Bottom of engine knocking NEED HELP!!!

[Bleier325]

When the car is idling i am hearing knocking noise from the bottom of the engine and i can't figure out what it is.: I dont want to drive the car until i figure out what it is so if you could let me know what you think that would be great because i stuck not knowing what to do. Also I dont know if its relevant, but i have coolant leak that is comming from passengers side of the car up front by the rad. and coolant tank, im trying to track that down now also.

[4evrwyntr]

The leak is probably from the expansion tank/thermostat housing. That area (where it connects to the radiator by hose) is a typical area leak. If it isn't leaking where the thermostat goes in, you might be able to tighten the hoseclamp (follow the expansion tank down, if the last person who touched your radiator was nice, the hoseclamp screw will be visible. Get a long flathead).
What's the knocking noise sound like (I know, redundant question)? Is it more of a metallic rattle? From the bottom of the front then, not under the car like exhaust?
I suspect it could be several things - most are bad. It might be tied to your radiator leak, and you might have a failed water pump... or the bearings are shot...

[Delmarco]

Engine knock is usually and most commonly caused by using lower than rated octane for your car. Remember for BMW e36/3 series use only 89 octane or higher. Do not use 87 octane?

[Bleier325]

I only use 91 octane or above, thats all i have used since i got the car. Is there any mechanical problems that can be associated with knocking on the bottom end of the car i think closer to the drivers side and it is only noticable when the car is idling. Any input is great! Thanks

[dirtybeemer]

It is hard to diagnose like this it really could be anything whats the oil level like in your car the reason i ask is that it could a big end shell bearing or it might be the water pump ratteling it really could be anything the best thing to do is take it to a garage

[walshja]

could be your VANOS, mine make a lot of noise . . .

[4evrwyntr]

But that's more of a rattle as well... Maybe it is something with the oil... whatever it is, knocking is worse than rattling, probably.