I don't know why the engine isn't heating up- I suspect it has to be some kind of flaw as it is certainly not universal.
My car heats up somewhere between 55c (outside temperature ~10f) to fully (90c) during my drive from my house to my breakfast haunt, which is a 1.2 mile drive along mostly dense residential streets with several crossing guards and stop signs and strictly enforced speed limits between 25-35 - (there are three schools along the route) I usually average between 17 and 19 mph according to the trip computer.
I do not warm up the car at all or in any way. I turn it to "on" and set up my built in Nav, set my dash Mounted Garmin to speedo mode, set the transmission to economy, adjust climate controls to cold start setting (72f, fan 2.5, all three vents, rear def if needed), and plug in my phone and set up the stereo. And then I start it.
I back out of my driveway and let the car control everything on my drive- this is usually pre coffee, so I am too asleep to do anything but watch for children walking to school.
By the time I drive down my einbahnstrasse to the stop sign (about 200 feet), turn left, and and drive about another 600 feet to turn left again, my auxiliary heater is pumping out heat. By the time I get to my breakfast place it is almost always at 60c or higher, so I feel fine shutting it off and sitting while my wife grabs breakfast and then eating it- it almost never gets cold enough to start the car again before we finish breakfast, in fact. It's ability to stay warmish for hours is a noteworthy feature in fact.
Further two notes- I rarely wear a jacket to the car, and it gets so warm so fast, I never wear a jacket driving, lest I end up like Del Griffith in Planes, Trains, and Automobiles.
It is presently cloudy 49f and breezy near a lake as I type this. I shut off the car two hours ago. I am wearing a short sleeve t-shirt and overalls. I am slightly on the warmish side. If it was a cold day (25 or less) this is usually the time period where I start thinking about breaking out my jacket. It's usually 3-4 hours before I break out my sleeping bag.
So no, very seriously, not all Metris vans have temperature issues. Mine sure doesn't.