Sorry guys, I disagree. On a mild downgrade in my automatic Tacoma, once it has locked the torque converter (which it does quickly) in fifth at say 40 MPH, if I lift of the gas completely the truck slows immediately. If I pop it into neutral (as I would with a manual) it rolls and maintains speed. There is mild engine braking with the auto any time you lift the gas, just as there would be with the manual. But with the manual it's harmless to go in and out of neutral. I'm less sure that's benign for an automatic. Any transmission techs out there with an opinion about whether it's harmful to go in and out of neutral with an automatic?
I've had a chance to test this issue extensively with two matched Honda Civics, one manual, one automatic. The Civic automatic also does a good job of locking the torque converter under light loads -- usually a good thing. But it does kill the coasting. We got 32 mpg consistently with the manual, and are getting 28 in the same conditions with the automatic. Pretty disappointing. I would expect similar results with the Tacoma.
Per the comment earlier that the fuel injection system closes off all fuel flow when the throttle is closed, I don't know whether that's correct or not. Seems unlikely it would go below idle flows. IN any case, my point was the engine braking effect, which is more significant since you have to then apply throttle to regain speed you lose from engine braking.
The other thing that kills fuel economy with automatics is the compensated idle: fuel flow at idle is boosted slightly to compensate for the load from the torque converter. So manuals burn a bit less sitting at a stop light. All this little stuff adds up.
Again, my experience with this stuff may be unique to the city I drive in, where there's lots of free transportation to be had on the way back down the hill...
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Ahh, then you're not talking about the engine braking in that it downshifts. You're referring to Toyota's vehicles versus other manufacturers. For instance, I've driven other vehicles where when you let off the gas on a downhill, the vehicle feels like it rolls completely free and begins to pick up speed. Toyota's don't do that. All the Toyota's we've owned will provide some resistance when letting off the gas (I prefer it this way because I don't have to ride the brakes on every single downhill...freeways included). So we were talking apples and oranges from your latest description.
As far as this goes, I guess it's a personal preference. While you may not like it, I certainly do. It may also depend on the terrain you live/drive in as to whether it's beneficial or not.
As far as the fuel flow being cut off, that was an accurate statement. It has been confirmed by numerous people that have hooked up their SCAN II gauges and monitor the fuel flow while driving.
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The other thing that kills fuel economy with automatics is the compensated idle: fuel flow at idle is boosted slightly to compensate for the load from the torque converter. So manuals burn a bit less sitting at a stop light. All this little stuff adds up.
Point taken, and to address that issue, simply place the auto trans in neutral at each stop.
In my mind, though, if I had wanted to be a hyper-miler and sweat every tenth of a mpg, I would not have bought a Tacoma.
Well the Tacoma will also encounter more rolling resistance, mechanical drag, and aero resistance than a FWD car. You know, there's more components causing drag on the drivetrain in a RWD vehicle. You have this rather heavy driveshaft trying to maintain motion, the pinion gear and ring gear inside the rear end, and the solid rear axle. They're all much larger in size than their transaxle counterparts. You also have these HUGE (relative to the comparative Civic) tires moving with a tremendous amount of weight on them (also relative). The A750 is programmed to provide more engine braking to facilitate stopping such a heavy vehicle. But on any downhill grade, even with the throttle pedal down, the ECU reduces the amount of fuel injected per cycle. Lift off the pedal and injection ceases and engine braking engages.
The RA60 manual transmission is a close-ratio box (made more for the X-Runner than other models), so you won't see the kind of MPG ratings or realizations of an automatic. However, having driven an automatic 4x4 Taco for a few years now, I'd say even though the gearing is longer, the engine needs more throttle loading (= more fuel) to accelerate in top gear (which it tries to be in AT ALL times), even on flat roads versus a manual.
Once you pass the 20% throttle limit on torque converter lockup, the torque converter will unlock, bumping RPM up 500rpm and causing more parasitic drag on the drivetrain again until it locks. The transmission essentially needs to downshift into 4th gear in order to stay efficient on relatively mild hills and during mild acceleration, but the transmission programming will not allow it. Instead, it unlocks the torque converter first, if that's not enough it will eventually downshift, but by that time the need has past.
The newer model years have received some torque converter lockup tweaks in the programming, so I'm not sure how much it differs now. My experience is with a March 05 model equipped with a replacement transmission and ECU (direct replacements).
Climber76, now a few years later now and in comparing to all the guys w/ autos around here, I seem to beat their mpg (except interstate speeds). Of course probably has to do w/ the driver and the enviroment. Not much stop and go but lots of big hills & winding roads. Can always overgear when engine breaking not needed. I avg 20-20.5 mpg all summer on my 25 mi r/t commute. As other pointed out, you dont save gas by putting in N and rolling to stops anymore. But I can roll to stops just staying in whatever gear w/ foot off gas and shes not burning anything.
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Re: tacoma DC 4x4 auto vs. manual
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