Knowcking noise in a BMW 525i?

[Russell]

My 1995 bmw 525i with 199,000 miles often has a deep knocking sound on the first start of the day, especially a cool day. Current oil is valvoline max life 20w50 blend with Lubro-moly M0s2 additive.

After it warms up no knocking sound. I have been told it could be “piston slap” caused by wear and most obvious clearances are wide when cold and narrow when engine is warm.

Opinions?

 

[Astro14]

could very easily be piston slap...but the description: "deep knocking sound" is worrisome...ever hear a bad rod bearing?

You need to get someone to hear this sound...could be serious...how long has it been doing this?

 

[Lead Shoes]

The 3.4 GM motor is known for its piston slap on cold start ups so I defiantly know the sound, but a piston slap is a quick clack noise upon cold start up, not a loud knock, id get her checked out by a mechanic asap if its a loud knock...

 

[Russell]

Thanks guys, Actually I have heard this sound for a year or more. No other indications. I can just barely hear it in my garage with the windows closed at idle on first start. I can hear it a little with the windows down and no traffic for the first 1/4 mile or so as I accelerate of idle.

Perhaps a deep knocking sound is the wrong description. Let me listen closer.

 

[Quattro Pete]

Did you try running thinner oil? Does it affect the knocking sound in any way?

 

[Russell]

Originally Posted By: Quattro Pete
Did you try running thinner oil? Does it affect the knocking sound in any way?

Thinner oil such a 0w40 or 5w40 does not seem to make a difference as I remember. Also, I have seen some cool mornings there is no knocking sound. It is a puzzle.

 

[qdeezie]

20w50 might be a little too heavy for your vehicle and might be the reason for the startup rattle. Also, what type of filter are you running?

I know I'm comparing apples to oranges here, but with my truck, there are certain things that I know if I do regarding oil or filter, I will get a startup rattle.

For instance, if I use an oil filter that has a rubber/nitrile ADBV valve, I'm guaranteed to get a startup rattle on pretty much every start if it has has been longer than about 20 mins since I turned off the engine. If I use 10w30 or higher viscosity oil, I will occasionally or consistently get a startup rattle based on the current outdoor temperature. But if I use 5w-30 or 5w-40, no startup rattle to report regardless of the temperature.

If I was you, I'd change the oil to something like a 5w-40 or at least a 10w-40 since it appears you like or need a heavier weight oil and use a filter with a silicone ADBV.

 

[qdeezie]

Just read your comment about 0w-40 or 5w-40. I'd say change your filter to something with a silicone ADBV such as a P1 filter if it's possible.

 

[Russell]

Originally Posted By: qdeezie
20w50 might be a little too heavy for your vehicle and might be the reason for the startup rattle. Also, what type of filter are you running?

I know I'm comparing apples to oranges here, but with my truck, there are certain things that I know if I do regarding oil or filter, I will get a startup rattle.

For instance, if I use an oil filter that has a rubber/nitrile ADBV valve, I'm guaranteed to get a startup rattle on pretty much every start if it has has been longer than about 20 mins since I turned off the engine. If I use 10w30 or higher viscosity oil, I will occasionally or consistently get a startup rattle based on the current outdoor temperature. But if I use 5w-30 or 5w-40, no startup rattle to report regardless of the temperature.

If I was you, I'd change the oil to something like a 5w-40 or at least a 10w-40 since it appears you like or need a heavier weight oil and use a filter with a silicone ADBV.


Thanks.
I believe 20w50 is a recomended oil in this car. It did the start up noise with 10w40 lubro-Moly oil. Older BMWs tend to like heavier oil.

Also the oil filter is a MANN OEM drop in filter on top of the engine. There is no bypass valve built into the filter.

 

[Russell]

Listened to the engine this morning. The sound seem to be coming from top side of the engine. I have told by BMW people that engines with Vanos(variable valve timing) can cause all sorts of noises when worn. From a knocking sound to a "marbles in a can" noise.

 

[antonmnster]

If you're just starting to get VANOs noise at 200,000 miles, you're doing just fine.

I'd actually be a little more suspicious of the timing chain tensioner, the one for the main chain just ahead of the exhaust manifold.

VANOs noise usually announces itself more at higher rpms, and more so when warm. A cold start, chain noise at idle seems to me to be a weak tensioner. They're easy to change and are <$100

 

[Russell]

Originally Posted By: antonmnster
If you're just starting to get VANOs noise at 200,000 miles, you're doing just fine.

I'd actually be a little more suspicious of the timing chain tensioner, the one for the main chain just ahead of the exhaust manifold.

VANOs noise usually announces itself more at higher rpms, and more so when warm. A cold start, chain noise at idle seems to me to be a weak tensioner. They're easy to change and are div>


Thanks. Possible. I replaced the tensioner about 95,000 miles ago. may change it again. Another thought is a loose component like a spark plug. May check them.

 

[Craig in Canada]

EDIT: had a reply about tensioners all written up, but I see you've addressed that. I would take a look at it again.

I second the spark plug comment. I had read about this a number of times but actually had it happen to me once even though I don't run the oft-blamed +4 plugs. It sounded like I developed an exhaust manifold gasket leak.

 

[Russell]

Originally Posted By: Craig in Canada
EDIT: had a reply about tensioners all written up, but I see you've addressed that. I would take a look at it again.

I second the spark plug comment. I had read about this a number of times but actually had it happen to me once even though I don't run the oft-blamed +4 plugs. It sounded like I developed an exhaust manifold gasket leak.


Thanks, An exhaust leak is still the possiblity. I use stock Bosch plugs to avoid the plug type/bland issues so often mentioned. BTW, I recorded the sound on my iPhone. I plan to run it by my mechanic to see what he thinks.

 

[mva]

The noise goes away when warm. Warm oil is much thinner.

20W50 is too thick when cold - try Castrol Syntec 0W30. GC 0W30 is a classic choice for most BMW engines.

If that doesn't get rid of the noise you probably need vanos or other repairs:

http://www.drvanos.com/

 

[Russell]

Originally Posted By: mva
The noise goes away when warm. Warm oil is much thinner.

20W50 is too thick when cold - try Castrol Syntec 0W30. GC 0W30 is a classic choice for most BMW engines.

If that doesn't get rid of the noise you probably need vanos or other repairs:

http://www.drvanos.com/

Disagree with your oil recomendations. My expereince has shown that the engine is very noisy when warm with 0wX oils. One option is a 5w50 oil. i think Castrol makes one. I also liked Lubro-Moly 10w40 with Mos2 which I used it in the winter. may use it again this summer.