2019 RDX Turbo Question
 

Is it necessary or suggested to let the engine run for a few minutes before turning engine off to protect the turbo?. I can remember having a mercury Merkur 20 plus years ago and I had to let that idle for 2 to 3 minutes before shutting it down. My friend also has one of those ford RS focus (45K) and he says that all turbo engines require a cool down or I think he called it a spool down. Should I be doing this in the RDX

Not necessary. Most modern turbo engines have a mechanism that continues to drip some coolant from a small reservoir located above the turbo for a period of time directly onto the turbo after the engine is shut off. This keeps it from meltdown.

If a cool-down period was necessary, the owner's manual would state that.

I think it would be prudent to let the car idle after a hard run. But that is just me.
The Honda/Acura turbo is a new generation that ideally would not need the cool down. The RDX has water jackets in the exhaust manifold to keep the turbo running cooler than past versions. It does not need the 'gas dump' that old turbos used to cool so it also runs more efficiently.
Stuff like this is why I was not overly concerned with getting the turbo.

You never run it hard and put it away wet, whether is is a machine, or flesh and blood. Normal use, you just shut it off. Running it at 5,000 RPM? Let it cool down. Just one man’s opinion.

No you do not need to let it sit to cool down, turbos of today are WORLD'S apart from those of the 80's and 90's.

To restate and add to what's already been said...

1. Honda's current turbos are cooled using oil and water. Older turbos were cooled only with oil.

2. Page 519 of the Owner's Manual states, "When the engine is cold just after starting, avoid revving the engine or sudden acceleration."

3. There is no need for a "turbo timer" (a device or function that idles the engine to cool down the turbocharger). There is no caution regarding cooling down the turbocharger. Honda would have implemented either or both if they were necessary to ensure the vehicle lasted through its factory (60K miles) or extended (120K miles) powertrain warranty.

The reason I traded my NX F Sport for the RDX

The reason a "cool down" used to be recommended had nothing to do with actual cooling. The turbocharger got its oil pressure from the engine oil pump which only pumped when the engine was running. In fast driving the turbo spins at many thousands of rpm and the bearings can wear rapidly if oil pressure is taken away in that condition. By idling the engine a minute or so before shutting it down the turbo reduces its rpm to the minimum before oil pressure is taken away. I don't know if modern turbos have their own oil pump or if some other solution was found for the oil pressure issue. With the stop/start feature the manufacturer effectively took the idling before shutdown option away from the driver, so its apparently not needed any more.

An engine spins at many thousands of RPM. A turbocharger spins at hundreds of thousands of RPM.

A tiny, low-mass turbocharger like the ones in our RDX's can go from 0 to 200,000 RPM and back to 0 in a few seconds and is back at it's "idle" speed long before you can stop the vehicle and shut off the engine.

The only way a turbocharger will still be spinning at 200,000 RPM at shutdown is if you shut the engine off in the middle of a wide-open-throttle run.

The purpose of a "turbo timer", "run on", or "cool down" feature was to give a hot turbocharger time to cool down with oil still flowing through it so the oil didn't coke. Modern turbos are oil and water cooled.

That's just how turbochargers work.