Quote:
Originally Posted by MetroMPG
So the concensus seems to be: it's OK to cruise at low RPM and low load.
If you need more power, you should downshift if:
1) the engine lugs (shudders) when you push the accelerator further, or
2) you cause the engine to go into open loop (typically at very high loads - ie. pedal near the floor), which can be monitored with a ScanGauge
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Those vibrations can get really bad really quickly if you're loading up the engine like that, so I'd have to agree. Plus, when you're making the engine vibrate wildly, you're wasting fuel... that vibration energy has to come from somewhere, eh?
I can put my truck into 5th gear at 20 MPH and still get up to speed, but it takes forever and a very light right foot. I rather do a 2/4/5, and I've only had it for a week, and driven it just over 100 miles, so beyond "first impressions", I'm not an authority on how to drive my truck, by any means. I'm still waiting to get it fixed up and put the MPGuino in, so I can have some real-time feedback and try a few different things.
I also think that the tenet we endorse which has people accelerating at high load/low RPM needs to be further explained because of this. It should rather state that accelerating at the highest load you can use without creating excess vibrations or shuddering/detonation at the lowest RPM for your speed (highest gear) may be the most efficient. This introduces a new idea, that maybe the absolute highest gear you can use isn't necessarily best for your situation, and you should adjust accordingly, because even though you're at a higher RPM/lower load in a lower range, you may be closer to "optimum" for the shorter time you're accelerating.
I know it seems like common sense, but that's not nearly as "common" as the name would imply, and people do follow suggestions to the letter, as though they were directives.