If you’re thinking of going big, and I’m talking Rolls-Royce or BMW 760Li big, you’re probably not at all concerned about the problems we’re about to list about both the N73 and the N74 engine. However, if you’re buying a second hand BMW 7 Series or one of the Rolls models with this engine, listen up!
Doing proper research before you decide to spend a ton of money on a car is always a good idea. You just don’t want to end up with a lemon. And that’s why we are here to help you out.
First, we are going to learn more about the specs of the BMW N73 & N74 engines and then we are going to share with you the common BMW N73 & N74 engine problems. Lastly, we will learn more about the applications of these engines. So, without further ado, let’s dive into the topic.
Basic BMW N73 & N74 Engine Specs
The N73 engine is a V12 engine that was introduced by BMW in 2003. This engine replaced the M73 that was used previously.
The N73 engine was then replaced by the N74 engine, which is another V12 engine. The N74 is a further refinement of the V12 architecture by BMW.
What is worth noting about these two engines is that they share the same design principles. They are both V12 engines with a displacement that varies between 6.0L and 6.7L
Both of them are running DOHC design for the heads and use variable valve timing (VANOS),. The key difference between the two is that the older engine is naturally aspirated, while the N74 is turbocharged.
Understandably, the N74 creates a lot more power than the N73 engine since this forced induction really makes this massive engine alive.
Nevertheless, here are the specs for both of these engines.
BMW N73
- Configuration: V12
- Displacement 6.0L and 6.7L
- Cylinder Bore: 89 mm or 92 mm
- Piston Stroke: 80 mm or 84.6 mm
- Block & Head Material: Aluminum
- Head Design: DOHC
- VANOS: Yes, double VANOS
- Aspiration: Naturally Aspirated
- Turbocharger: No
- Direct Injection: Yes
- Horsepower: 439 – 453 hp
- Torque Output: 443 – 531 lb-ft (600 – 720 N-m)
BMW N74
- Configuration: V12
- Displacement 6.0L, 6.6L, and 6.7L
- Cylinder Bore: 89 mm
- Piston Stroke: 80 mm, 88.3 mm, or 90.4 mm
- Block & Head Material: Aluminum
- Head Design: DOHC
- VANOS: Yes, double VANOS
- Turbocharger: Twin-Turbo
- Direct Injection: Yes
- Horsepower: 536 – 624 hp
- Torque Output: 553 – 664 lb-ft (750 – 900 N-m)
Common BMW N73 & N74 Engine Problems
Common problems with the N73 and N74 engines include:
- Oil Leaks (Both Engines)
- Oil Consumption (Both Engines)
- Coolant Leaks (Both Engines)
- Turbocharger Failure (N74)
- Carbon Deposits (Both Engines)
- VANOS Failure (Both Engines)
- Timing Chain Stretches (N73)
- HPFP Failures (Both Engines)
We listed the common problems with the N73 and N74 engines together. Mainly because the problems are interchangeable. Both engines have similar issues.
So, now we will move on and further elaborate on these issues and learn more about them in detail. Knowing in detail when and how these problems appear is really useful because you will be able to learn how to avoid them. Let’s get started.
Oil Leaks (Both Engines)
Oil leaks are a common problem with both the N73 and N74 engine. These engines are made by BMW and if you are a BMW guy, you know that their engines leak a lot.
Most notable leaks develop around the valve covers. For those who don’t know, the valve covers are the two covers that cover the valve train. On this engine, you have two of them and both can leak oil.
There are also leaks from the timing cover, this cover understandably, covers the timing chain and uses a gasket material that can also degrade and leak oil.
Other leaks that can develop are from the oil pan gasket and the alternator bracket on the N73 engine.
Oil Consumption (Both Engines)
Another very common problem with both of these engines is the increased oil consumption. These engines are not serious oil burners.
But can consume engine oil. Oil leaks consume oil, valve stem seals can leak on some of these engines and burn oil.
And there is also the natural oil consumption that develops whenever these engines get a lot of mileage accumulated. So, for higher mileage engines it is practically normal to burn engine oil.
This is why we advise that you go for a lower mileage engine if you want to avoid these issues.
Coolant Leaks (Both Engines)
Coolant leaks are another common BMW engine problem that both of these engines have. These BMWs can lose coolant.
What is good is that these leaks are visible, if you check the engine frequently, you will notice that the coolant is leaking.
Also, the temperatures will rise if there is a serious loss of coolant. Common places that can allow coolant to leak on these engines are the radiator and the coolant hoses. But they can also leak from the coolant pipe under the intake manifold in the valley of the engine. Which can result in very expensive repairs.
Turbocharger Failure (N74)
Turbocharger failures were also noted on the N74 engine. The N73 does not have these issues mainly because this engine does not use any turbocharging.
But since the N74 engine has them, it is susceptible to turbocharger failures. The turbos can fail at 100,000 miles (ca. 160,934 km) and more.
When they fail, they can often leak oil, or produce whistling noises. These are the key signs that you have a blown turbo.
Not to mention that the replacement of these components can be somewhat expensive. This is why it is a good idea to rebuild them. Since there is nothing wrong with this procedure. The turbos will be good as new after refurbishment.
Carbon Deposits (Both Engines)
Carbon deposits are also very common on the N73 and N74 engines. So, what are carbon deposits, and why do they appear?
Carbon deposits are black deposits of carbon that stick to the intake valves. This is a common problem with many engines that use direct injection.
Both of these engines are using this system and they will require carbon cleaning every 60,000 miles (ca. 96,561 km) or so.
If you don’t clean the valves, the engine could have some issues down the line. Misfires, check engine light, low power, and eventually the engine head will fail.
And replacing these components is very expensive for these V12 engines. So, if there are carbon deposits, you need to clean them with a method known as walnut blasting every 60,000 miles (ca. 96,561 km) to be on the safe side.
VANOS Failure (Both Engines)
VANOS failures are fairly common in BMW engines and this engine is not an exception to this rule. This VANOS solenoid for those who don’t know is the variable valve control system.
This system helps in terms of efficiency and creating power from the engine. Unfortunately, it is pretty unreliable. Especially in the N73 engine. The components that fail are most often the variable valve control system solenoids that activate and deactivate the VANOS.
Replacing these components will solve the issues in many situations.
Timing Chain Stretches (N73)
Another fairly common problem with the N73 engine is timing chain stretching after 100,000 miles (ca. 160,934 km).
Whenever the chain will start to stretch, there will be a rattling noise that will develop behind the timing cover. Replacing the timing chain is a very expensive thing to do.
Make sure you address this issue as soon as possible.
High-Pressure Fuel Pump Failure (N73)
And the last thing to note is the high-pressure fuel pump on the N73 engine. This engine uses an HPFP for the direct injection system.
Inside this pump, there is a diaphragm that breaks off internally. And causes problems with fuel delivery. Replacing this pump will sort out the problem.
These replacements can be expensive, but it has to be done in order for you to solve this problem.
Which Models Have The BMW N73 & N74 Engines?
BMW N73 Engine
N73B60
- 2003 – 2008 BMW E65 760i/Li
- 2017 – Present Eadon Green Black Cuillin
N73B68
- 2003 – 2016 Rolls Royce Phantom
BMW N74 Engine
N74B60
- 2008 – 2015 BMW F01/F02/F03 760i/Li
N74B66TU
- 2016 – 2022 BMW G12 M760Li
N74B66
- 2010 – 2020 Rolls-Royce Ghost
- 2014 – 2020 Rolls-Royce Ghost V-Spec
- 2019 – Eadon Green Panthean Coupe
- 2014 – Rolls Royce Wraith
- 2015 – Rolls-Royce Dawn
N74B68
- 2017 – Present Rolls-Royce Phantom VIII
- 2018 – Present Rolls-Royce Cullinan
- 2021 – Present Rolls-Royce Ghost
FAQ
What are Common BMW N73 & N74 Engine Problems?
Common problems with these engines include oil leaks, coolant leaks, timing chain problems, oil consumption, VANOS failure, and carbon deposits.
How Reliable Are The BMW N73 & N74 Engines?
These two engines are pretty average in terms of their reliability. They don’t have serious defects, but they can leak fluids from everywhere, and this can be expensive to deal with in the long term.
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