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Go Back   Bimmerfest - BMW Forums > BMW Model Discussions > 3 Series / 4 Series > E36 (1991 - 1999)

E36 (1991 - 1999)
The E36 chassis 3-Series BMW was a huge hit among driving enthusiasts from the first moment the car hit the pavement. The E36 won numerous awards over the years it was produced and is still a favorite of many BMW enthusiasts to this day! -- View the E36 Wiki

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  #1  
Old 08-22-2006, 11:48 AM
c0ximo c0ximo is offline
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328i engine knocking sound

hey guys, first thread here...i hope this hasn't been answered. but anyways, i've had this problem with my 1996 328i for a year or so now. it hasn't been properly diagnosed or fixed by numerous mechanics. everything with my car sounds fine until it warms up to full operating temperature. then a knocking noise from the engine sounds in 5 second bursts followed by a loud metallic thud. it happens continually and is especially noticeable when stopped at a light. i always put in 93 octane in the car and have no mods. performance seems as good as always. one mechanic said it could be a bum valve but i'm not sure. does anyone else have a similar problem to this?
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  #2  
Old 08-22-2006, 03:54 PM
AW328i AW328i is offline
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Have you noticed any kind of power loss, or anything else that you think is attributable to this knocking sound? If it's happening on a cyclical rate every five seconds or so, then it's most likely some component of your engine. Maybe your water pump since it only makes the noise when it's warmed up?
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Old 08-22-2006, 11:12 PM
c0ximo c0ximo is offline
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i haven't noticed any significant power loss. but one hint that may help: my son took the car out on a cold new england day and red lined it soon after starting it. with such a cold start, what components could be damaged?
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Old 08-23-2006, 01:16 AM
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Pirate_copy Pirate_copy is offline
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Mein Auto: M3
I have this too.

it is something to do with the heater valve. as you look at the engine, it is at the very back, slightly to one side (right on my 328i) and looks like a camera film canister bolted to the bulkhead.

When it starts happening, pop the hood and listen for the noise at the very back of the engine. Mine does it when i turn the ignition on some times

My mecanic said it happens quite a bit but is not doing any real harm. said to just replace it when i can be bothered.

If it isn't that, it definitly sounds like some kind of valve sticking.

As for red-lining it from cold, this causes a problem with the piston rings and pistons. As i understand it, the pistons are made of a metal that heats quicker than the block and rings and so when you rev the car hard when it is cold, the piston expands quicker that the block (cos of the heat) and so scoring occurs on the piston ring. This however would not really cause a knocking, but rather power loss as you would lose compression. Another problem is that the oil might not have circulated around the engine and so metal components would be rubbing together as opposed to having an oil buffer between them, this would cause a constant or intermitant noise and not one that is in 5 second cycles (often a tapping from the Hydraulic valves at the top of the engine that changes speed and tone as the revs go up and down).

Although we have all done it, it is always better to warm up a car before giving it some wellie.....not that that is always possible

Check your valves is my advice mate

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Last edited by Pirate_copy; 08-23-2006 at 01:26 AM. Reason: added stuff
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Old 08-23-2006, 09:16 PM
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Rickman Rickman is offline
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I also read somewhere that you can damage the main bearings from over revving an engine when cold. It said that they are underlubricated and cook, then stick on the crank. Probably not the best description but it is real important to warm up the engine first. The article was referring to an M3 engine in an E46, but I guess the same principles apply. My 323 engine is a Nikasil bore, so I'm extra careful in warming it up properly to avoid damage.
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