Back in the day, when I first started driving and therefore buying / selling / wearing out vehicles, we made a distinction between the size and type of motor and the expected lifetime.
Big V-8's were expected to last longer than inline 4's, although there were not a lot of inline 4's available to buy. Inline 6's were considered more-or-less bulletproof ... GMC 194's, 230, 250's; any Chryco slant 6, the 300 Ford's, etc.
The smaller motors became more reliable as carbs were replaced with Fuel Injection, while the bigger motors became less reliable as they moved from cast iron to aluminum blocks. Early aluminum heads were iffy but that was figured out pretty quickly in most cases.
I've sent more than one vehicle to the wreckers with 200+K miles on the clock ... worn out completely, windows won't crank, seats showing springs, parts falling off and not being replaced, on their fourth fuel pump and fifth alternator ... but with perfectly purring auto transmissions and motors.
Carb-equipped vehicles were at the mercy of winter. Fuel Injection has almost single-handedly doubled or tripled the life of motors when sub-zero temps were the norm for half the vehicle's life. The wear at startup with the choke was severe (manual [early 1960's] or automatic [late 60's] chokes, you gave up easier starting for higher engine wear. Manual started easier but dumped more raw fuel into the cylinders, past the rings, and into the oil).
We used to peg the useful life at around 120,000 miles (180,000 Km). Today it's double that, under severe service, and often more.
