E36 spinning on starter

I think now that the cranking speed is normal but it just sounds like there is no or reduced compression. Seems like some sort of mechanical breakage.

There is alot of unusual knocking from the dashboard(engine?) after you switch off the ignition after a start attempt.

There is plenty of power in the battery/starter, it can jump the car forward if left in gear during a start.

-- T> My partners 97 E36 323i has just suddenly died.

Ok I've tried it again and it seems to be sounding more like it has compression now, more like no fuel or spark.

Where do you start with this engine, all my normal test techniques can't be easily done, like looking for spark.

What can happen that does not cause the engine check light to come on?

T> I think now that the cranking speed is normal but it just sounds like

Try flooring the throttle and cranking - release immediately it starts. If they don't start immediately the system can get confused.

I don't know why you didn't explain this, I'd much rather learn than be told what to do. I had already tried that (my standard flooding fix, but not really necessary with modern injections), so I didn't really pay it any attention until I had thrown in the towel and called a local specialist to take it away. Without charging a penny he said that these cars need oil on the piston rings otherwise they lose compression almost completely, and sometimes on a cold start there is too much petrol and it washes off the oil. So I had detected compression loss correctly, I just didn't think it was possible for not to be a mechanical/broken part fault.

I had the previous night driven the car for less than a minute when cold (moving it in the drive way) and then left it overnight. I guess this left excess fuel in the bores which removed some of the oil, the remainer of which was washed away on the early morning cold start (its about 3-4C during the long nights here now).

Anyway his suggestion was similar, but he did say it needed ages to catch and if it didn't work, take out the plugs and pour in some oil, or tow it (not a good idea for a catalyst car). I topped up the oil and used up the battery but on sticking in a replacement from the other car I got it to catch within a few minutes. I had to really abuse the starter, but it sounded fine, I hope I don't have to pay for that later. The car is now working normally again.

The car is in general excellent condition and quite well looked after, I do use Mobile 1 in it, but the cooling thermostat needs replacing (stuck partially open I think) and I wonder is that combination likely to make the problem worse. I does get a good run each day and gets upto the proper temp despite that. (I tried to replace it a few months ago and only had time to figure out how to get the fan off).

I hope someone finds this useful.

-- T> >> Ok I've tried it again and it seems to be sounding more like it has

Ah - if only you had said this. It's pretty standard that they misbehave if you do this.

I don't think it's anything to do with compression. It's just the engine management getting all confused.

Agree - it's a very nice story that the mechanic told - but it's basically bullshit. The rings don't depend on an oil film on the cylinder wall to seal..

Don't do that - if you start it - let it run for at least 2-3 minutes before shutting it down. If not - learn to do the pedal to the floor crank until it starts routine. On early Motronic systems - stopping the cranking and starting it again will result in further flooding since the cold-start injector is triggered each time with the starter. Later models don't have a cold-start injector, the Motronic performs the richening function using the standard injectors.

No, I really think the compression was lost and that is why it won't start. You can hear the engine just turning without any oscillation. , just more of a whirr. My initial impression was something seriously mechanical like a broken cam belt, I've been working on cars for 20 years, I know what no compression sounds like and I'm an Engineer, it makes perfect sense, I too didn't believe it was possible in a modern car, but hearing how the starting note changed convinced me.

How sure are you the compression doesn't depend on the oil?

-- Tony

It's much more likely that the vanos solenoid or hydraulic piston was stuck that caused the valves to remain open/overlapped and caused the compression loss.

It doesn't. The mechanic was talking about the fact that, if the rings are worn *badly*, adding oil to the cylinder will momentarily help them seal and allow you to diagnose worn rings. But we're talking about several ounces (1/8 cup?) to do this.

FloydR

I thought about the Vanos system, but surely it doesn't have that much range? Why would running the starter over and over get it started eventually? The starter revs will easily build enough oil pressure. It doesn't just suddenly get better its very gradual.

Why would only happen if you run the engine for a minute when cold? Apparently this happens alot with that cause.

I don't agree, liquids really help sealing. I know mechanics aren't the most qualified of people in general and will tell their favouite theory even if it doesn't stack up, but I'm still not convinced he was wrong.

So if adding oil (small amount) down the plug holes where to fix this particular symptom/cause would you believe it then?

-- Tony

If you're used to only a four cylinder it could well be the BMW 6 turns over on the starter rather like there's no individual compressions. Only way to prove this to yourself would be to try another one.

I am comparing it to when it is working, not to a 4 cyl, it did have me confused initially. I got it going again BTW. Sometimes when it is faulty and you are cranking it starts to puff a little (increased compression) after this it starts to run a bit and if you can make about

2000rpm it will then start, sometimes it just whirrs in a constant way (reduced compression). After a good run the starting sound normal (ie with compression IMO).

I think the only way to prove it would be to make it go faulty again and then use a compression tester. But now I know how to avoid it, I'm not going to make work for myself.

-- Tony

If oil was used for the seal between the piston and cylinder, oil would be introduced into the combustion chamber, *AND* burned fuel/air would be introduced into the crankcase. The former is what happens to old/worn engines and increases pollution and reduces power. The latter causes contamination of the oil and leads to lubrication failure.

explains the typical ringconfiguration, and implicitly mentions the prevention of the aboveproblems, while stressing the containment of compression withthe top and second rings. From : Piston rings Piston rings provide a sliding seal between the outer edge of the piston and the inner edge of the cylinder. The rings serve two purposes: a.. They prevent the fuel/air mixture and exhaust in the combustion chamber from leaking into the sump during compression and combustion. b.. They keep oil in the sump from leaking into the combustion area, where it would be burned and lost. Most cars that "burn oil" and have to have a quart added every 1,000 miles are burning it because the engine is old and the rings no longer seal things properly.

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Again, similar reasoning. Bottom line: an oil film doesn't (normally) contribute to compression. If you Google "oil ring piston", you will find these and other postings that support this.

FloydR