Pulling the fuel flow to the engine is the WORST thing you can do to the motor, it will run near its maximum temp for a minute or two and then shut down...losing all heat rapidly. This alone is major concern for the engine to make TBO, but alas it can do great damage to the ignition system as well as spark plugs over temp can and often do change their gaps. now you have a cold engine that doesnt want to run, due to plugs not doing their jobs.
While shutting off fuel does have the potential to cause damgae to fuel-lubricated wetted components, it does not do any of the things you described.
Shutting off the fuel will not change the mixture setting; it will not therefore change the temperature while the engine is producing power. Only when the fuel runs out will the temperature change; it will then drop. Once shut down, you are correct, temperature then decreases.
Spark plugs do not overtemp when shutting of an engine using the fuel control (mixture or fuel selector, in this case).
Spark plugs do not vary their gap according to temperature, except in cases when excessive electrode errosion has taken place. Electrode errosion takes place based on the firing of the plug itself, not the burning that takes place in the cylinder.
Excessive temperatures in a cylinder lead to burned valves and occasionally a melted piston...but the primary problem with running at critical temperature settings isn't the temperature, it's the potential for detonation...which does the real damage. During a fuel shutoff, power drops drastically, and any variances that might briefly occur in fluctuation with fuel flow won't lead to any damage caused by temperature, or detonation. Detonation issues are critical at power settings above 75%, not below, and with loss of fuel flow, power drops and any attendant danger of detonation and associated damage drops with it.
Tatheplilt, having heard the testimonies and information from many pilots here more experienced than yourself, and having heard the recommendations from the FAA, including those posted in the practical test standards, why did you do that??
As the localizer starts to come alive fuel goes off. Normally around 2300' ish.
Is there any valid earthly reason why you would do this instead of setting zero thrust on one engine? Not only are you shutting off fuel below 3,000, you are doing it while flying an approach, descending. Not smart.
After he goes through his procedure fuel goes back on, zero thrust simulated. I feel that is the best way to go.
Why do you feel this way? Perhaps it's time for you to listen to virtually every other professional pilot in the business, the FAA, the industry, etc...don't try to reinvent the wheel. There's a reason that many of today's practices are conducted the way they are...because when it was done the way you seem to want to go, a lot more people got killed in training than in actual accidents. That's not right.
If the engine doesn't want to come back alive there is plenty of time to call home and talk about it.
You really think so? What do you do in the meantime if the other engine quits, or the student screws up and fails the wrong engine. Don't think it can happen? Think again. And don't do that any more.
Although my time is low, I'm very safety concious.
Possibly so, but it doesn't show. Don't try to make a name for yourself by reinventing the wheel, or you'll end up making a name for yourself...if you know what I mean. You don't have the experience right now to be innovative in trying what you think might be best or safest. Don't try. Stick with what is safest, and that is exactly what we've been talking about here. Simulate those failures on the approach with the throttle, set zero thrust, and don't go around on one engine. Land, taxi back, warm the engine up again, and go try it once more.