What was/is the most reliable IC engine of all time?

for OHC V8s the Mercedes M113 for sure, really only let down only by the vehicles it was installed in.

it requires significantly less maintenance than a toyota UZ or any other comparable engine
 
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In that case, the BMW N54 and N55 also should make the list of reliable motors.
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No, you need to re-read my comment (and think about it this time).

Anyone can make a crappy motor, turbo or non-turbo. The highest mileage over the road vehicles (tractors) all have turbos and were properly engineered as such. BMW has made some HORRIBLE engines, both turbo and non-turbo (and they are not alone among manufacturers).
 
Ford 3.0 OHV Vulcan Engine.

Spock

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The Big Three straight sixes all qualify.

Ford was still offering versions of the six as an industrial engine long after it was discontinued in the light trucks. When I worked in corrections, we had a "tug" built in the early '00s that had one as power. No, smart mouth, I don't mean 1900s either. :D
 
GM's 2.5L 4-cylinder Iron Duke . Did nothing well , reliable ran forever in any condition, good emission and basically a golden TURD.
I know I owned one only because I wanted my own engine and transmission in a 82 Camaro and the Iron Duke was the cheapest option. So I ordered the Z28 suspension on a base RS Camaro with the Iron Duke engine and saved I think about $6000. And then built my own engine and transmission to install in it.
 
No, you need to re-read my comment (and think about it this time).

Anyone can make a crappy motor, turbo or non-turbo. The highest mileage over the road vehicles (tractors) all have turbos and were properly engineered as such. BMW has made some HORRIBLE engines, both turbo and non-turbo (and they are not alone among manufacturers).
If you really think about it (and I mean give it SERIOUS consideration), any engine can be considered "reliable".
Just because you think BMW made "horrible engines" doesn't mean everyone agrees with you...that's just your opinion and I'd consider you lazy/incompetent for not being able to perform regular maintenance according to BMW specifications.
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4.7L Toyota V8 would be my choice. But others have their favorites.

https://www.motortrend.com/features/million-mile-tundra-the-tear-down/
Another UZ vote from me.

Lots out there with long lives too. Just my personal experience with cars in our family....(experience that others can & will mimic with their vehicles regardless of make)
Dad put 385k on the 305 in his 77 Camaro. Gutless & drank oil like kids guzzle Kool-Aid, but it ran & ran & passed CA smog over & over
Mom has 185k on her 96 s/c Riviera. Doesn't see much use the last 5yrs but never an issue from it.
Brother has 188k on his 3uz, but that's not much.
Dad had 315k on his 99 rx300 when it died last month.
351k on my 1uz
287k on gf's dads 2uz
250k on the 3.3 in our 89 Buick Century family car growing up.

I love these threads & reading everyone's opinions & experiences (not sarcasm 😂)
 
yanmar and kubota make/made some pretty reliable engines. ford 300 was my favorite for a long time as well as the dt466
 
GM's 2.5L 4-cylinder Iron Duke . Did nothing well , reliable ran forever in any condition, good emission and basically a golden TURD.
I know I owned one only because I wanted my own engine and transmission in a 82 Camaro and the Iron Duke was the cheapest option. So I ordered the Z28 suspension on a base RS Camaro with the Iron Duke engine and saved I think about $6000. And then built my own engine and transmission to install in it.
The longest lasting engine you wished would die sooner? My buddy had a manual S10 with an iron duke and it was remarkably bad in power, torque and NVH, but it never quit with all the hateful abuse he could throw at it... Kind of like how terrible tires seem to last forever too.

For little gas 4 bangers the ford/mazda duratec seems to be pretty good. I did a 2-1 shift instead of 2-3 shift on the autocross course and it probably saw 9k rpm atleast and just sucked it up and kept on going... I could be wrong, but I don't think to many engines can shrug off 50% more rpm over redline?
 
My very first car was a 72 Pinto that was given to me by my uncle. The only internal work the engine I think it ever saw was some new umbrella type valve seals as it consumed a couple of quarts of SAE30 between changes. I sold it with ~300k to an old iron worker in our neighborhood who drove it for many years.
 
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