My partners 97 E36 323i has just suddenly died.
She started it today and it turned over normally on the starter but then
suddenly stopped turning, on resetting the ignition key it now turns
over strangely. It is turning the crank but seems slower than normal
and without the normal pulsations (maybe I'm just used to 4 cycls).
I know alot about other 4 cyl cars but the BMW is new ground for me.
It sounds a bit like a cam belt is broken, but the engine isn't spinning
on freely after you disengage the starter, and the manual says the
engine has a chain(s). So I doubt this, could be a simple as a battery?
It has been replaced a few years ago.
Any suggestions would be appreciated.
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
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.
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?
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
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.
Dave Plowman (News) wrote:
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?
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.
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?
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.
http://www.totalseal.com/howdoo.html explains the typical ring
configuration, and implicitly mentions the prevention of the above
problems, while stressing the containment of compression with
the top and second rings.
From : http://auto.howstuffworks.com/engine1.htm
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
Again, similar reasoning. Bottom line: an oil film doesn't (normally)
to compression. If you Google "oil ring piston", you will find these and
other postings that support this.
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'm not being rude. You're just insignificant
Dave Plowman email@example.com London SW
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.
Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here.
All logos and trade names are the property of their respective owners.