How do modern cars regulate temperature so well?

As others said, until the import manufactures brought their well engineered cars over, all the public knew were the basic engineered cars the big 3 were pumping out. If you’ve only had ground beef (big 3 cars in the last century) that’s tastes pretty good. However if you’ve also had beef tenderloin, only then will you realise there’s better tasting (better engineered cars) beef available.

Back then cars overheating going up a slight hill on a hot summer day was normal, the public thought that was part of driving a car. Until the import cars starting coming over, it was just expected overheating was part of car ownership even without pulling a trailer.