2002 3301i E46 Coolant Leak

[windtunnel]

I have a coolant leak and it does not show up any where on the driveway. It leaks about a quart out about every 750miles. Any suggestions?

[MarcoZandrini]

That’s a lot of coolant being lost over a very short distance. Is the exhaust whitish? Does the exhaust smell sweet? How does the car run?

[jclausen]

Did the engine over heat recently ? If it was a high mileage car and there were no white spray patterns in the engine bay, I would look closely at the plastic coolant pipes under the intake manifold where they connect to the block behind the oil filter stand. But a coolant pressure test by a shop will find it

[legoman67]

these cars have undertrays that would catch drips. It may only leak when its hot (the system is under much higher pressure when the car is at operating temperature). The best way to find it is to have the system pressure tested. You could also look for traces of coolant at the front of the engine. Coolant will leave very white water stain marks on the black plastic in the engine bay.

[curry]

I may be wrong here as I am relatively new to e46's, but With e36's with a M50 there is a hose that enters the block under the intake manifold. If they are old they will leak at the connection to the engine and the heat of the engine will lead to little or no puddles. They seem to leak the most while driving and the revs are up. This may be a place to look for your leak if there is such a hose on an M54. I think it's likely there is.

[Jackson42]

There are two plastic coolant pipes - one from the side of the head, and one from behind the water pump - that crumble with age. When they start to leak, it's difficult to isolate because they are behind or under the intake manifold. With the age of your car, and not knowing the mileage, I'd suggest that one or both of them are the culprits.

[charter21p5]

^ this

use a coolant pressure tests to find the source. Those plastic hoses he is referring to are good for ~180k miles.