Here’s a thought, maybe the poster was responding to the OP about cold temperatures and not you.
But about your post and the heat, I’ve had a few motors not wanting to start when they are hot. I was told vapor lock on some of the older ones.
Posters beowulff & Toledo Jim have expertly addressed the technicalities.
But what you probably meant in layman language is that modern oils are thinner at any given temp than were 1960s oils. And the difference is bigger when cold than when hot. Which is helpful for cold starts. That’s all generally correct.
Overall we have several folks talking about “hard starting”. It’s useful to distinguish between “cranks weakly” and “takes more cranking to light off” and “idles crappily at first”. Those are different problems with different causes and solutions. Though all are typically made worse by serious cold.
It’s also clear-cut that “cold” in Thailand isn’t anything of the sort. 
A car that has hard-starts when warmed up has a mechanical or electrical problem. Vapor lock in ancient vehicles, failing ignition modules or sensors in newer ones, lousy compression (exacerbated by thin oil at temperature), etc.
true, but on a modern (e.g. 2008+) diesel, starting at those temps is usually nothing more than a few attempts at cranking. old ones were like swearing at it for half an hour, then saying “welp, time to bust out the ether.”
all diesels are fuel injected, that’s crucial to how they work.
ah. you’re comparing the old 7.3 liter IDI to the 7.3 Powerstroke. Despite having the same displacement, they are two totally different engines. the 6.9/7.3 IDI was a mechanically governed engine with a “low” pressure (2,000 psi) injection pump, pre-combustion chambers, and effectively zero electronic controls. the 1994 7.3 Powerstroke (Ford’s branding for the Navistar T444e) was an electronically controlled, drive-by-wire, direct injection engine with high pressure (20,000+ psi) electro-hydraulic unit injectors.
I had an F-250 with the 6.9 IDI engine; those trucks had a fragile, failure prone glow plug controller. if it failed (either by not working or getting stuck and frying the 6 volt glow plugs) that truck was impossible to start when cold.
Ford muddied the waters a bit in 1993 and 1994 by offering a run of 7.3 IDI engines with an ATS turbo kit installed for some silly reason. I know they were trying to use up their remaining IDI engines but the turbo kit only added (not joking) 5 horsepower.
Thanks
I stand corrected.
Strange in that the turbo version in 1994 only added 5 horsepower officially . I drove both the non turbo and the turbo version and the one with the turbo was significantly faster (more than the 5 hp indicated - probably closer to 40 - 50 hp by the seat of the pants testing, although it may have been the later T444E version
Or in other words I could get the non turbo version to 95 mph max and the turbo version to 115 mph max (no speed limiter in either that I could tell) and the trucks were otherwise configured exactly the same (extended cab - long box)
if the fender badge said “POWERSTROKE DIESEL” then it was the new one. if it just said “TURBO DIESEL” it was the IDI. The Powerstroke was also a lot noisier due to the return to direct injection.
I just don’t think they could really have wrung more out of the IDI; it was already at 21:1 static compression ratio and fuel burn was limited by the poor atomization of the low-pressure injection and the turbulence in the pre-chamber.
I took a recently purchased four-door 'Vette back home to Indiana from south Georgia once around Christmas '88. I had just put in new 20w-50 oil and a new filter. By the time I got there, it was -15 F outside. I went out the next morning to start it, and the starter only manged a half revolution of the engine. I pulled out the dipstick, and oil came out with it, much like stringy mozzarella clinging to a slice of pizza. A quick trip to the local hardware store in my dad’s car allowed me the purchase of a dipstick heater which after twenty minutes of use let the car start right up. A trip to my brother’s house (he had a heated garage) and four quarts of 10w-30 solved the problem.
Some of this I knew; some I had forgotten.
I got to wondering because a few days ago, on the first really cold morning of the season, my car was noticeably sluggish in starting. The battery was getting pretty old, so I went ahead and replaced it.
That’s a good idea. Usually after a hot Summer the battery had taken a beating. Working as a mechanic, I’ve replaced batteries and starters at the end of Summer/start of Winter.
Being a ski bum for some years, I can say that if a car is hard to start, taking in the battery the night before greatly increased your chances of not having to hitch to the slopes the next day or bum a jump. When I removed the battery for the night and put it back i when I needed to go it never failed.
consider the fact that modern cars are way better than those immense pieces of shit we had back in the 1960s.
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That particular 1994 F250 truck with the turbo did said “Turbo Diesel” I could get up to 110 - 115 mph (Only tried it once - seriously ).
I also drove a later 1995 F250 truck with the Powerstroke diesel in it and that one could also max out at 115+ mph (only tried it once) and it felt like it had more power than the Turbodiesel.
Unfortunately, after that, we started to use Dodge trucks (Great for their Cummins Engines but the transmissions and bodies were not as good as the Fords until the later model years say 2004+)
Note that both the Turbo and the Powerstroke trucks took a long time to wind out once past 100 mph and there may have been either a wind assist or a slight downhill helping as well as being in the middle of winter (cool dense air - more power!! - although it was only a few mph extra in the winter_
Now that I remember this better the top speed I got out of the turbo was closer to 110 mph and the powerstroke was a little past 115 mph but I only drove those 2 trucks maybe a total of 1000 miles compared with the non turbo 1994 F250 that I had over 200 000 miles on it (in addition to the idling) when we sent it to auction (and was still running good after we rebuilt the heads from the excessive idling.
Also, there were times when we ran these pickup trucks for 2- 3 weeks without ever shutting them off except to change the oil in the winter.