Diesel engines
The diesel engines are very economical and most of them are also powerful enough. So, they are really great until you get one of the 4 main scariest failures related to the:
- fuel system
- timing chain
- EGR system
- crankshaft bearings
To be fair I’m not saying that you will experience all of these issues, there are obviously exceptions and various variables.
Fuel system
1. HPFP (rare)
All of these engines are equipped with the infamous Bosch CP4 HPFP which can suddenly fail and release tiny metal particles into the whole fuel system – this is gonna destroy all the injectors.
However, this issue is not extremely common and it happens usually just in the eastern part of Europe and in the US because of the different quality of the fuel.
The HPFP can fail before 200 000 km, occasionally even before 150 000 km.
2. Injectors
Then there are the injectors which can fail mostly after 200 000 – 250 000 km. Usually you only get the classic faulty injector symptoms, but in the worst case – so not that often, the faulty injector can melt the piston or crack it. Especially cars with performance upgrades can more often end up with this kind of a major damage. By the way a faulty injector can also cause a louder rattling noise.
TIMING CHAIN
All of these engines are equipped with a timing chain which can fail.
In the older N series engines the chain can not only get worn and jump – possibly causing bigger or smaller engine damage, but it can also suddenly snap and definitely cause an engine damage!
N series engines – possibility of more worn timing chain or chain snap even after 150 000 – 200 000 km.
On the other side, in the newer B series diesel engines the chain is not known for snapping or premature failure. However, after 200 000 – 250 000 km it can be more or less worn as well.
A worn timing chain can make a noticeable rattling noise at engine start + possible rattle or whining/scraping noise at idle, but in many cases it won’t make any noise and that’s why it’s good to replace it preventively.
n47 timing chain noise on idle before and after replacement
EGR SYSTEM
Now let’s move onto the EGR system which can have 2 main issues.
1. Faulty/stuck EGR valve
A faulty or stuck EGR valve is nothing extraordinary. It can happen on any diesel engine and it will cause various symptoms like: uneven engine idle/shaking, engine stalling, increased fuel consumption, loss of power/limp mode, EGR related fault codes + also slight shuddering/jerking/kicking during acceleration. In many cases the EGR is only stuck so it’s enough to properly clean it, but in other cases you will have to replace it + on cars with vacuum controlled EGR sometimes just the vacuum line is damaged which can also cause these issues. EGR valve problems not pleasant but they are not gonna destroy your car.
On the B series engines the EGR was in a lot of cases replaced under warranty since in these engines it can fail even before 100 000 km.
video about EGR valve issues – turn on subtitles
2. Leaking EGR cooler (risk of fire!)
On the other side, the EGR cooler can start to leak coolant internally and this can contribute to a fire which will destroy your car completely!
Long story short:
All of these engines are equipped with a shiny metallic box on the top front of the engine which is the EGR cooler. The cooler can crack internally – thus allowing the coolant to leak into the internal parts of the cooler – after this the coolant will mix with the carbon sooth in the EGR cooler and it will also mix with the carbon sooth in the intake manifold (since over time the whole intake manifold gets covered in carbon sooth) – the carbon sooth is similar to coal so it can catch fire pretty easily which means, that if all the conditions are met – this mixture eventually catches fire. The fire will start in the intake manifold, first it will melt a hole in it and if you don’t interrupt this then the whole engine starts to burn and later the whole car.
Sadly, this catching fire is not some kind of a far away sci-fi urban legend. It happened many times in the past and even in the not that distant past, there are many videos, pictures and articles about the fires – EGR fire article, another EGR fire article. That’s why BMW already did a recall for this possible issue in the past, so in many of the affected cars the EGR cooler was already replaced to an updated part. Usually this would be the end of the story, but it’s not. Because in 2022 BMW introduced another updated EGR cooler. This means that even if your car already had a new EGR cooler fitted in the past – it can still catch fire since if the fix was made before 2022 then it’s not gonna have the newest updated EGR cooler from 2022. And actually, there is still an ongoing recall for this problem, so definitely check your car thru the official BMW website or call the dealer. And check it even if they already replaced the EGR cooler on your car in the past, since as I said in 2022 they introduced an updated newest EGR cooler. If your car is on the list then you will get a new hopefully finally good EGR cooler for free.
Either way you should not wait any longer and do something asap, because if your EGR cooler and intake manifold are full of carbon sooth and the egr cooler starts to leak or is already leaking then you are literally waiting for the fire to knock on your door/or hood.
CRANKSHAFT BEARINGS
The last main problem of these engines is related to the crankshaft bearings. There are many cases of worn main bearings and occasionally rod bearings in these diesel engines. The bearings can also suddenly spun – causing a big engine damage and even a seized engine = transforming it into scrap metal more or less. But before you start to panic I have to add that most of the documented cases are from the N57 6 cylinder engines. The 4 cylinder N47 engines can have worn bearings too but less often.
To top of that it’s good to know that before 200 000 km this failure is very, very rare, after 200 000 km the chance of this failure gets bigger and after 300 000 km it gets very high. On the other side I have to add, that there are also engines with 300 000 km or 400 000 km which still have the factory bearings. So, there are certain variables which can contribute to this issue, which means that not all of these engines are gonna end up with prematurely worn or failed bearings.
But either way, there is a pretty high chance that at 200 000 km mainly the main bearings are gonna be more or less worn to some extent. So, at this mileage point you should consider replacing the main and also the rod bearings preventively, because when you get a knocking noise from the engine then it’s already too late. Big or bigger damage is done and the only question will be if you need to replace “only” the crankshaft and the bearings or the whole engine. And when your engine seizes then you can of course throw away the whole engine.
Most of the documented cases are from the N series units, so it seems like the B series engines are not affected. Well, maybe. But I don’t really believe this, since the B series engines don’t have reinforced bearings and rare occasional failures are indeed starting to pop up in these newer engines as well. But again I have to add, that compared to the N series engines there are still barely any documented cases – the reason for this can also be the fact, that the B series engines are newer and still in most cases have less mileage.
The price for preventively replacing the crank bearings can be around 1 000 €, the price for replacing the bearings and the crankshaft will be higher approx.: 3 000 €, and when the shit really hits the fan then be ready to pay for an engine rebuild which costs approx. 4 000 – 5 000 €. Of course you can buy a used engine too which will be cheaper but riskier.
A specific louder knocking noise from the engine which will increase when you press the throttle is a clear sign of worn crank bearings. BUT there is an early sign of worn bearings too = metallic chips in the oil filter. So if it is possible, then before buying you should remove the oil filter and inspect it for metallic chips !
DIESEL engines other generic issues
There are also the other additional issues related to all the diesel engines so:
1. Crank pulley – The crank pulley on the front of the engine can crack and disintegrate, so check it
2. Coolant flange – All these engine have a plastic coolant flange mounted on the side which will eventually crack and leak coolant
3. Swirl flaps – The swirl flaps in the intake manifold are gonna clog up with carbon sooth, eventually they get stuck and the flap mechanism itself can get worn as well = causing various symptoms like rough idle, uneven engine running, check engine light. To top of that, on the N series engines the swirl flaps can rarely even break and end up in the intake channels ! So every 100 000-150 000 km you should check and eventually clean the whole intake from carbon sooth to keep the flaps moving freely.
4. Clean the intake ! – Every 100 000-150 000 km you should check and eventually clean the whole intake (the intake manifold and the intake channels) from carbon sooth. Not only to maintain good performance, but also to avoid the possibility of EGR cooler fire and keep the swirl flaps working properly. (carbon cleaning approx. 300 – 400 €)
5. Oil consumption – Excessive oil consumption can appear in all these engines. Rarely even after 100 000 km, but more likely after 150 000 km or 200 000 km. However, this is not extremely common and mainly engines with longer oil change intervals are more prone to this.
6. Glow plugs – The glow plugs will fail at some point causing rough idle after cold start and glow plug related fault codes. To top of that, replacing them in older or higher mileage cars is not gonna be easy since they like to get stuck, so it’s a good idea to replace them preventively every 100 000 – 150 000 km even if they are fine.
7. Turbo – Be ready that after 200 000 – 250 000 km the turbocharger will be more or less worn out. This is not that surprising, but some of the engines have two turbochargers which is gonna increase the repair costs.
8. Fuel in engine wiring – Believe it or not, all of these engines can have sometimes this interesting problem when a small amount of fuel leaks into the engine wiring harness. This can cause various symptoms and later a permanently damaged ECU, since the fuel will eventually leak into it. In most of the cases the main culprit of this leak is a specific fuel feed line which is connected to the high pressure fuel pump (part numbers below). There is a fuel sensor which is part of this line and this sensor can more often leak fuel internally into the engine wiring harness. So occasionally check the various connectors on the engine for traces of fuel and consider replacing that line preventively !
Fuel feed line part numbers:
Cars with N47 engine: 13538594893
Cars with N57 engine: 13538507686
Cars with B47 engine: 13538514092
Cars with N47 twin turbo engine (325d): 13538581793
Cars with N57 twin turbo engine (335d): 13538507687
Replacing fuel feed line approx.: 300 €
The fuel in the engine wiring harness can cause various electronic malfunctions. First they are gonna be minor and occasional like a check engine light, an occasionally drive train malfunction message and various engine related fault codes stored in the fault memory. But later it will cause a limp mode/loss of power, engine stalling, or the engine won’t start at all. In this later stage the fuel will reach the ECU and if you don’t act fast enough you will end up with a permanently damaged ECU.
At the dealer be ready to pay approx.: 2 500 – 3 000 € to replace the whole wiring loom with the faulty sensor, if your ECU is already damaged too then you have to obviously replace it as well and in this case the repair cost at the dealer will increase to approx.: 5 000 – 6 000 €. Obviously there are also cheaper alternatives: you can buy a used wiring loom and you can buy a used ECU as well, to top of that sometimes the ECU can be repaired
ON THE NEXT PAGE: TIMING CHAIN, TRANSMISSIONS, xDRIVE
