I wasn't saying the engine wouldn't warm up eventually, and I realized Dr. Bert is in a warm climate (I flew over Bakersfield in a small plane and wow! the thermal inversion over that end of the valley is bad!).
If I drove around in the desert all the time I might also remove my thermostat! If I drove the grapevine every day I would take it out for certain!
I was more concerned with short trips, you know the 5 to 10 minute trips some of us take frequently to the store and to work if the commute is short.

For several years I noticed my '79 300TD with a rebuilt '85 engine was real sluggish when I first started off in the mornings, we are talking even with 70+ degree ambient temps. Call it the "cold diesel." ALDA tweaked with little improvement.
I also noted that the temp gauge took longer to move to the operating temp (83C) where the heater would come on. I lived with this situation without digging into it for almost 2 years, because I swap cars and frankly the W124 300D came into my life (can you blame me for not wanting to drive the 123 when the '87 is beckoning? )
One cold day this winter I began to wonder why the '87 and the other 300D's warm up quicker on my 8 mile commute. In the "cold diesel" I never felt heat, or just started feeling some warmth as I reached my destination. I thought perhaps the fact that I had a three row radiator in it was involved, it always ran cold since I put it together (new engine and radiator all at the same time) so I finally mentioned it to my friend, a decades experienced shop owner and he said the car should reach 80C quicker that it was and that my car would run better if it got up to 80 quicker. OK, then with this info I decided to install a new thermostat (Kuhlermeister or Kuhlermaster brand) well, lo and behold the engine warmed up in 5 minutes and the car had more acceleration sooner! The diffrence was really noticeable after all this is my work car, I drive it almost daily so I know it is better.
I can assure you the old thermostat was bad. It had odd scrapes on the center brass shaft, I believe it was galling and sticking, making the warm up period much longer.
I can't say whether a cooler operating diesel will last longer but if you improve on the life of the OM617 you are potentially talking of raising it from 500K miles (I learned that from all the Ebay ads, right!?) to something I won't live long enough to experience.
ONe more thing that I believe is that frequent oil changes is one reason these engines last so long, besides good design and the forged iron head. I have seen two of my friends with Hondas and small Toyotas start buring oil at around 150K miles to the point they had to get rid of the cars. I looked at one of them and the EGR and PCV stuff was plugged with hard crusty carbon build up. I think that the small oil filters were part of the reason for premature engine failure but both instances they were not changing oil frequently and of course it was Dino oil. Oh no I am not steering this into a Oil thread. Forget what I said about Oil. this is a thermostat thread!

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

I certainly agree with you there. I never take these two for a 5 or 10 minute trip. That's what a gasser is for.

In Florida in Spring/Summer/Fall (they're all pretty much the same season....summer), I'm talking temperatures of usually high 80's to high 90's every day. Also, I've been driving it around with no thermostat in at all, only the seal ring, and it reaches 60-65C in very little time at all (granted, my cooling system is also functioning sub-optimally). And that's with NO THERMOSTAT!! Dokter Bert is only advocating drilling a hole in the thermo so it is open full throttle all the time.

It does seem like an appealing fix to thermostat problems (in the summer), and it will force you to change your coolant often when you put the new one in for winter.

And yes, any performance decrease caused by a slight drop in combustion (definitely not significant with only 15C difference) would probably be outweighed by a cooler turbocharger and hence denser air intake.

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"I would rather be ashes than dust!
I would rather that my spark should burn out in a brillaint blaze
than it should be stifled by dryrot.
I would rather be a superb meteor,
every atom of me in magnificent glow,
than a sleepy and permanent planet.
The proper function of man is to live, not to exist.
I shall not waste my days in trying to prolong them.
I shall use my time."

-Jack London 1876-1916

1983 300CDT (running WVO since 12/05)
1981 300SD (parts car)