M54B25 vs. M54B30 reliability

[jonnyd42]

I know that these engines don't share 100% of their parts. I'm curious if anyone can speak to the differences in terms of reliability, and which part differences cause this. We have a car with each:

e85 Z4 w/ M54B25: 70k miles and no problems
e60 530i w/ M54B30: 170k miles and no major problems - small oil leak

[MauiM3Mania]

Moved from the General BMW Discussion sub-forum.

[bmwdirtracer]

The engines are going to have the same longevity as one another, Therefore, the E60 has used up 100k more of its engine life, IF THE MAINTENANCE HAS BEEN THE SAME ON BOTH CARS.

The E60 has more computers, and far more gizmos to fail.

To counter this, the Z4 has a convertible roof, which I consider to be nothing but trouble. The motor sits in a bucket which collects rainwater, the roof leaks and makes the interior moldy and unpleasant, and you've got a huge steel frame an inch from your head, which is bound to be "uncomfortable" if you're ever in an accident. And, well, getting in and out of the car is a royal P.I.T.A., too.

But your question, I guess, was whether the B30 or the B25 was more reliable....and I'd say again: With the same mileage and same maintenance, there is no difference at all.

[shadowpuck]

+1 - agreed with Chris. that sums it up very well.

[mry82]

I'm no expert and this is mostly hearsay, and heard it through the (forum) grapevine kinda info, but it SEEMS like way more people have discovered oil pump nuts backed off on 3.0s vs. 2.5s... Opinions suggest that some specific vibration frequency, associated with the longer stroke and high rpms, contribute to the failure (apparently a significant number of people have found the nut loose enough to remove by hand, or it basically falls off when touched)... You can DIY or buy a pump nut with safety wire, so it cannot fall off, but the oil pan has to come off... That's labor extensive, expensive, or both depending on who does it... I THINK I have read of a few failures on 2.5s, but at least one was a tracked car. If high rpms are not sustained for long periods it may not even become an issue, but it is something to think about on older high mileage cars!

Rather than droning on more about something I don't really know about, or have firsthand experience with, I will just recommend searching for the issue if it interests you... If it were as common as some of the threads suggest, I would think Chris and others would have seen it more often, and I'm not sure if Chris has seen this happen at all...

[bmwdirtracer]

Nope, never have, my friend. Now, if we're going to talk about what kills M54's....that would be overheating.

Oil pan gasket is a 5 or 6 hour job. In an extra 5 minutes, you can make sure the nut is snug, and use a punch to lock the threads against the nut. Or spot weld the nut to the gear, better yet.

Certainly, when I rebuild any engine, I use red loctite on the oil pump nut,,,,and the I spotweld it, because I'm anally retentive.

Just because you're paranoid doesn't mean they're not out to get you.

[mry82]

Haha, indeed. It is comforting to know you have not seen this problem... I like that.

That was the only difference I could remember having read about, between the two engines... I THINK BMW started using loctite somewhere along the way, at least on the ZHPs... time makes my memory fuzzy... Wish they had done that from the start; makes sense the factory didn't weld it, so it was more serviceable, but a little loctite seems easy enough (and welding makes sense if you are in there anyway!)... Hard to imagine BMW engineers aren't thinking about what is best for 2nd, 3rd, and 4th 200k+ mi owners, eh?

I will admit I used to wish my car was a 3.0, and this made me feel better about having the 2.5... just like the subframe issues made me feel better about the AWD (the 38/62% front/rear torque bias helped too)... That's what you get for buying a BMW as your wife's snow car and then deciding to keep it (she has a subie now, I just didn't want to part with the e46)... I guess AWD would add another hour or two to that oil pan job...

Chris, did you get a Mercedes?

[bmwdirtracer]

My step mom died, and left me her E500 4-matic. so I have a new winter car, and am looking to sell the Subie. I bought the Benz a brand new set of Blizzaks, so it'll get me home in the snow.

[mry82]

My condolences Chris.

Too bad we bought the Legacy already; I would have been interested in a car you'd been maintaining. Best wishes.

[MarcoZandrini]

Chris, you have my sincere condolences.