I haven't checked what gap those plugs were at when I removed them last week (39000 miles) but the platinum pucks on every outer electrode were mostly all eaten away. Whenever I get a chance, I'll check the old ones, but I'm thinking they must have been at 0.065 or more!

Replaced them with NGK coppers... TR5 model, and I gapped them at 0.050 this time. The car pulls strong and mileage is up, as mentioned. I'll check them in about 10000 miles to verify if there is any fouling, with my mostly-docile way of driving, but power-wise: I did liquify the tires with little effort during the post-change "road test" so I guess it likes those plugs for now.

I've checked the MM's recommended gap in the service manual (it's actually a RANGE of gaps, oddly enough). Once I check the plugs, I'll make sure they're gapped on the tight end of the range, and all even with each other.

[drobin]

Ross, try experimenting with different brands of fuel. My MM prefers Exxon and I always use premium. Getting 20/21 highway and 16/17 city. My right foot normally causes poor fuel economy, so I try not to worry about this and long as she's running strong, sound good and smooth, I'm happy.


Donald

[cruzer]

We are not allowed to put drained avgas back in our planes---anyone have any idea how 100 octane low lead avgas would do in this engine--I have a few gallons fresh out of the tank ???

[Ross]

Cruzer, you just gave me an idea for my next mod! Aviation fuel and a set of wings!


Remember the old song "Little Duece Coupe"?

When someone comes up to me he don't even try,
'Cause if it had a set of wings, man,
You know she could fly,
She's my little duece coupe,
You don't know what I got.