Higher speed equals lower mileage? Not always...

I think your data and experience tell an interesting story.

Perhaps one reason the Prius seems more "monotonic" in it's speed/fuel consumption curve is because of its unique ECVT driveline. It eliminiates the fixed ratios which are probably the root cause of the "sweet spot" in your truck.

 

I agree that all vehicles have a mechanical sweet spot where they run at there optimum efficiency. Anyone know where it is for the 2006 Prius? Not talking about P&G but cruise control. What is the most efficient speed on flat terrain?

 

<div class='quotetop'>QUOTE(Cheap! @ Jul 6 2006, 04:26 PM) [snapback]282222[/snapback]</div>

There's been a couple places where this is gathered:
http://privatenrg.com/#Bill_Moores - watts/mile from 40mph to 80mph. Also nice discussion on wind effects

Priuschat had a good thread recently (look in the fuel economy forum!), I like this chart:
http://priuschat.com/index.php?showtopic=1...id=210092&st=26
(I had to find this using the advanced features of google - set it to return results from only priuschat.com, since I haven't had much luck with the local search feature when using multiple words).

Basically there's a cutoff point above 40mph, and maximum mpg is about 33 mph.
The folks that got 109 mpg in their Prius used the pulse-and-glide technique between 40 mph and 30 mph continuously.

For other vehicles (standard transmission), my understanding the sweet spot is right after the transmission is shifted into the highest gear (often in the 40's mph) - best rpm/distance covered ratio and before excess speed causes high wind drag. Not sure why 80mph is better than 70 mph for your SUV, but I bet 55 mph would trump both.

 

<div class='quotetop'>QUOTE(nerfer @ Jul 6 2006, 06:20 PM) [snapback]282238[/snapback]</div>

Especially when you factor in getting rammed repeatedly from behind giving you that free turbo boost effect.

 

The answer is obvious. You have an automatic and it its lower revs in a higher gear. Not rocket science. Case solved.

 

<div class='quotetop'>QUOTE(glenhead @ Jul 11 2006, 11:08 AM) [snapback]284451[/snapback]</div>

Well I'm unsure of the way the ECU manages fuel in a piston engine but the rotary ECU cycles through several different fuel delivery modes. I can conly remember the name of two of them (there's about 5) one is "open loop" and the other is "double loop" anyway this system for some reason give you the best mileage at 90 Mp/h in 4th at around 4500 RPM or so, I don't understand why but it doeas. Maybe the Ford has an ECU controlled fuel delivery system that helps it out. Also maybe since the explorer is such a high vehicle, the air is causeing a slight bit of lift that lessens the load on the wheels and drivetrain but a 150 RPM difference would barely effect mileage. There a little more complex but these could possibly be close to your answer.

 

<div class='quotetop'>QUOTE(glenhead @ Jul 6 2006, 10:42 AM) [snapback]282025[/snapback]</div>

Do you have the GT4 or GT5 gear option? That is, does your vehicle have 3.73 gearing or 4.10 gearing? If I recall, the build code list is on the inside of the glovebox.

I had a 2000 GMC Sierra that I special ordered to pull a 6,000 lb camper: half ton 4x4, SLT, GT5 (4.10 gearing), Z71 offroad, towing package, etc. With the 4.10 gears, I almost ALWAYS got better fuel economy than comparable Chevy/GMC trucks with 3.73 gears, usually by 2-3 MPG at the normal highway speeds here.

In Manitoba, most of the traffic is moving at around 110 km/h or about 70 MPH. Unless I went faster than 110 - which I rarely did - I got better fuel economy. The difference was even more pronounced at speeds of 60-80 km/h.

It's my opinion the 5.3 Vortec has a sweet spot around 2200-2500 RPM. Any slower than that, you're not really "lugging" the vehicle but you're using more gas. I also carefully tracked the fuel consumption as I'm given an allowance for business mileage.

Another odd thing: Driving around Winnipeg, at speeds up to 80 km/h, I got around 1.5 MPG better by leaving the shift in 3, instead of OD.

 

You may actually be running the engine under a higher load, and thus
maybe more efficiently, against air resistance at the higher speed.
If your transmission had an additional gear, I bet you'd top 20 mpg
more often.
.
_H*

 

<div class='quotetop'>QUOTE(glenhead @ Jul 12 2006, 08:55 AM) [snapback]284911[/snapback]</div>

I'll also assume you have the Z82 "locking" rearend made by Eaton. With towing of about 600 initial miles, the shop manual recommends taking the rear cover off the differential to wipe out accumulated sludge and to clean the magnet off. My 2000 had a drain plug, if I recall the +2003 did away with the drain plug. Your axle is probably made by AAM (American Axle and Manufacturing).

Hint: it's far easier to wrestle the cover off if you first lower and remove the spare tire. That's always a good time to lube up the spare tire crank too.

After I did the initial service, the inside of the case was sludgy, there was a dark gray film on the sheet metal cover, and the magnet was loaded with particles. I became a bit concerned so did another service about 5,000km later, and the inside was spotless. It really does pay to do an early initial axle service, especially if you do it yourself.

On the issue of gearing, from what I have seen of the newer pickup trucks and SUV's, they are grossly too high for gearing. For example, the 2005 Ford Expedition a co-worker has will cruise on the Trans Canada at 110 km/h and around 1,500 rpm. When he pulls his camper, the thing will barely get out of its way.

I'd have to guess the domestics for some reason geared all their pickups and SUV's for empty 75 MPH cruising. Load them up and they barely get out of their way. The 4.10 gearing, or even lower, would actually IMPROVE fuel economy at city and interurban speeds, especialy when the vehicle is used for its intended purpose of towing or hauling.

<div class='quotetop'>QUOTE(hobbit @ Jul 12 2006, 09:43 AM) [snapback]284929[/snapback]</div>

One co-worker has a '05 Expedition, another has an early production '06 Lincoln Navigator. The Navigator is obviously more luxurious, but it also has a ZF 6 speed auto transmission instead of the Ford 4 speed Slush-o-matic.

They've compared notes and the Navigator routinely gets 1-2 MPG better, and is rated to tow more too. The co-worker with the '06 Range Rover also has a ZF 6 speed auto, and that beast always seems to know exactly what gear to be in. Very impressive for such a huge thing.