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In trying to be a complete researcher, I added my 2002 Montana VIN to the GM owners site to see what secrets it might reveal. There was a link to 10 Ways You Can Save Gas. There are 9 good things, then this:

4. Open windows at slow speeds. Use A/C on highways.
Around town, turn your air conditioning off and roll down the windows. On the highway, open windows create drag at speeds of 40 mph or more, so roll them up and use the air.

I agree with the first part, its the AC part on the highway that makes me go :confused: I heard this recommended back in the early 80's and I never got it to work. I know open windows do create drag, but rob more horsepower than the compressor?

I'm sure there are some "it depends" involved, and to be fair I guess I should try it. Something tells me I will not like it.

Here is the link:
http://www.goodwrench.com/Tips/FuelEfficiency.jsp#savegas

Hi Paul:

In most sedans, the Cd even with windows open is better than using A/C. In a Montana however, the difference between the two at 65 mph is probably pretty close.

Regarding the site, have you ever seen much from a FE standpoint that they have done over there?

Good Luck

Wayne

Thanks Wayne, I should give it a try. Right now my driving with this van is all urban, but that will change in future and more highway will be there, no sooner than winter so ac will be the last thing on mind ;).

The rest of the site is reasonably good advice and is mostly echoed here. The first two are related to even driving, keeping the speed down and cruise control. I wouldn't expect GM to evangelize P&G, so that's about the best advice otherwise. Three about how (not to) fill up, all valid. Another about reducing weight in the car. Another on don't accelerate up hill.
The last one on the roof rack is too late because they sold it to me with one on. I use it sometimes.

Thanks for the response.

Paul

Hi Paul:

We do not evangelize anything and P&G is rarely used for most. FAS’ing at lights, DWL and Smart Braking plus Anticipatory focus and 5Blinks, Alternate routes, and Rabbit Timing are all good when they can be applied as well. I did not read it but topping off to avoid yet another wasted trip to the station if that is what ht4ey were talking about.

I guess the thing that bothers me is we have seen the same from the likes of the EPA, CR, C&D and even the EPA yet ask any of the authors what they receive on a day to day basis and it will make you puke. That is the Seriously part that everyone seems to miss :(

Good Luck

Wayne

Thanks Wayne, I should give it a try. Right now my driving with this van is all urban, but that will change in future and more highway will be there, no sooner than winter so ac will be the last thing on mind ;).

The rest of the site is reasonably good advice and is mostly echoed here. The first two are related to even driving, keeping the speed down and cruise control. I wouldn't expect GM to evangelize P&G, so that's about the best advice otherwise. Three about how (not to) fill up, all valid. Another about reducing weight in the car. Another on don't accelerate up hill.
The last one on the roof rack is too late because they sold it to me with one on. I use it sometimes.

Thanks for the response.

PaulIf your roof rack has any lateral crossbars that can be removed, do.

Otherwise, load bars that run front-to-back have virtually no impact on fuel economy. Might as well leave them on (as I have done on my Jetta wagon). From what I can see Googling pictures of Montana, I think you're fine.

THanks, that's a good idea. I have moved them front to back, but possibly they come out. The fuel gage has been broken for years and I always assumed 20 gallons, and the gm site shows its actually 25. I have been carrying around 40 -50lbs of fuel I don't need to.

If your roof rack has any lateral crossbars that can be removed, do.

Otherwise, load bars that run front-to-back have virtually no impact on fuel economy. Might as well leave them on (as I have done on my Jetta wagon). From what I can see Googling pictures of Montana, I think you're fine.

Wayne, sorry didn't mean my comments to be taken that way. I meant that they recommend good basic techniques including alternate routes, but none of the other more advanced techniques discussed on cleanmpg. What I meant was that as meaningful and useful as it would be for drivers to adopt the appropriate techniques, I don't think GM will be listing them on a web site or owners manual. Yet.

The topping off tips from them were to fill up early or late in the day and not all the way up neck, some vapor space is needed in the tank. They suggest stopping when the nozzle first clicks.

Hi Paul:

We do not evangelize anything and P&G is rarely used for most. FAS’ing at lights, DWL and Smart Braking plus Anticipatory focus and 5Blinks, Alternate routes, and Rabbit Timing are all good when they can be applied as well. I did not read it but topping off to avoid yet another wasted trip to the station if that is what ht4ey were talking about.

I guess the thing that bothers me is we have seen the same from the likes of the EPA, CR, C&D and even the EPA yet ask any of the authors what they receive on a day to day basis and it will make you puke. That is the Seriously part that everyone seems to miss :(

Good Luck

Wayne

Hi Paul:

No problem and anything to help reduce consumption no matter where it comes from is truly is a good thing.

Good Luck

Wayne

I have read that the longitudinal members of a roof-rack still impact your FE, just not as much as the lateral cross-bars.

Aero effects are much greater at higher speeds, while the power required to run the AC is relatively constant. (Possibly lower at higher speeds because the consensor cools more effectively from greater air movement!) So there should be some point where the hit from having wide-open windows is greater than the hit from running the AC. I'm guessing that, in my car, that point is faster than the car can actually go... ;)

Larger engines tend not to "notice" the AC as much, while smaller less powerful engines seem to take a larger hit on FE when it is on.

Vehicles with poor aerodynamics may not see as much of an increase in aero drag as vehicles with good aero from the disruption caused by opening a window.

So there are a lot of factors, so they could very well be right about windows vs. AC given some particular set of assumptions. (Speed, engine size, how far open the windows are, etc.)

-soD

I have read that the longitudinal members of a roof-rack still impact your FE, just not as much as the lateral cross-bars.No doubt measurably so, but nothing compared to the crossbars. The crossbars on a typical roof rack easily have 10x the frontal area of the side bars.

Just a small plug for Prorac http://www.prorac.com/

They are an aftermarket rack that goes on relatively easily; Carefully lay out, and then drill like 4 or 5 holes per rail, zap in some big sheet metal screws & sealant and you're done.

But for my $, the big deal is the very low profile when the crossbars are off.
Any hypermilers who need to add a rack should check these out.

Very nice, TheFridge. That's a lot easier on-and-off than the Yakima solutions. When I eventually replace the Jetta with a Prius I'll take a serious look at those.