There's a huge difference between cruising at 80 in an aerodynamic sedan, and even CUV or pickup, and towing a box-shaped trailer or any trailer up a grade. Guys who have measured the F150 ecoboost intake manifold pressures report that at interstate speed cruising (steady-state), empty, the truck runs around 0 psi - in other words, no vacuum, no boost. It's as if an NA engine was completely wide open, but as there's no boost, the turbos aren't being worked. I hear mine spin up if accelerating on the interstate, but not under cruise, unless I'm towing, or climbing a hill.
When towing, it's a different story. It's on boost all day long. It sounds like the throttle is direct-driving turbo rpm. I get sick of hearing the dental drill in my head, even if it's soft, for hours.
So for an interstate rest stop empty, no big deal to shut it down immediately. For interstate towing, I learned a long time ago, the truck gets a lot hotter, everywhere. I've had pneumatic tubing melt underhood while at rest stops during heat soak.
Here's the fallacy - heat soak isn't done in 30 seconds. Heat soak goes on for 10-15 minutes. So the 30 second idle might take the edge off, but I really think 2-5 minutes would be more appropriate if you've worked the vehicle hard (again, even cruise at 80 isn't working it hard in this context). With a non-buffered heat gauge, you can watch heat soak after shutting down, and see the coolant temps go up 15-20 degrees after shutting it down, as the heat comes off the pistons, rods, crank, cylinder walls, etc, into the surrounding metal and into the coolant. IIRC, typical gasser piston/pin temps operate around 650F. Crank and Rods 300F.
It should also be noted that today's turbo engines use different turbo strategies than older. I'm not an expert here and only have article-reading to back this up, but older "blow-off" designs had the turbo spinning based on exhaust output. If you were operating at 1/3 throttle, turbo was engaged to the extent of 1/3 throttle. Newer designs use a TCV to bypass the turbo until the ECU deems that it's time, as to reduce pumping losses associated with adding extra hardware into the loop. So 1/3 throttle might bias the throttle to 60% open, but with no boost yet. This further reduces the time spent building boost, instead working as an NA engine for as long as the engine can meet demand, then adding boost in. Thus, the ECU intentionally reduces time on boost.
As I'm still learning this, it does make sense - there's no sense in having the turbo build boost at 1/3 throttle, only to have that pressure restricted by the throttle plate which would still be 2/3 closed. Pumping losses rise, would impact mpg, and there's unneccssary wear on the turbo. Using ecu-controlled TCV removes that conflict by biasing the turbo to work more only after the throttle is largely open. going back to the scenario above, suppose I'm highway cruising at 70 mph - that would mean the pedal is at 15%, the ecu is commanding 100% throttle opening, and 0% turbo involvement. At 40% pedal for a hill climb, the turbo may ratchet up to 20% boost, with the throttle plate at an unchanged 100%.
As I said, this last 2 paragraphs is still new info to me - if someone knows more I'd enjoy knowing - correct away!
