My 0.02-
This first part isn’t aligned exactly with the OP questions... Also might appear to contradict responses I made to similar questions in the past, but after some more thinking... Although the question is completely sincere, “At what RPM should I shift up / down?” is too simplistic, and defies a concrete answer. Other things must be factored in, such as: (ignoring weather & safety conditions...)
- Is gravity presently also helping to accelerate or trying to decelerate the car ? (downhill / uphill)
- Is the car lightly loaded or heavily loaded?
- Is slow acceleration acceptable, or is near-max performance needed?
- Further, during the time when the engine has not yet reached its full operating temperature, many people believe it is beneficial to limit the max operating RPM to some extent, and also to limit the amount of torque requested from the engine well below the max it could produce.
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Those factors can combine (sometimes in different ways !) to change the answer to the shift point question. At times, I have accelerated my car in 4th gear, pulling from 1200 RPM. But those times would have been going downhill, and where gentle acceleration was acceptable, and I did not have to lug the engine (ie. operate at low RPM with heavily pushed accelerator pedal and high boost etc.)
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In general, it is recommended to keep the engine RPM above about 1900 when significant torque is being requested. Given the gear spacing of the existing manual trans, then for most driving the engine ends up operating between 2000 and 3000 RPM. But if going up a steep hill, and / or if heavily loaded, and / or if faster acceleration is desired, then it’s probably a good idea to raise the operating speed and keep the engine in the 2500-3500 range, maybe higher. Note I’m not talking about drag racing here- for the absolute maximum performance, we’d get into mapping the horsepower curve and choosing the shift points such that they keep the engine in the range where integrated horsepower under the curve is maximum. That could result in different shift points for different gears. And someone else may chime in and say that it’s not max power, but max torque to govern the shifts (which would be wrong), but I digress...
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Again in general, it is desirable to let the engine spin at least 1900 RPM if it’s being asked for any significant amount of torque. Quite often the engine will be quite “happy” to maintain steady speed, on level ground, when running significantly slower than 1900. The car I commonly drive is 5spd, not 6spd, but I will offer here- I typically go through village 30MPH zones in 3rd gear at around 2000 RPM (just above 30MPH). The engine will happily carry the car in 4th gear at 33MPH at around 1600, but the problem I have there is- the torque of the diesel is so plentiful, it’s easy to creep the car up over 40MPH in 4th, thus eligible for speeding tickets. So I just let it sing along in 3rd, and if the RPMs get too high, it’s a reminder for me to back off a bit.
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Probably rude to close this without touching on the OP questions!...
I agree with above responses, there’s nothing specifically detrimental about coasting in neutral. Due to the computer control, the feature is built in such that the fuel supply is shut off if engine speed above idle is detected along with accelerator not depressed. So in that condition, zero fuel is consumed. But the OP counterpoint is valid; in that case, the car is slowing down faster due to the engine braking effect, so what is actually cheaper- to coast farther and easier in neutral, but the engine is consuming fuel, or to coast with engine braking, but consuming no fuel? I can’t answer that, only to quote another forum regular (whose name I can’t recall): Drive more, worry less. I also agree there is no detriment to the manual trans for coasting in gear. Personally I am among the group that typically does not coast in neutral, generally always keeps the engine coupled to the drivetrain while the car is moving. It’s what I was taught, and I observe vast majority of skilled performance drivers do same thing- rarely coast in neutral. I’m sure we’ll find a counter-point somewhere...
I will insert one other thing, though- I believe it's good to be in the habit of NOT sitting with the clutch pedal depressed for long periods of time. I will generally idle at a stop light in neutral with foot OFF the clutch. Watch the opposing light for when it turns yellow, and use the clutch to engage first gear only a few seconds before getting under way. That saves wear on the throwout bearing and pressure plate (not to mention your clutch foot).
Enjoy your TDI !!