Anyone know anything about BMW diesel engines

[Peter Palmer]

I'm having a look at my mates car (2017 X1 118D) which has a bad oil leak. The only place I could see it was leaking from was the oil cap itself, tried a new cap and it made no difference, I then had an air leak issue so did a smoke test, found the leak but it also showed up a crack in the plastic valve cover. I glued that shut and whilst it was off I checked the PCV valve which seemed fine, I put two rubber wahsers on the oil cap and it apperead to stop any more leaks. It drove fine round town for a few days. tonight though we gave it a run on the motorway and when we got back there was smoke coming from the back of the engine where the exhaust is, obviously burning oil.

Now there is smoke coming out of the dipstick tube when you pull it out, but the exhaust is sparkling clean, I'm thinking blow by gasses pressurising the oil up and forcing it out of gaskets but you would have thought that it would start leaking out of the original places if anywhere.

But my other thought was whilst I was messing around with the code reader I re-set the DPF back to a "new" one as the pressure looked alright and it was saying "near end of life" in the code reader but I think they are pre programmed to say that automatically whether its good or bad. So maybe this was the first chance its had to do a re-gen in ages and it was just burning excess oil off the exhaust, it really was caked in oil when I was trying to clean everything off the other day.

Any thoughts?

[mickthemaverick]

I think you'll have a much better chance of help at:

https://www.bimmerfest.com/forums/bmw-d ... iasts.154/

[CitroJim]

Now there is smoke coming out of the dipstick tube when you pull it out, but the exhaust is sparkling clean, I'm thinking blow by gasses pressurising the oil up and forcing it out of gaskets but you would have thought that it would start leaking out of the original places if anywhere.

Sounds like excess crankcase compression caused by worn bores and/or gummed/worn piston rings at first thought.

Is the oil level dropping noticeably or is it rising? Also, sniff the oil and see if it smells a bit 'diesel-y'. often excess bore wear or failed rings will cause some liquid diesel to find its way into the sump and raise (and dilute) the oil. If the oil rises too high the engine may start running on its own oil and this might end in a very bad way.

The exhaust will likely look clean as the DPF may well be doing a lot to consume the smoke and particulate resulting from the oil burning.

This will very soon destroy the DPF.

A diesel leak-down test (a compression test in reverse) will confirm if the problem is with worn bores or failed piston rings.

[Peter Palmer]

Thanks for the replies, I've seen a leak down test mentioned before, but is this not where you connect bottles up to the injectors and see how much diesel is being leaked back, what is a leak down test on the cylinders. I do think it may be high crank case pressure but when its cold or just run round town it seems absolutely fine, it was only when it had a good run yesterday that it spat its dummy. It did seem remarkably hot under the bonnet though when we opened it, I know its a long shot but I'm just hoping it was a re-gen burning off old oil. Apparently my mate is driving it to Birmingham today, a journey of 80 miles or so, so either it will be fine or I'll have to put my AA hat on and go and rescue him. I think we will have a result either way by this evening.

[mickthemaverick]

Picking up on Jim's thoughts, does the engine have a PCV valve fitted (Positive Crankcase Ventilation Valve) and if so it may be jammed shut? Just a thought.

[bobins]

A leak down test in this respect would involve removing each injector and screwing in an airline into each injector port in turn, then make sure the valves are closed on that cylinder and then apply air pressure. You're looking to maintain a pressure (within reason), but also you can listen for air leaks - via the inlet manifold, exhaust manifold, or crankcase (oil filler). An automotive stethoscope is handy for this.

[Peter Palmer]

Picking up on Jim's thoughts, does the engine have a PCV valve fitted (Positive Crankcase Ventilation Valve) and if so it may be jammed shut? Just a thought.

PCV valve is fine, I took it to bits to check and it doesn't hinder the smoke test in any way. The PCV valve is a bit strange on them anyway, its build into the valve cover and a spring holds a diaphragm open so the PCV valve is normally open, it only shuts when the turbo spools up and drags the valve closed supposedly.

[Peter Palmer]

A leak down test in this respect would involve removing each injector and screwing in an airline into each injector port in turn, then make sure the valves are closed on that cylinder and then apply air pressure. You're looking to maintain a pressure (within reason), but also you can listen for air leaks - via the inlet manifold, exhaust manifold, or crankcase (oil filler). An automotive stethoscope is handy for this.

Cheers, is this a better way than just doing a compression test?

[mickthemaverick]

You may find this helpful Peter (Not that I have a vested interest or anything! ) https://www.ebay.co.uk/itm/326710080067

[bobins]

Cheers, is this a better way than just doing a compression test?

They both have their merits. A compression test is relatively easier to perform. A compression test will confirm if there is a problem, whereas the leak down test will point to where the problem is. If either of them indicate a problem..... it points towards a ballache

[xantia_v6]

Does that engine have a second PCV valve that opens to the turbo inlet when the engine is on boost?

[Peter Palmer]

I don't think so, the only place the crankcase is open to the inlet is the PCV valve on the back of the valve cover from what I can see.



Its that round disc under the number 13, it goes straight to the air intake pipe right before the turbo.

[CitroJim]

You may find this helpful Peter (Not that I have a vested interest or anything! ) https://www.ebay.co.uk/itm/326710080067

That will do the job nicely and likely cheaper than a full leakdown test...

[Peter Palmer]

Its now been on a 200 mile round trip and my mate reckons its fine, no burning oil smells and it drives fine apparently. Not sure what was going on then.