Removing over-tightened coolant reservoir cap
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Joined: Mar 2020
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2012 E350
Removing over-tightened coolant reservoir cap
We got a new-to-us 2019 E300 with 83k miles in November.
Went to check the coolant today and it seems like the last person to replace the coolant cap over-tightened it past the detent bump, and the cap is stuck on.
What is the proper way to remove this cap without damaging the plastic reservoir bottle? I don’t want to introduce any hairline cracks (or worse) by prying.
Went to check the coolant today and it seems like the last person to replace the coolant cap over-tightened it past the detent bump, and the cap is stuck on.
What is the proper way to remove this cap without damaging the plastic reservoir bottle? I don’t want to introduce any hairline cracks (or worse) by prying.
Super Member
Joined: Dec 2015
Posts: 599
Likes: 237
From: Suburban Maryland
2023 E 450 Sedan. 2018 GLC 300. 2013 E 350 Coupe (retired)
Could you destroy the threaded area of the cap with a sharp blade, or just cut the tabs, and remove the cap? If so, replace with new cap.
Last edited by smiles201; Mar 2, 2026 at 11:00 PM.
Super Member
Joined: Aug 2019
Posts: 594
Likes: 171
From: USA to Germany
W221/W222/W213/X290
We got a new-to-us 2019 E300 with 83k miles in November.
Went to check the coolant today and it seems like the last person to replace the coolant cap over-tightened it past the detent bump, and the cap is stuck on.
What is the proper way to remove this cap without damaging the plastic reservoir bottle? I don’t want to introduce any hairline cracks (or worse) by prying.
Went to check the coolant today and it seems like the last person to replace the coolant cap over-tightened it past the detent bump, and the cap is stuck on.
What is the proper way to remove this cap without damaging the plastic reservoir bottle? I don’t want to introduce any hairline cracks (or worse) by prying.
In all honesty just go ahead and twist the cap off while the engine is cold. Do not try to warm it up, as the pressure from the warm coolant will make it harder to remove, and possibly dangerous as well
I'd buy a new cap directly from Mercedes and install it. Drive it around and get the car up to temp. Monitor the new cap and coolant reservoir for leaks and any dashboard lights that come on. Monitor the coolant temp and level for a while as well.
If you have any issues, replace the reservoir. That's what I did in the end.
