Today I noticed the engine temp rising a bit. [Solved]

[oldskewel]

Originally Posted by titodj

... i noticed leak stains on the expansion tank, so the tank obviously failed ...

Until you see the crack, and see the coolant leaking out of it, I would not assume the tank has failed yet.

If there is an overpressure condition, the cap on the expansion tank will vent coolant, allowing it to flow onto the tank, etc.

If your engine overheats, you might warp the head or damage the head gasket. That would allow combustion gases to enter the coolant, raising pressure beyond the 2-bar cap release setting, allowing coolant to exit through the underside of the cap.

And I know all this because I went through it all on my 2001 3.0i earlier this summer. In my case it was a slightly warped head.

Here's a post on how you can pressure test your cooling system, if you can rig this thing up:
https://xoutpost.com/bmw-sav-forums/...ystem-e53.html

For me, doing that test ruled out any cooling system leaks, so I moved onto the next test, which was a Lisle combustion gas detector, giving me the bad news.

If all of this testing is beyond your limit of tools availability, you could try this as a test:
Clean and hose everything off around the expansion tank. Roll up a paper towel and wrap it around, under the expansion tank cap. That is where the pressure-released coolant comes out - between those ribs on the bottom of the cap. Then run the engine / drive around until it leaks. If you see leaks below, and on the expansion tank, but the paper towel is dry, then it is not the expansion tank releasing. If the paper towel has coolant on it, it could be what I'm suggesting above, or it could be a failing cap (o-rings, etc.) that is leaking even though the coolant is not over-pressurized.

[titodj]

Originally Posted by oldskewel

For me, doing that test ruled out any cooling system leaks, so I moved onto the next test, which was a Lisle combustion gas detector, giving me the bad news.

Thank you, I don't see any liquid stains close to the cap, but I guess is possible that the tank is not leaking, I saw your post on how to test the system pressure (genius), but I don't have the bleader or a spare cap.

But I will definitely get a combustion gas detector kit to make sure is not the head gasket and ruin the engine while focusing on the cooling system.