[nik patel]

Hi

Currently the car has done 86,500 and suffers a little blue smoke now and then on start up and burns about half a litre every 1,000 miles.

Currently using 5/30 fully synthetic oil, due to the mileage should I use slightly thicker oil now? Which spec do you recommend?

[DriverLDN]

Hey Nik,

What model is your E90?

My E90 330i is at around 77k miles and I'm using the stock recommend 5w/30 which I think is very common.

Bhavik

[nik patel]

Hi, its 325 M sport.

I am just thinking maybe its time to switch to a thicker oil? and maybe it will help with the blue smoke?

[DriverLDN]

I think there could be more to it than change to thicker oil. There could be a few things that could be causing the issue such as a potential gasket issue, injector etc.

I'm no expert though, I'm sure someone will come back to you.

[old grey steve]

Nik nothing wrong with the oil you're using we use 5w30 and have done without issues for years but if you are seeing visible/noticeable smoke that's blue in colour, to me first port of call and a fair bet to place odds on is the possibility that you may have a commonish issue re your breather system, depending on what model you have (N52 or N52N/N53)will depend on whether you are replacing the breather system(the earlier N52 will have the crankcase vent system with the breather and 2 vent and 1 return pipe, while the later spec N52N was amended with its single vent hose assembly and cover, the later N53 version is fully encased with its integral breather/rocker cover assembly) whst you'll need to look at replace will depend on what engine you have.

One simple thing you can do perhaps is to while the engine is ticking over is to simply remove the oil filler cap (check the cap for condensation signs) and see what happens if you detect a drop in revs, a fluctuation in revs or most probably the sensation that the cap is being sucked back in situ then it's fair to say that the breathers compromised and its sadly in higher mileage units fairly common. If the car has/had a dip stick you can also see if the revs drop/car stalls by lifting this while again the cars ticking over. Watch this video for an idea re what you may well find while removing the oil filler cap(sadly American but you get the idea)

These cars do however use a little oil it's fairly common that a little is used through normal everyday running. If you at seeing blue smoke as aposed to condensation from the exhaust the conformation that the car may have a compromised breather would be my first point of call.

But back to a possible breather issue basically if you have the earlier system with the N52 engine the pipes are known to block, collapse and clogged up plus of course the actual valve diaphram can collapse its common and this will cause the blue smoke effects you are seeing, the smoke I'm guessing may be more visible when pulling away and when blipping the throttle for instance say after leaving the car ticking over for a small period of time if its fairly bad you can also get a small amount of pick up hesitation too.

[nik patel]

Hi Steve, thanks for the info. So if it's the breather the hissing noise should occur with the oil filler cap?

A couple of mechanics had a look and they don't think it's the breather. They say it might be the oil stem valve seals?

[old grey steve]

Originally Posted by nik patel

Hi Steve, thanks for the info. So if it's the breather the hissing noise should occur with the oil filler cap?

A couple of mechanics had a look and they don't think it's the breather. They say it might be the oil stem valve seals?

That was another option, much like possible piston wear but its rare on these to see stem seals and not unknown to hear of possible ring wear but if it is the case that he stem seals are an issue its a b******d of a job in terms of time and of course wallet impact, the rings would need to be approached carefully (a compresion test would help plus ascope in the bores with a camera) for signs of borewash, but on the breather side seen the breather system misdiagnosed a good few times on these but like all things worth doing the basics, but if it proves to be an issue re the stem seals seen some goodish results on 645i's with a oil fortifer added We use on the odd occassion this http://www.forteuk.co.uk/product-det.../Oil-Fortifier.

The hissing you heard on the video clip is a bit extreme the ones we see don't usually show those extreme signs but usually you get the sucking effect re the oil cap as demonstrated.

But as you know Nik damn difficult to diagnose anything from word of mouth nad a keyboard but you know where I am if you want to get it booked in

[nik patel]

Thanks again Steve. I tried the forte last August and didn't notice any difference but did see the oil filler cap was cleaner.

[abeardo83]

Half a litre per 100miles is alright for an n52. I had a e89 Z4 that would use around 1l per 1000miles (that was a 2.5l N52). BMW said it was normal?! Funny considering my N54 uses about 1l every 4000miles (and i'm pretty sure that I've got an oil leak somewhere on that!)

I'm with Steve - i reckon it's a blocked breather that's causing the issue. 85k isn't a huge number of miles in respect to wear. Too many people are still attached to this "OMG 100k miles... my engine's on it's last legs" train of thought.