Overheating after cooling system refresh – thermostat?
E46 325ci overheating after cooling system refresh
Hey r/e46,
First post here – this is also my first car and my first BMW, so bear with me. Hope someone can point me in the right direction.
The setup: I have a 2001 E46 325ci. I know the fan blade is broken and i am already in the process of replacing it, so let's set that aside for now.
What triggered the refresh: The radiator developed a slow leak, so I figured while I'm in there I'd do it properly.
What I've replaced:
- Upper and lower radiator hoses
- Full radiator (new unit with new plastic bracketing) – replaced due to a slow leak
- Expansion tank and cap
- ATF heat exchanger and all associated components
- Bled the system twice – first with the front of the car lifted nose-up, then again properly with a vacuum filler
The problem: This issue only started after the cooling system refresh – before all of this, the car had no overheating issues whatsoever.
Now, the car starts fine and drives fine for the first ~10km. After that, the temp starts climbing, not into the red, but sitting around 3/4 of the way up and still rising. It gets to the point where I have to pull over and stop driving to avoid overheating.
What I'm seeing in the video: Expansion tank is releasing pressure, and there's a noticeable clunking/ticking sound coming from the area near the thermostat.
My suspicion: The thermostat is the only moving part in that area, and given the clunking sound and the pattern of overheating only after the engine is fully up to temp, I'm thinking it could be stuck or failing – opening late, not opening fully, or just on its way out.
Has anyone seen this exact combination of symptoms on an E46? Is a thermostat replacement the logical next step, or am I missing something?
Any help appreciated.