autoevolution
 

Here's Why BMW’s N63 4.4-liter V8 Engines Fail

Last year, we wrote a story about BMW’s N63 engines being a pain in the butt to run over a certain mileage. Back then, our info came from a BMW mechanic and we were amazed of the fact that only days after we wrote it, the Germans issued a sort of recall for them, to sort things out.
BMW G12 750Li 1 photo
Photo: BMW
Of course, this being the unit used on their most expensive models (excluding the M versions, of course), they were reluctant towards using the term: recall. Instead, they said this is a customer care package that would address some issues with the cars.

Long story short, customers were promised replacement vehicles of similar luxury and performance, while their daily drivers were in the shop, getting various parts replaced. Depending on the car, this could go from injectors and more complicated parts to the battery and timing chains. However, it still left us wondering what was causing the issue.

Well, as it turns out, now we know. It seems that in search of the best possible fuel consumption, some corners had to be cut and that left some issues behind.

One of the ways EfficientDynamics works is cutting down on alternator working times by recharging the batteries using regenerative braking or ‘smart-charging’ systems. These systems charge the battery when coasting and that might seem like a good idea at first but then you’d have to take into consideration how the car is going to be used.

If it’s going to be used in stop and go traffic, what good is it going to be? Well, not much and that started to show on a lot of cars. It’s not only that the batteries wouldn’t be recharged enough, it’s also that the systems on board are really hungry for electricity.

Another innovation BMW used for its 4.4-liter V8 is placing the turbochargers within the ‘Vee’ to save space and make the engines more efficient. The problem with that configuration is that they get very hot placed in that specific position and that means that they need to be cooled off after the engine was stopped. Guess how that’s done? Using the battery, of course.

Those elements lead to a quick depletion of the battery. Couple it with the problems in recharging it and you can easily see how they tend to fail after a rather short amount of time.

BMW did try to solve this problem by using expensive Absorbent Glass Mat (AGM) units that can handle the deep discharging and recharging processes more easily but that didn’t do much good either. In the end, they decided to change the batteries from 90Ah units to 105Ah ones and then they shortened the oil-change intervals from 15,000 miles (25,000 km) to 10,000 miles (15,000 km). What does that have to do with anything?

Quite a lot actually as their service bulletin now recommends that you replace the battery too whenever you change your oil. Being AGM units, they won’t be cheap to replace either. So, did BMW solve this problem on the new engines?

The question becomes rather important considering that the US will be getting the new 7 Series with a new version of the N63 engine in the fall. As a matter of fact, the US will only be getting two models at first, the 740i and 750i.

The 750i will be using what BMW calls a new 4.4-liter V8 only we know it’s the old one with a couple of improvements. Hopefully, they solved the issue by now either by making sure the alternator can keep a higher charge level for the battery or by some other means.
If you liked the article, please follow us:  Google News icon Google News Youtube Instagram X (Twitter)
 

Would you like AUTOEVOLUTION to send you notifications?

You will only receive our top stories