Spark plug ceramic nose cracked.M43 BMW engine.?

Question

Spark plug in No 4 cylinder on my BMW 3 series M43 engine is regularly cracking its ceramic nose. (3 plugs in 9 months)
My local dealer has said this due to a blown head gasket, at £900 pounds to replace.
I am slightly baffled, as the engine is not loosing coolant and the car runs fine until the plug breaks down. and would value any other ideas.

Answer 1

The only thing that I know of that cracks the ceramic on spark plugs is severe heat, if that is the case the #4 plug should literally be ashen white in color in comparison to the others.
But at three plugs in 9 months the plug doesn't even have much of a chance to get to a good readable point on a modern engine.
I would have them try to explain this head gasket phenomenon,
but I still stick with the inclination that this one cylinder is running hot for some reason.
Install a one heat range lower plug in that cylinder only and see what happens.

Answer 2

check the valve clearances are correct them perform a compression test (if pressure is low on no 4 (this could indicate a valve burning out) if not conduct a cylinder leakage test (the cylinder is presurised with an airline) and listen (making sure that the values on no 4 are closed) with a piece of rubber tube at strategic points to locate any loss of compressed air from no 4 cylinder ie at inlet and exhaust ports dipstick hole oil return way in cylinder head.
if air can be heard leaking when listening through no3 spark plug hole then the gasket is ruptured or burnt through between these two cylinders, excess heat or a very weak mixture are the two most likely causes of this cylinder overheating and damaging the spark plug if these tests produce a negative result try squirting oil round the manifold gasket of no4 where the manifold joins the head if the revs pick up you have established a weak mixture on this cylinder

Answer 3

The head gasket can leak out to the side missing any oil or waterways. If it is it will be pulling extra air in on the induction stroke which will make the cylinder run lean. When it runs lean the combustion temperature rises considerably thus causing an overheating and cracking spark plug.

Answer 4

I'd be inclined to speak to another dealer.

While it's possible for the head gasket to go in such a way that it doesn't affect the coolant or oil, I'd expect the engine to be running less than smoothly.

Answer 5

Buy a different make of spark plug
Try to obtain a set of plugs of higher temperature as some work much better at high temperatures than others

Answer 6

Never heard of that b4, could be the mechanic cracked the plug on fitting, easily done.

Ps the plug at fault , it wouldnt happen to be an awkward one to get at to remove and refit, again this is why I think that it was the mechanic who broke it and not owni ng up, after all plugs are cheap.