Ask a room full of BMW diesel owners which engine they'd trust with 400,000 km and you'll start an argument that lasts all night. One camp swears by the M57 — the straight-six that powered a generation of 330d and 530d saloons and refuses to die. The other points to the B57, the modern one, smoother and far more powerful, and asks why you'd live in the past.
Here's the thing the argument usually misses: they're both right. In our database, neither engine carries a single documented major fault. This isn't a fight between a good engine and a bad one. It's a choice between two genuinely excellent ones.
Quick answer: The M57 (84/100) edges the B57 (80/100) on our scores, and both are BUY-grade with no recorded critical faults. Buy the M57 for mechanical simplicity and cheap ownership; buy the B57 for refinement, power and modern manners. You can't really lose.
The legend: M57 — 84/100 (BUY)
Built from 1998 to 2012, the M57 is the engine that made diesel respectable for enthusiasts. Cast-iron block, conventional turbocharging, and an appetite for mileage that became the stuff of forum folklore. In our data it carries no documented major issues — the rare engine whose reputation for toughness is matched by the record.
What you're buying is honesty: an engine simple enough to maintain affordably, in cars old enough to be cheap, with a parts ecosystem that's been mature for a decade.
Found in: BMW 3 Series, 5 Series, 7 Series (525d, 530d), X5.
The successor: B57 — 80/100 (BUY)
The B57 arrived in 2016 as part of BMW's modular family, and it's a generational leap in everything except dependability — where it simply matches its ancestor. Up to 400 hp in the hottest forms, vastly quieter, cleaner, and more efficient. Like the M57, it carries no documented major faults in our database.
The trade is the modern one: more electronics, AdBlue/SCR emissions hardware, and tighter tolerances. None of it shows up as a reliability problem in the data — but it does mean a more complex car to own a decade from now.
Found in: BMW 530d, X5 30d.
And the one in between
Don't forget the N57 (78/100, BUY) — the 2008–2020 generation that bridges the two. Slightly behind both on our scores, but still a solid buy and far more common on the used market than the brand-new B57.
Old vs new, by the numbers
| M57 | B57 | |
|---|---|---|
| Years | 1998–2012 | 2016→ |
| Power | ~286 hp | up to 400 hp |
| Block | Cast iron | Aluminium, modular |
| Score | 84/100 | 80/100 |
| Documented major faults | 0 | 0 |
The verdict
The M57 takes it on points — but read that the right way. This is a four-point gap between two engines that both refuse to break. The score difference reflects the B57's added complexity, not any actual fault.
So choose by what you want from ownership:
- Want the cheapest path to a bulletproof BMW diesel? The M57, in a tidy E-class-era 530d or X5, is one of the great used-car bargains.
- Want modern refinement and have the budget? The B57 gives you 100+ extra horsepower and a far nicer car, with the same clean reliability record.
Curious how BMW's petrol six compares? See the B58 vs B57 showdown — petrol icon against diesel workhorse.
Scores are calculated from documented issues, repair costs, and failure patterns. Reviewed by the EngineScope editorial team. Methodology →