Help with w205 chirp/squeak/grinding
Bought my first 2017 W205 C300 last year at 126k miles from a shady dealer (bad decision, I know), but thankfully I bought a warranty with it.
Since day one it had a chirp/squeak coming from the belt/pulley area. It always got worse with the A/C on. Around 131k I replaced the serpentine belt, tensioner, and idler pulley with an FCP Euro kit. The noise went away for a couple days, then came back. Weirdly, once the weather got cold the noise mostly disappeared.
Then a completely separate issue started — the car began shaking badly, smelled like gas, and started misfiring on all cylinders. I took it to a reputable Euro shop and after a leak-down test they found bent valves and loss of compression. They originally recommended a full engine replacement, but my warranty only approved a head rebuild. I paid about $600 out of pocket.
After rebuilding the heads, the car still misfired during testing, so they rechecked everything and eventually got the warranty to approve replacing the bottom end too. They ended up installing a 64k-mile long block. Warranty covered almost $13k total thankfully.
After getting the car back it ran great, but the chirp/squeak returned. Again, worse with the A/C on. I also noticed red rust around the alternator and started wondering if the alternator or A/C compressor was failing.
I took it back to the shop:
- A/C pressures checked okay (around 40 low / 160 high)
- They said everything tested fine
- They didn’t hear anything concerning
I kept driving it, but now within the last few days the noise has gotten worse. I’m hearing more of a metallic grinding/chirping sound.
My friend who’s a mechanic removed the belt and spun all the pulleys by hand. Everything felt smooth, but while the engine was running he thought the crankshaft pulley might have a slight wobble. Hard to tell for sure.
Other notes:
- Motor mounts definitely need replacing
- There’s also what sounds like a loose rocker arm or solenoid tick coming from one cylinder
- Alternator spins quietly by hand despite the rust around it
Has anyone dealt with this on a W205? Could a crankshaft pulley/harmonic balancer make noise mainly under A/C load even if the pulleys feel smooth by hand? Trying to narrow this down before I start throwing parts at it again.