BMW 48 volt mild hybrid system and X drive reliability

[jai_]

Hi I’m deciding between

BMW 330i 2.0 L B48 engine 254 BHP OR BMW M340 3.0L B58 369 BHP

All M340is after 2020 have this 48 volt mild hybrid system for emissions & come with X drive as standard. 330i is rear wheel drive and does not have mild hybrid.

I want to keep the car for many years so want it to be reliable. I believe they have similar fuel economy as the 3.0L engine does not need to work as hard.

I wanted to know if the 3.0L will be more reliable given that it has a larger displacement or will it be less reliable because it has this 48-volt mild hybrid system and x drive. So, more stuff to go wrong? I have seen there is a class action lawsuit in the US RE the X drive transfer cases failing.

I cannot see many documented failures online on the 48 volt mild hybrid. But could this be because its too new as its only been out since 2020? I can see that Audi have been having some issues.

https://g20.bimmerpost.com/forums/attachment.php?attachmentid=3154671

• This topic was modified 3 weeks ago by jai_.

[admin]

Hybrid systems are generally very reliable (especially Toyota and Honda) and mild hybrid systems (48V) offer typically 5-10% fuel economy benefit. Full Hybrids offer much more fuel economy benefit. The other advantage of a mild hybrid is that the fuel saving stop/start system doesn’t use the noisy starter motor, it uses the hybrid alternator which you generally won’t even hear or feel it restart the engine. All wheel drive generally will cost you a couple of MPG compared to just rear wheel drive. In general the 4-cylinder turbo will yield significantly better fuel economy than the 6-cylinder. As far as the 3.0 engine not working as hard, that is not an issue for normal driving because the average power needed for cruising is only a tiny fraction of peak power for either engine. Overall the X-drive mild hybrid will be roughly as fuel efficient and just as reliable as the 330i, though I do not know if the transfer case is still an issue. The 330 mild hybrid will be the most fuel efficient choice.

[jai_]

Hi thanks for your response.

But would the cost to replace 48-volt mild hybrid battery and other systems such as starter generator, dc/dc converter outweigh the fuel savings if keeping long term?

I appreciate that the Japanese are ahead with hybrid technology but unsure how the German brands stack up in comparison.

Would you say that the full plug in hybird (BMW 330E) is equally as reliable as the 48-Volt Mild hybrid M340i. Or will the plug-in hybrid have more costly repairs in terms of what can go wrong/battery replacement. I’m guessing that the plug in hybrid will have best fuel economy.

[admin]

The Hybrid system batteries, electronics, and motor are extremely reliable and durable. The batteries are usually Li-ion which have huge lifetimes. My son has a Prius with more than 300,000 miles with the original everything except rear wheel bearings. The starter/generator is more robust than an ordinary alternator. A full or plug-in Hybrid will have better fuel economy than a mild hybrid by a large margin. The disadvantage of a plug-in over a regular full hybrid is the added size and weight of the battery pack. Every vehicle that is available as both a plug-in and a non-plug in hybrid sacrifices cargo space for the larger battery. The full plug-in Hybrid BMW 330 should be as reliable as the mild-hybrid M240i and has the advantage of a pure-electric AC compressor (no belt or clutch). Take a look under the hood of a Toyota, Lexus, or Honda/Acura hybrid (except for some of the trucks and large SUV”s) and you will see that there are not even any belt-driven accessories. Also their transmissions are super simple and robust.

[jai_]

Thanks Dave also;

1) Do you think full EVs have the same reliability as you described with plug in hybrids and other hybrids?

2) Is it a myth that plug in hybrids or any other hybrids may harm engine health due to the constant switching between the engine and the battery causing engine to be hot/cold.

3) If we were to compare a 330e plug in hybrid and 330i petrol which would be the more fun to drive ( as I know you believe cars should be fun 🙂)

330i 254 bhp 400 nm torque 400 nm torque, 1470kg
(Weighted fuel consumption = 41.5 mpg)

330e 288 bhp 280 nm torque, 1910kg
(Weighted fuel consumption = 39.8 mpg; 63 mile range)

[admin]

The main problem with EV’s is their mass. They are typically 40 to 50% heavier than a similar ICE or hybrid vehicle. Weight is the enemy of everything a car needs to do: acceleration, braking cornering, responsiveness. Remember that acceleration is not proportional to engine power or torque, it is proportional to the power / weight ratio. note that engine torque is meaningless. From my POV, fun-to-drive is inversely proportional to vehicle mass and proportional to the power/weight. EV’s should be more reliable than hybrids since the powertrain is really simple, but many brands/models of EV’s have less than stellar reliability results. I assume that is partly due to the newness of the manufacturing processes, and should be rapidly improving.

It is true that plug-in or full hybrids can let the engine temp drop fairly low during ordinary driving (depending on traffic conditions) when the system switches to electric drive or regen, and that adds some thermal cycles to the engine, but that is not a real issue for engine life and durability because the shut-downs and cool-offs are less damaging than idling. A hybrid hardly ever idles and idling (as I have written about here “Idling”) is tough on an engine. Also, the hybrid systems limit the amount that the coolant temp can drop in cold weather because the powertrain computer prioritizes having enough coolant temp to keep the cabin warm.

Regarding the fun to drive question, compare the vehicle masses and Power/weights. The lighter vehicle should handle better and feel more agile and the lower Kg/HP vehicle will accelerate faster.

[jai_]

Looks like hybrids more proven technology.

At what MPG would you consider is fuel efficient?

And at what kg/bhp would you say is considered slow and fast ?

[admin]

Difficult question to answer, you just have to compare similar size cars fuel mileage and acceleration times. For example a Toyota Camry Hybrid will get about 50 MPG city and Highway, the Accord Hybrid in top trim level gets about 45 MPG. My experience is that all BMW’s are relatively fast. Any car that does 0-60 MPH in less than 8 seconds is fast enough for every-day use. Overall, it really depends on what you are used to and how aggressively you drive.

[gero]

I’ve noticed the transition is nearly seamless on the highway, but around town it sometimes shudders at low speeds. My dealer said a software update helped smooth out the engagement logic. Overall, the fuel savings on long trips make the occasional hiccup worth it.

[Author]

Posts