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

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As far as common gasoline engines go, the 2 valve Ford modular engines are among the longest lasting when "real work" is required of the powerplant. Toyota V8's also last. It was very common for local modular powered delivery vans to reach 900K abusive miles. The best 5.4 I know of was 1.2 million miles.

I know there is a lot of love for the classic six cylinder engines, but they did not really last as long in actual use as the modular engines did. In our ladder, work and small crane trucks, the six cylinder classic engines really struggled to make the miles. And in our sister company's delivery service, the replacement of the sixes with the modulars was a huge step forward in engine lifespan.

Something to keep in mind, the Ford modular truck version of the engines had more robust connecting rods, with full floating piston pins and much tougher pistons, equipped with thin, full tension, hard chrome faced rings. The block is a unique very high quality cast iron (very low wear rates) and was designed to be very dimensionally stable with it's deep skirt design. It's no surprise they last so long, they are very, very well made to do so.

The secret to long modular engine life was really simple, regular oil changes with a quality oil of sufficient viscosity. It should come as no surprise the 1.2 million mile van used 10W-40.

So, that's my vote, Ford's 4.6 and 5.4 2 valve, modular TRUCK engine.
 
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Buick 215 V8. All aluminum, developed in the 50's, put into production in the 60's. Rights purchased by British Leyland who continued to build and enhance the engine until it's last gasp in 2004. Sure, the Brits ruined it with the electronics however the basic engine is almost impossible to kill.
head gaskets can’t take any overheating, wet intake, cams and rocker arms made of cheese. the overbore engines had block cracking issues.

at 200k miles they are already tired but it’s pretty remarkable an engine originally designed for throwaway 60s compact cars could even get that far. every buick small block that came after followed the 215 pattern.
 
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I have to recommend the 4-cylinder 1.9-liter VE TDIs sold by Volkswagen from 1996 to 2003 (in the US).

The cars themselves are rusting away but the engines seem to last forever. Even a rusty one with 300k-400k mile but good maintenance records can sell for $2500 in the current market, while nice ones sometimes $6,000-$8000. These were cars that cost around $17,000 when new.
 
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Some good entries and I don't know the answers but I see some trends.

I didn't see anything modern, or Audi, or BMW, or VW, or Benz listed. I might have overlooked it, but so much for "German engineering, overbuilt, blah blah blah."

If I were an engineer making the best engines I could, I would take a list such as this, take the best elements of the best most robust engines made, and simply improve upon them where necessary without any major redesigns which might make the design not as good.

And this puzzles me. Why do we have so many poorly designed engines, transmissions, and widgets in the world when we know what truly works and what does not, yet we seem to continue to try to make junk when the formulas have been nearly perfected?
The VW 3.6 is pretty solid, and we can't forget the old 2.0 (naturally aspirated). Other than that most of their turbo offerings have had a checkered past. They have been updated and improved upon over the years and they make some of the best turbocharged 4 cylinders in the industry IMO. However, to expect 250K+ trouble free miles like an old Honda / Toyota N.A. 4 cylinder is rational. There's just a lot more going on under the hood.
 
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Honda XR400R
For over 12 years I have been beating on my 2003 model in hot dusty gnarly conditions and it still runs perfect. No oil leaks, no oil consumption, no weird noises, starts easy, good power, etc. I bought it used and by this point I would expect some signs of wear but I don't see any. It gets normal maintenance only. Pretty amazing really, especially for an air-cooled engine that sees a lot of low speed, high stress conditions. I guess it has a few things going for it... large oil capacity, oil cooler, relatively low compression, no emissions equipment, plus it's a Honda.
 
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I think it's easier to find specifically terrible engines than good engines. There's been a ton of great engines in the last 30 years. I think the pinnacle of reliability is stuff developed in the late 80s/early 90s. Manufacturing processes were really tightened down, but they really didn't make enough power to hurt themselves or wear themselves out.


As far as common gasoline engines go, the 2 valve Ford modular engines are among the longest lasting when "real work" is required of the powerplant. Toyota V8's also last. It was very common for local modular powered delivery vans to reach 900K abusive miles. The best 5.4 I know of was 1.2 million miles.

I know there is a lot of love for the classic six cylinder engines, but they did not really last as long in actual use as the modular engines did. In our ladder, work and small crane trucks, the six cylinder classic engines really struggled to make the miles. And in our sister company's delivery service, the replacement of the sixes with the modulars was a huge step forward in engine lifespan.

Something to keep in mind, the Ford modular truck version of the engines had more robust connecting rods, with full floating piston pins and much tougher pistons, equipped with thin, full tension, hard chrome faced rings. The block is a unique very high quality cast iron (very low wear rates) and was designed to be very dimensionally stable with it's deep skirt design. It's no surprise they last so long, they are very, very well made to do so.

The secret to long modular engine life was really simple, regular oil changes with a quality oil of sufficient viscosity. It should come as no surprise the 1.2 million mile van used 10W-40.

So, that's my vote, Ford's 4.6 and 5.4 2 valve, modular TRUCK engine.

The original engine in my truck (01 5.4, 2 valve) died at 58000 miles. Someone dumped a bunch of washers down the air tube. They don't like that :D

Apart from a leaky head gasket, its replacement is still pulling trailers at 238000 miles! It gets worked , too. This last weekend it pulled the Jeep through some hilly terrain and spent a lot of time at 4000 RPM pulling hills. They seem to enjoy being abused.
 

wdn

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The most reliable engine of all time is the Toyota 2UZ-FE in the Gen 1 Tundra, Sequoia and Land Cruiser. That is the engine in the one million mile Gen 1 Tundra that still had its original engine and transmission, with no rebuilds of either.
 

OVERKILL

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The most reliable engine of all time is the Toyota 2UZ-FE in the Gen 1 Tundra, Sequoia and Land Cruiser. That is the engine in the one million mile Gen 1 Tundra that still had its original engine and transmission, with no rebuilds of either.
The 5.4L in the Million Mile Ford Van would like a word. Trans lasted 1,211,950 miles as well. This was of course a cargo van, hauling deliveries for that mileage.

Unfortunately, as the site shows, the old girl lost oil pressure just a hair below 1.3 million miles (1,299,986 miles).

If we are allowing diesels, here's a 1.3 million mile 7.3L PowerStroke backed by its original transmission too:
 
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Inline 6-cyl engines are underappreciated. They are the smoothest, most naturally balanced, vibration-free engines that can be built. The only engine smoother is the V-12, which is two inline 6 engines put together.
I'm quite partial to the AMC 4.0l straight six. I have seen many go very far over 200k. I'm not saying that its the most reliable engine ever, rather the best engine I've ever had.
 
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Anything with a turbo


....my mistake, I thought you were asking for the least reliable engines of all time
The Saab 900 4cyl turbos would run 100’s of thousands of miles with reasonable care. It was the first reliable turbo IMO.
 
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