20 MPG in Chevy Tahoe, Why?
 

Traveling 400 miles in Texas with one thing in mind. Economy. I was driving the family car, a '02 Tahoe (14/17mpg with a Vortec V-8) and gained a mere 3 mpg. I kept the speed low, sped up on downhills, coasted up hills, and pulsed to an extent. I kept the A/C off (to the great chagrin of my mother) and all vehicle conditions were ideal, although stock.

In 98 deg. Texas weather, is it advisable to block the grille? I understand AC won't work well, but hey, $4.00/gal? Crazy becomes wise at that point.

What did I do wrong? Why only 3 extra MPG? Should I have P&G'd more? With the auto tranny in the Tahoe, it decelerated rapidly with no gas, and popping it into N every 8 seconds for 6 hours seems a very bad idea. Advice?

Thank you for the 3 mpg, but I want more!

Logan W.

3 MPG is a big difference on a low MPG vehicle. You saved around 15$ on that trip by my calculations.

That's still almost a 20% improvement.

One of the problems with something like the Tahoe is aerodynamics and weight. To overcome rolling resistance and aero at 70-75mph, you probably need 40-50hp just to cruise!

Best thing on a heavier and less aerodynamic vehicle is to keep speeds low...

As an example, 85mph in my Aristo (similar to GS300) is just about the same horsepower as 65mph in my wifes Mazda Tribute. Vehicles weigh similar, but aerodynamics are vastly different.

Check out the bottom graph I made up in this thread. I'd lower results a little for the extra size of the Tahoe perhaps, but may give you an idea of where to be.

http://ecomodder.com/forum/showthrea...html#post41430

My question is was the $15 worth the aggravation? I use hypermiling techniques when alone but I'd never submit my family to 6 hours in 98 degree Texas heat without A/C. If that money was the difference between going or not going then the shared sacrifice is understandable. If that had been my mom she would have said: "Here's a $20, put on the F&*%#g A/C!

For me I'd say on a trip no its not worth it, but daily driven it does add up

you have to look at the % improvement, not just the numbers. 3 mpg is a lot for 14/17..

On a road trip, in a large vehicle with a huge Cd, your best bet is to inflate the tires somewhere between factory spec and sidewall max, use the a/c on recirculate, and drive at the speed limit, tailing a truck by 5+ car lengths for safety.

P&G is not advisable for an automatic transmission, plus you have to use the starter to restart the engine, which uses lots of electrical energy that must be made up by the alternator. In a manual, you can bump start and eliminate damage and electrical losses

The ac was broke
 

Therefore, we could only use it below 70mph and only on low uphill grades. Compressor is going out.

I think there was another thread complaining that MPG is a poor measure because 3mpg gain at 17 is twice as big as a 3mpg gain at 34. But just think, that means your next 3 should be cake :)

Not only is the Tahoe about as sleek as a box of Wheaties, but that automatic and that half-ton of four wheel drive machinery you tote around not doing you any favors.

But people didn't lay out the big bucks for SUVs without a reason. They do a lot of things well. Because there are so many of these monsters and because people (especially women) like them, if one can get a 25% improvement that is a huge improvement in national gasoline consumption.

I think with the right mods (which would also open new vistas of hypermiling), you could squeeze 23-25 MPG out of it, and retain most of the functionality.

I get 27 MPG out of a bigger vehicle and run the AC anytime I get hot - for a porker like me thats April through mid-October here on the scorched steppes of central Indiana.

Here's a couple of thoughts.

Do you use the four-wheel drive? Most SUVs really do not use it.

If yes forget about it.

If no, try this. Remove the half-shafts on the front axle. This way the front axles lose all the drag of the front pumpkin and transfer case. Even with the hubs unlocked there is some friction from all that machinery. This is fairly easy to reverse in the late fall when you may really need 4x4.

Also, check your disc brakes for rubbing. The metallic brakes used these days tend to rust. Most of the pucks are cleaned off by brake action but the edges are not swept by the discs so they can rust, which makes them swell up and rub at the edges.

3 mpg will save you more $$$ than 7 mpg in my car! Do the math! That's about 25% savings!

I'd say before you do this, check to make sure your unit bearings are designed to run without the half shafts. For a Jeep, the bears will fall apart without the shafts installed, or bare minimum the stub shafts.

If you don't need the 4x4 and have to have the half-shafts to keep your wheel bearings together, the surgery gets more serious. Pull the diff and ring gear. That will lose all the friction from the front drive. At that point you may as well remove the transfer case and lengthen the rear drive shaft.

Most folks are not that radical about MPG - yet.

If that thingis automatic you are kind of limited. Like they have said 3mpg is pretty good for a vehicle rated in the mid 10's. YOu have to realize there are mechnical limits to what your vehicle can do mpg wise. You have a heavy non aerodynamic vehicle, this is probably your biggest hurdle. MAybe try some extensive weight reduction? Then you have a very hungry powertrain. I mean the parasitic loss of a v8 chevy ohv with all the 4wd junk and an automatic tranny is phenomenal. Like the others said see if you can get rid of the frontportion of you 4wd. drive at a sustained low speed, like 60-65 on the highway(your big, people won't mind lol) i wouldn't recomend speeding up and coasting and speeding up again in something that big and heavy. It takes alot of gas to speed back up to those speeds. For instance my friend gets 24mpg cruising in his cherokee, but under acceleration he gets about 6mpg. So cruising is more efficient for him unless he has a considerable hill. My civic which weighs like 1200 pounds less with amore efficient engine requires less gas to speed back upso it can work in the right situations.

In the end you may think about getting something like a honda odyssey that's rated for i believe 30mpg highway. But i think with the right driving, some weight reduction, 4wd disconnect, driving slow and sustained speed, and whatever else you can think of, i think you could see 24mpg highway, but thats probably the max unless you do some more extensive mods.
But definatly don't give up. Higher mpg's are always better.

A crazy alternative would be to find someone with a 2WD Tahoe that wants to covert to 4WD then just swap stuff out.

Sounds like a good idea to me:thumbup:

get a scangauge.
remove your cross bars on the roof rack(most tahoes ahve them)
with the scangauge, check your temp. if it is like my friends silverado runs about 200 deg, and never goes above 203ish.
then do a grill block start from the top and work your way down.
if your a/c compressor is going bad either fix it or ditch it....it causes drag.
iflate your tires.

re:
 

May I suggest drafting big trucks!!!! Obviously, be safe about it, and I don't want a nasty email when a rock cracks your windshield, BUT......

I have been doing this for the last few days and have seen big improvements. I use the digital mpg display to determine the difference -- I don't have a scanguage -- and there appears to be a 3-4 mpg increase (24 to 28 or so) when I cruise behind a big truck at 55mph, as opposed to having no one in front of me. This is based on limited experience (so far), but there is a very noticeable difference, at the very least. More info to follow, once I collect some more data.

FYI: I have an '07 Tundra, which is about as aerodynamic as, well, something that's not aerodynamic at all. I think the drafting technique helps us boxy truck guys far more than it helps the little 40+ mpg folk.

Good luck with the Tahoe.

I agree! but I still draft. Not all close, but I ride behind trucks when they pop up...