That's a series of engines, not a single model. The FIAT FIRE [1] series has been in production for 36 years from 1985 to 2021 and, maybe you wouldn't expect it from FIAT, those engines were reliable.
The Jag XK platform had 45+ year run. I'd bet that as long as the 911 is made, it'll have an inline 6 and to someone's thinking it will be the same platform as the air-cooled version from 1964.
Engine architectures tend to last unless they are bad. They can do a lot on one also, the Toyota GR platform started out as a fairly vanilla V-6 but it has variations with GDI and variations with turbochargers and has been used a lot of different vehicles. A lot of different variations with different levels of compressions and such. It's basically the block and cylinders configuration.
I'll shout out the K-series though, it's a shockingly good platform. Lots of little details have been thought through, it's relatively simple, inexpensive and reliable and maybe one of the easiest engines to work on. If you were new to cars and wanted to start wrenching, the K-series is a pretty good place to start. It can take boost and make power and has lots of aftermarket support. I know civics aren't everyones cup of tea and it's not a big V-8, but I've yet to meet an engineer that isn't at least slightly impressed by the k-series.
Ah man, I owned a Jag XJS with the V12. Nothing on that car was what I'd consider 'normal'. Want to change the brake pads - down the rabbit hole I went. That car was why I own a voltmeter. I was a lot more knowledgeable after that car - smart enough to run, not walk from an XKE opportunity.
Came here just to rant about the FIRE and the Firefly.
The Multijet was also extremely reliable.
Instead, they were tossed aside to promote whatever garbage came out of citroen design centers, i guess to achieve the destruction of stellantis. (except in south america, they still get to use the Firefly)
In the couple years I've owned my (now) 10 year old wee-Fiat I think I've opened the hood once, when I first bought it, just to confirm the engine was actually there. Other than that, what engine?
Probably should pop it open (heh, Fiat Pop, no pun intended) to fix the headlight which has been out for about a year but it was a lot easier to get a (free) veteran's plate than poke around in there and you pretty much have to commit vehicular homicide in front of a cop to get pulled over with a veteran's plates so... I mean, it came with an extra headlight for a reason.
But, yeah, tiny little engine for a tiny little car which does it's job without issue, what's not to love?
I had the first Twingo model with that engine. Sure, reliability was exceptional, and it also felt nice to drive for a low power engine (55 HP). What wasn't exceptional however was fuel economy, which significantly increased the total cost of ownership of a car like the Twingo.
I think the car made it to almost 300000 km with the engine showing barely any sign of wear. Some parts broke down, and there was still regular maintenance, which, combined with poor fuel economy and state subsidies made it not economically viable to keep the car even though it still ran. The newer model we bought later didn't last as long, the engine was good but not as robust, but it was still worth changing because of fuel economy alone.
At no point we considered environmental factors, only cost, but they are tied, since better fuel economy means both lower costs and lower emissions.
So in the end, you we a engine that was reliable for sure but didn't meet modern standards in terms of running costs, emissions and performance. When the Twingo came out, the use of the Cléon-Fonte engine was generally considered a serious downside, and it was changed to the more modern and appropriate "Energy" engine shortly after.
Fiat FIRE engines are reliable workhorses, but they arent cool nor overbuild like K series. You can tune NA K20 to over 250 whp, or 400 whp turbo with _stock_ bottom end. Same reason 2JZ are legendary with stock bottom end good for at least 600 whp.
[1] https://en.wikipedia.org/wiki/Fully_Integrated_Robotised_Eng...