BMW E90 N52B25 Engine Rebuild Break-In Procedure & Oil Consumption

[ace309]

I recently rebuilt a 2005 BMW E90 N52B25 engine (EU spec) as it had bad compression on cylinder 6 (was a hole in the valve). Tore it all down, had cylinders measured and block honed, did a valve job and replaced new valve stem seals as they were hard as a rock. Pistons rings were well out of spec (almost double) so measured and replaced them with new rings and very happy with the clearances. Crank & Conrod bearings were in great condition so I reused them and were well within spec as engine had 2 new pistons for some reason, so I assume at some point the engine had been previously rebuilt. I replaced the CCV (under intake) and all hoses with new ones even though there was very little oil in the intake and everything looked fine when I took it apart.

I read online, the engine break-in procedure says do not exceed 4500rpms or 100mph for first 1200miles: I started the car, let it warm up for 5 minutes, put a brick on the accelerator to about 1500-2000rpms for 15 minutes until the fans came on, shut it off, let it cool down and did this again. Then drove it around gently with low rpms around town, checked for leaks, and drove it on the highway everyday gently...gentle half throttle pulls up to 4000rpms here and there, driving about about 50-100kms each trip. After 600kms, i did a longer highway drive of 400kms in one go. Car feels amazing and is really responsive, its a totally different beast.

My two questions are...

What oil should you use for break in: I used a 5w30.

What is 'reasonable' amount of oil consumption for the engine break-in period? I added exactly 6.75Ls before the first start since I assumed since the engine was totally dry and it needed a bit more since the oil was now spread out around the engine. But after the first 100km, it asked for 1L of oil which I added. Then after 1000kms it asked for 1L of oil again. I assume this is normal and oil consumption will improve over time. I've heard BMW shipped the new e90s with a 1L bottle of oil in the trunk exactly for this purpose.

If you have had experience with this engine, please comment.

Thanks in advance.

[White94RX]

It should consume less oil once it's broken in. If you've driven 1000 kilometers, I'd start driving it harder. I've always been under the impression that heavy load and high RPM's will seat the piston rings better and reduce oil consumption.

And by the way, BMW never shipped any car with an extra bottle of oil. I've been working exclusively as a BMW dealer tech for 15 years now. I did more PDI's on new E90's than I could ever count. Even the M cars, which notoriously drink oil don't come with a free quart. BMW expects the customer to either do it themselves, or have the dealership add a liter when the light comes on.

Aside from that, I don't recall a single instance, ever, of an E90 needing a quart of oil within the first thousand miles or so.

[ace309]

I have been putting it under load slowing and accelerating on the highways everyday up to 4000rpm, and then after 600kms we did a nice 400km autobahn run in one go with heavy load and high speeds but again, staying below 4500rpms or 160kph. Will add 1L oil and see what happens in another 1000kms.

[Niki39]

I did a rebuild on the same car and engine a year and 9 months ago.

We put elf mineral oil and ren for 1500KM iirc then did a swap to synthetic oil.
It didn't use more than half a liter or 1L for the whole period iirc.
No point using synthetic when you'll swap it out so quickly, and you need a bit of a thicker oil at first as not to overpush it.

Also, I never went past half the throttle. Mixed driving.
Highway should be avoided for break in period as your revs need to vary all the time.
I drove the car mostly between 2000-3000rpm and 1500-2000rpm. Only sometimes 3000-4500, rarely, just to make it used to different engine speeds. But always below half throttle.

Once the break in was past due, flushed the oil with 5w30 and drove for 5000km then another flush with 5w30.
For another 1000km I mostly used light throttle, but occasionally giving the car full throttle and then after that I redlined it a few times next 1000km.
After 15.000km due to oil consumption I tried 5w40 (liqui moly), but oil consumption stayed the same.
All in all, took a little while to get it used to all conditions really. Now the car settled down on using a liter of oil per 2500-4000km (depending on coditions) ever since those first 1500km and stayed the same,

but just few days ago I changed oil separator (CCV) and Disa valve, so it might use 0 oil now, we will see what the future brings.

[jclausen]

For instance my bmw r1100gs when new used oil regularly until I reached 15k then stopped I switched to redline oil at that point. As far as breaking you want to vary engine speed, don’t lug the engine and don’t rev the crap over it, over time you can start to drive it harder

[BuildAndDrive]

I've completed an entire DIY list of videos for the n52 engine rebuild so if you want to rebuild your own engine, you can view them here if you are interested.
https://www.youtube.com/playlist?lis...hSxzbRgM83Yppw