Fuel pump locking ring
Thread Starter
Newbie
Joined: Jan 2026
Posts: 10
Likes: 0
ML W164 M273
Fuel pump locking ring
Hi guys! One of my fuel pumps is leaking and there is a gasoline smell in the car. I've narrowed it down to the right-side fuel pump leaking. I removed the locking ring to check the o ring, but that's fine - no cracks, it's supple and looks good. However, now I can't tighten the locking ring fully (which I assume is the issue in the first place as someone has obviously worked there previously). After a certain point it just won't budge any more. The thread on the fuel tank is apparently removable and has a gap which should, I assume, compress when I tighten the cap, but instead it splits even more and I guess that's the reason for the issue.
https://prnt.sc/Mi_7uCxlwo8Z
I've highlighted the bit I mean.
Any tips from someone who has done this? Do I need to compress it with something like a zip tie and then tighten? Or maybe there is a special too? Or this park should be changed fully after one use?
Thanks a bunch in advance!
https://prnt.sc/Mi_7uCxlwo8Z
I've highlighted the bit I mean.
Any tips from someone who has done this? Do I need to compress it with something like a zip tie and then tighten? Or maybe there is a special too? Or this park should be changed fully after one use?
Thanks a bunch in advance!
Super Member
Joined: Oct 2023
Posts: 606
Likes: 208
W221 S500
Hi guys! One of my fuel pumps is leaking and there is a gasoline smell in the car. I've narrowed it down to the right-side fuel pump leaking. I removed the locking ring to check the o ring, but that's fine - no cracks, it's supple and looks good. However, now I can't tighten the locking ring fully (which I assume is the issue in the first place as someone has obviously worked there previously). After a certain point it just won't budge any more. The thread on the fuel tank is apparently removable and has a gap which should, I assume, compress when I tighten the cap, but instead it splits even more and I guess that's the reason for the issue.
https://prnt.sc/Mi_7uCxlwo8Z
I've highlighted the bit I mean.
Any tips from someone who has done this? Do I need to compress it with something like a zip tie and then tighten? Or maybe there is a special too? Or this park should be changed fully after one use?
Thanks a bunch in advance!
https://prnt.sc/Mi_7uCxlwo8Z
I've highlighted the bit I mean.
Any tips from someone who has done this? Do I need to compress it with something like a zip tie and then tighten? Or maybe there is a special too? Or this park should be changed fully after one use?
Thanks a bunch in advance!
That it's not sitting right, you have fumes already AND someone has been there before... I would strongly advise replacement.
Thread Starter
Newbie
Joined: Jan 2026
Posts: 10
Likes: 0
ML W164 M273
Noted! So with the replacement it should be much easier to actually tighten the lock ring and it's not just me being a dummy?
Super Member
Joined: Oct 2023
Posts: 606
Likes: 208
W221 S500
WIS strongly advised against this and in your case, being petrol and the fact you can't get the lock rings to seat correctly, new parts would be my starting point.
Thread Starter
Newbie
Joined: Jan 2026
Posts: 10
Likes: 0
ML W164 M273
I had to open up both sides of the tank on my diesel to trouble shoot a failed fuel gauge. I don't recall having any issues once I bought the correct tool for the locking ring. And I will be honest, I reused everything.
WIS strongly advised against this and in your case, being petrol and the fact you can't get the lock rings to seat correctly, new parts would be my starting point.
WIS strongly advised against this and in your case, being petrol and the fact you can't get the lock rings to seat correctly, new parts would be my starting point.
I assume gasoline and plastic don't really yield to easy tightening. I have the tool, but I fall short about 1/4th turn until it's between min and max (I line up everything as per the procedure). If I try to tighten it more it's incredibly difficult and I end up breaking the ridges on the cap. I'll see how it goes with the new part and ask if I have any questions
