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Can you tell me about rear differential oil?

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drivesafejane
Posts: 35
Joined: Mon Feb 02, 2026 9:02 pm

Hello there,
Is it necessary to change the oil in the rear differential? I've noticed a slight drone coming from the rear of my S205 C220d Bluetec auto when travelling at faster speeds (on the highway), and I'm not sure what to use. Any suggestions? It is not apparent from any of the websites which one. Is there a liquid moly or other product that I can get instead of the £65 litter from MB?
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Loonie4cars
Posts: 37
Joined: Mon Feb 02, 2026 8:49 pm

With FE SAE 75W-85, Fuchs Titan Sintopoid


could complete the task.
I don't think having a drone will solve the problem, though.

These noises are also notoriously hard to identify. The trouble might be worthwhile if it meant never having to deal with a binding brake or parking brake again.
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madmadmax
Posts: 43
Joined: Mon Feb 02, 2026 9:01 pm

Do you see any indication that the Differential is leaking?

Assuming this is the case, why are you so sure? A wheel bearing or a worn tyre is more probable the culprit. I would be surprised if changing the oil fixed the differential.
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drivesafejane
Posts: 35
Joined: Mon Feb 02, 2026 9:02 pm

Hey there! Just wanted to let you know that there's this tiny drone that becomes louder at 75mph (but no one else seems to notice). I had it checked out this morning, and it doesn't seem to be binding or bearings.
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madmadmax
Posts: 43
Joined: Mon Feb 02, 2026 9:01 pm

The gradual wear and tear on certain tires can produce a drone sound.
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drivesafejane
Posts: 35
Joined: Mon Feb 02, 2026 9:02 pm

Much obliged for getting back to me; I'm thinking it might be a worn tyre because it's near the wear bars on that side. It's not the bearings, and there's no leak; I jacked it up. It would be beneficial, I suppose, because I've read that the differential oil should be replaced every 50,000 miles or such.
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madmadmax
Posts: 43
Joined: Mon Feb 02, 2026 9:01 pm

Changing it won't harm anything, but making the modification is highly unlikely to fix the problem.

In order to change the oil, unplug the fill plug first 👍 😁.
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landy_110
Posts: 19
Joined: Mon Feb 02, 2026 9:04 pm

The tone of the diff noise typically shifts from drive to off drive as you release the throttle pedal.
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Loonie4cars
Posts: 37
Joined: Mon Feb 02, 2026 8:49 pm

Because changing the diff fluid isn't expensive, I guess you're right that it's probably the culprit.


But it may be a prop bearing, a resonant bush or even tire noise.
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HABIBI_JOHN
Posts: 30
Joined: Mon Feb 02, 2026 9:03 pm

Problem with the exhaust bracket?
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