Hi all
I have a newly acquired Mini R56 that's burning oil (smoking tail pipe, need to top up oil).
A cylinder leak down test shows minimal leak (under 10%), but spark plugs and top of the pistons are wet with oil.
Where else do these engines leak oil?

Engine is N12 with 42.000 miles.
Tips and ideas appreciated. Thank you.


All 4 spark plugs have varying degrees of oil


outside of spark plug well is clean - no external leak


Leak down test done at 30 PSI

 

Valve stem seals are common failures but oil burning is usually rings, especially on the R56. What are the compression test numbers?

 

Given the good leak down numbers I would suspect an issue with the crankcase vapor recovery system. This is designed to recover oil vapor from the crankcase gases, if it goes bad it'll dump a bunch of oil into the cylinders.

I'm not an expert on the N12 but I believe from discussions that this was a fairly problematic part. I think the system is incorporated into the valve cover and there's a rubber membrane that can tear. Try doing a search.

 

oldbrokenwind: compression numbers were good. All four cylinders were around 15 bar (217 PSI)

Gubi: I did read that in a thread, but am not sure how to test it. I disconnected the hose at the passenger side of the valve cover and there is some oil seeping into it (should there only be vapor?) .. and the valve cover is pricey, oh my!

Can the vapor alone make the car blow smoke continuously when hot?

 

Smoke would be a symptom, yes, but I don't know how to test the Mini's separator. A shop may have the tools to measure crankcase vacuum and know what the spec is.

 

It looks like ECS has the part for $153. That's honestly not bad.

https://www.ecstuning.com/b-uro-part...127646554~uro/

They also have just the membrane for $32, so it's likely possible that you can just swap that out if it's failed.

https://www.ecstuning.com/b-vaico-pa...127646554~vai/

 

Tips are dry and burn looks eh ok. But wet top of plug means valve cover gasket and O rings need replacing....Oil is making its way into the tunnels for the plugs via valve cover gasket rings...

R56 always smoke some if at start up...The tollerances for pistons runs wide....why you can only put so much HP into those prince engines due to piston slap.

gasket kit

 

+1. Valve cover. Will cause the leaks you see and oil burning. I have had both corrected with new a valve cover. It may not be the only reason you are burning oil but with good compression and leak down numbers I bet it is a big part of it.

 

@Eurothrasher: Correct, the tips are dry. But shouldn't the spark plug well show sign of leakage above the plugs, if we were to suspect the gasket.

I wonder if the result would have been different had I done the leak down test at a higher pressure, say 100 PSI, instead of the 30 PSI that I had at the shop.

 

Replace Valve Cover with PCV and Gasket. Start simple.

 

I've ordered an inexpensive vacuum gauge (manometer) to measure the vacuum in the crankcase before I proceed.

For future reference these are the pressure/vacuum specifications for the different engines:
N12 : 22 mBar
N14 : 38 mBar
N16 : 36 mBar
N18 : 36 mBar

Crankcase pressure diagnostics:
https://www.import-car.com/tech-tip-...ment-pressure/

HOWTO video:

 

Finally got the vacuum/pressure gauge delivered - took some time.

It's measuring between 41 and 45 millibar of vacuum, which is excessive.
Spec for my engine is 22 millibar. Oh well, time for new valve cover, I suppose :(

 

Pretty common issue, and fortunately one of the less serious causes of oil consumption.

Valve cover looks to be pretty reasonably priced, but you may be able to just replace the membrane since they sell the part separately. Dunno how challenging that is, perhaps do a search.

 

so what is end result ?? Did you change the valve cover ? Or just membrane?

 

I replaced the valve cover. The car is still burning oil (smoking).
I suspect valve stem seals or piston rings at this point.

 

Burning oil out the tailpipe? With good compression I bet it is the guide seals. Been there and done that too. Make sure you get the ones for the N14 not the W11 engine. Some suppliers don't know the difference (stem and base diameter of the N14's are smaller than the W11's). I know because I have two extra sets of W11 stem seals.