2.7L Experimental Test to record impact of gear, speed on Fuel efficiency

I conducted a test on my 2.7L Tacoma today to see how speed and gear choice effects the fuel efficiency. Conclusions toward the end.

I used a scangauge 2 as my metering device. I had a straight road with a ~1% grade, 1 mile long. I would go 1400 ft from my start point, accelerate up to test speed, and set the cruise control while in the test gear (S mode). Once I reached the start point, I reset the current trip MPG on the scangauge and drove for 1 mile, and at the finish point I memorized the readout as I passed it and recorded it at my turnaround point 1400 ft beyond the finish line. I would stop to record the reading, verify my next test, then turn around and proceed to start the next test.

Temperature remained between 58 and 59 degrees for the entire test. Elevation ~6300 ft. Slight headwind uphill and tailwind downhill. This was not an absolute fuel efficiency test, this was to compare different speeds and different gears, so I'm only concerned about changes in fuel efficiency.

Some tests I did a trial 2, but I was feeling pretty confident about the ones I didn't. Even some of the ones I thought really needed a 2nd try didn't turn out that different. I didn't get as much data as I would have liked, but I needed to terminate the test for a variety of reasons. I don't think I will do this again, at least not unless someone wants to lend me their 3.5 (not remotely holding my breath on that either).

Raw Data:



Graphed results:


Conclusions:

1. When under a low load (such as going downhill) it is most efficient to use the highest gear possible. No surprises there. Running 5th as opposed to 6th when 6th is appropriate increases fuel consumption by about 10-15%. Running 4th when 5th is appropriate seems to increase fuel consumption by 20-25%.

2. When under a high load (such as hill climbing) it doesn't make a difference whether you try to run the highest gear and cause the transmission to hunt or just use the highest gear that doesn't cause hunting. The act of constantly locking and unlocking the torque converter wastes energy that takes away all the benefit of briefly being in a higher gear. Therefore, if you catch the automatic transmission hunting, it's best to shift to S mode and set the highest gear that doesn't cause hunting. Shift to S6 and every time it downshifts, downshift a gear on S mode to stop it trying to go back to that higher gear. Only return access to a higher gear when you can visually tell that the slope of the road has changed to favor a higher gear. If you can stay in that higher gear for at least 10 seconds, it's worth it, otherwise leave it in a lower gear.

3. Leaving the torque converter unlocked while producing a moderate or high amount of power is not great for efficiency. It makes no difference for low loads. If the torque converter unlocks but the truck doesn't shift going up a long hill, go ahead and downshift and get the truck to lock the converter in a lower gear. That seems to reduce fuel consumption by at least 10%.

4. Speed has a huge impact on efficiency. For a 1% grade downhill, it looks like the most efficient cruising speed was only 39 MPH in 5th. Going up a 1% grade I got the best efficiency at 36 mph in either 4th or 5th gear, but it looks like the most efficient speed may have been even slower, but I didn't gather any data for slower speeds. On level ground the most efficient speed is 39 MPH or less. Going any faster than that will have a roughly proportional toll on fuel efficiency. Going from 39 to 50 MPH increased consumption by 22% and going from 50 to 60 MPH increased consumption by 28%. It's likely that every additional 5 MPH over 40 MPH will increase consumption by at least 10%. Going downhill does slightly increase peak efficiency speed.

5. ECT power mode works by raising the shift points and keeping the engine in a higher zone of the rev range. This is very likely to have a sharp negative impact on fuel efficiency when ECT power mode is not needed (no or very light vehicle loading, downhill, tailwind, etc), but when the engine must work hard anyway, it is very likely to make no significant difference.

 

Interest tests and results. As far as going downhill with ECT on I’ve read some links saying it won’t shift to 6th and other links say it does. I tend to believe the guys who’ve observed with ECT on and being in 6th but want to test it myself.

 

You would need to be going 80 MPH before it shifts to 6th with ECT turned on.

 

You tried that? Or have a link to ECT rpm shift points?

 

On a recent 35 mile trip carrying a fairly loaded truck, I got a computer generated trip mileage of 31.6....but I stayed in fifth gear and my speed was just over 50 mph.

 

I was wrong, it actually seems to allow shifting into 6th as early as 73 MPH with ECT turned on. Video with shift points linked below.

https://youtu.be/ZfMcOJ_DBGc?t=118