Trans Fluid Change - ALL or NOTHING why??
Thread Starter
Super Member
Joined: Oct 2012
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2026 GLC300 4Matic (X254)
Trans Fluid Change - ALL or NOTHING why??
So we all know the importance of keeping fresh fluid in our 7G/7G Plus units. But so many have the concern that the torque converter fluid is not changed when dealer does service. And none of us really know if dealer changes it unless we watch. Qty of units on invoice doesn't mean squat...at my dealer anyway.
So, what's the science behind adding new fluid to old fluid? Does the new juice really become completely worthless by being contaminated by old fluid? Or is some new fluid in fact better than no new fluid at all?
So, what's the science behind adding new fluid to old fluid? Does the new juice really become completely worthless by being contaminated by old fluid? Or is some new fluid in fact better than no new fluid at all?
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Joined: Jan 2009
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From: Southwest USA
Another round of ICE
Why are you even considering this as an all-or-none situation? This issue is no different from any other with the same concept. If you buy a gallon of fresh milk, the overall milk is fresher than if you mix in last week's leftover milk. The fluid is not worthless, but it's not as good as it should be, and the benefits are reduced.
Thread Starter
Super Member
Joined: Oct 2012
Posts: 583
Likes: 24
2026 GLC300 4Matic (X254)
I've read that people say a partial change is worthless, that's why I was asking. If there was something special about the science or fluid behind those claims. I can't make the leap to milk, as it's not a scientifically developed fluid. Obviously, I wouldn't drink spoiled milk, even if someone poured half a gallon of fresh into it. Not sure if that applies to synthetic fluids though.
MBWorld Fanatic!
Joined: Jan 2009
Posts: 5,113
Likes: 57
From: Southwest USA
Another round of ICE
I've read that people say a partial change is worthless, that's why I was asking. If there was something special about the science or fluid behind those claims. I can't make the leap to milk, as it's not a scientifically developed fluid. Obviously, I wouldn't drink spoiled milk, even if someone poured half a gallon of fresh into it. Not sure if that applies to synthetic fluids though.
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From: LA LA Land
'08 C300 MM Pano
Its pretty simple really... If the fluid in the transmission has reached a stage where it it recommended that it be changed due to the fact that it may not be offering the protection is needs to offer, then oil that is in the torque converter which, presumably, has been used over the same time period and has subjected to the same restraints driving conditions has likely reached the end of its useful cycle as well.
