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Another tip is to roll down your windows when driving in town versus using the ac, but when you go higher speeds, put your windows up and use the ac. I've noticed a big difference in mileage by doing this.

To really beat the system, you can turn on the vent for the outside air but leave the AC off and windows up. This means you have no compressor drag or air drag from the windows being down.

*B2* wrote:

Another tip is to roll down your windows when driving in town versus using the ac, but when you go higher speeds, put your windows up and use the ac. I've noticed a big difference in mileage by doing this.

To really beat the system, you can turn on the vent for the outside air but leave the AC off and windows up. This means you have no compressor drag or air drag from the windows being down.

There is only so much "savings" I can do and keep sane at the same time. During the dog days of summer I'm using the A/C ALL the time. On a day like today (sunny, temps in the low 70's and very low humidity), I'm letting the wind blow thru my hair.....what's left of it!

Personally my SE can get 30mpg on highway miles and 22ish on all my back road driving. I get an average of 25mpg very consistently. I have found myself doing everything to save fuel mileage, but for my sanity I just drive and try to take it easy most of the time. I was consistently monitoring every movement in my gas gauge and realized that I was obsessed.

But like you said 10%-15% of the time, there's gotta be that adrenaline rush that reminds you what driving a 3800 is all about, even if it's not boosted.

Personally, I just drive the *dang* thing easy, and sometimes I really get on it.

What kind of mpg's are you getting now and what kind of driving are you doing?

Just Checked the Mileage today... With the Ported Lower Intake, Intense Intake kit, Magnaflow Kitty Cat... I am doing 25 Mpg Mixed On the 95 Bonneville

I get 21-23 so far on the SSEi, depending on how hard i beat on it, last tank never got above 20. -my dad, who pays for 75% of my gas, LOL :sad5:

Hrmm... You guys are doing a bit better than me on MPG's. Sounds like I have some work to do.

*B2* wrote:

Another tip is to roll down your windows when driving in town versus using the ac, but when you go higher speeds, put your windows up and use the ac. I've noticed a big difference in mileage by doing this.

To really beat the system, you can turn on the vent for the outside air but leave the AC off and windows up. This means you have no compressor drag or air drag from the windows being down.

That is not a bad idea for people that don't live in the south. Our average temp in the summer is over 100 we need AC. I try not to use AC if it is under 95 outside.

b18jason wrote:Another tip is to roll down your windows when driving in town versus using the ac, but when you go higher speeds, put your windows up and use the ac. I've noticed a big difference in mileage by doing this.

they proved this on MythBusters, going under about 45 MPH, you're better with windows down.

nicklikesmilk wrote:

b18jason wrote:Another tip is to roll down your windows when driving in town versus using the ac, but when you go higher speeds, put your windows up and use the ac. I've noticed a big difference in mileage by doing this.

they proved this on MythBusters, going under about 45 MPH, you're better with windows down.

I love that show - I saw that episode. I use vents or A/C on interstate/highways.

I used to drive with my tailgate down on my old Isuzu pickup - little did I know I was actually hurting my MPG's....

I'm getting 24.4 right now in my 00 SSEi, which I think is respectable. I put the cruise on 70 on my way to the office in the mornings, and I do get on it occasionally Amazingly, the DIC was accurate with my calculations on last fill up .. 442 miles and pumped 18.1 gallons (yes I let it get way too low I know) I think I may beat that mileage this go round. I still have over 1/4 tank and have been almost 380 miles and its been 2 1/2 weeks since that last fill up. Thats with boltons (PCM, FWI, Hogan 3" DP and High Flow Cat, Delco Wires, 41-985's (One colder heat range) 3.4" , aluminum LIM Gaskets, new 02's, 180*, etc) so we will see.. I'm pleased right now.

clm2112 wrote:
Another gross change that increase mpg is to lower the final drive ratio in the transmission. If you have the torque available, you can run a numerically lower final gear..so the engine is turning slower in top gear while cruising. Knock off a hundred rpm from the cruise, you might pick up an extra mpg in fuel consumption.

Always wondered about this.

The trade off to really tall gearing (trust me, i know) is LOTS of throttle getting off the line and up to city speeds. While I realize that I am probably getting a little more mileage on the highway, I think something shorter than the 2.73's would actually improve city mileage. Maybe something like a 3.06 would be the sweet spot with a L36?

I can do about 17.5 average for city and 23 highway with the truck if I REALLY try, assuming 65 on the highway. Average about 14.5 city, 18 highway with normal driving, exactly what the EPA rated it. Average at about 15.5

To really get the good numbers, I take corners faster, change lanes to go around turning cars, and other obstacles to maintain the most efficient flow, coast up to a light if its red, very lightly apply the gas, using only low end power, and keeping the A/C off, and windows down when I'm in the city. 17.5 average in the city is PRETTY *dang* GOOD considering thats about what I get in the bonneville.

Now to really push the numbers in the bonneville, I do the same thing...works perfectly. I average about 19 city, 28 highway with normal driving, average about 22.5-23. If i REALLY try to be nice, I can get 25 city, 34 highway, assuming 65 on the highway.

Bonneville needs a full tune up though...imagine it'll get better mileage once i get into it when i get it down here.

Last fall i went to Georgia in the bonnie and noticed if i drove over 70 i was getting 25 mpg and under 70 was over 30 mpg.

My grandpa drove an SE back from colorado, because my aunt in CO sold it to my aunt on Hastings, MN, and he got 25, and he had it checked over by the local mechanic, and he said he would've gotten over 30 if he had had the tires fully inflated. We have way too many b-villes in our family. Aunt has an SE, dad has an SLE through work, and i have my SSEi, all 2000+'s. LOL

Bigerik wrote:The trade off to really tall gearing (trust me, i know) is LOTS of throttle getting off the line and up to city speeds. While I realize that I am probably getting a little more mileage on the highway, I think something shorter than the 2.73's would actually improve city mileage. Maybe something like a 3.06 would be the sweet spot with a L36?

It will be different for everybody. We all drive differently and in different terrain.

Florida is flat-land with 70mph speed limits. numerically low gear ratio helps if the car spends most of it's life on the interstates and just manages to get up to speed in top gear with the TCC locked up.

In a different enviroment, the optimal gear ratio and speed that puts you in top gear with the TCC locked up is the right one.

Ok, here's a practical example of gear ratios in action. I did a little impromptu test on the '90 Bonnie on the way home. Instead of trying to figure what gear ratio gave the most efficient cruise, I simply inverted the problem to figure out what cruising speed gave me the lowest engine rpm. In the three examples, the car is cruising at a steady speed with the throttle at a constant position.

45mph, 3rd gear, TCC locked, 2100 rpm

53mph, transmission just shifted and held 4th gear with TCC locked, 1600 rpm.

60mph, 4th gear TCC locked, 2100 rpm

See what I mean.. at 53 mph the car is doing it's most efficient fuel burn vs vehicle speed. (The number isn't really all that surprising, this car was built at a time when the national speed limit was 55mph to conserve energy)

Nice info there clm. Makes me want to try that out with mine tonight and see what I get. I wonder what speeds I will get...

b18jason wrote:Last fall i went to Georgia in the bonnie and noticed if i drove over 70 i was getting 25 mpg and under 70 was over 30 mpg.

Sounds just like my experiences in the '93. It did not like getting above 75MPH at all, prob passing the torque peak IIRC.

nicklikesmilk wrote:

b18jason wrote:Another tip is to roll down your windows when driving in town versus using the ac, but when you go higher speeds, put your windows up and use the ac. I've noticed a big difference in mileage by doing this.

they proved this on MythBusters, going under about 45 MPH, you're better with windows down.

Sounds like an ok place to start, but it'll be very car dependant. 2 door 4 door, sunroof, no sunroof, hatch, even how the leading and trailing edges of the A pillar are shaped, etc.

Keep in mind having the window open 1/3 of the way still gets fresh air in, without the huge drag of the entire window down.

clm2112 wrote:

Bigerik wrote:The trade off to really tall gearing (trust me, i know) is LOTS of throttle getting off the line and up to city speeds. While I realize that I am probably getting a little more mileage on the highway, I think something shorter than the 2.73's would actually improve city mileage. Maybe something like a 3.06 would be the sweet spot with a L36?

It will be different for everybody. We all drive differently and in different terrain.

Florida is flat-land with 70mph speed limits. numerically low gear ratio helps if the car spends most of it's life on the interstates and just manages to get up to speed in top gear with the TCC locked up.

In a different enviroment, the optimal gear ratio and speed that puts you in top gear with the TCC locked up is the right one.

Don't disagree with any of that. My point was however, that those uber tall gears that work so well on long highway drives actually hurt mileage around town. Driving for max economy using those gears I would probably end up with a tractor trailer driving over me.
Interestingly, the EPA mileage results showed no difference between the tall ones and the 3.06's in the Olds. Probably same for the Bonnevilles, but I don't have those numbers in front of me.

2000 Pontiac Bonneville courtesy of www.cars.com/reseach

City - 18-19

Highway - 27-30

I would imagine those #'s are an average of L36 vs. L67 with all 3 gear ratios accounted for.