How hard to turn should a new water pump be?

I mean it’s just some seals and bearings no matter who makes the pump it should still be able to turn by hand.
Well, there's a certain expectation of Quality Control with a Mercedes dealer part and the OEM supplier is an important measure of that quality.
And, the OP apparently hasn't replaced one before so he's making sure all is right. That's the point of this forum and a very appropriate thing to do.
 
I think that says all that anyone needs to know. Return it.

I have to hop on and say. It should turn and not be loose flopping all over the place.

Sounds like you got a bad part, dont even waste any penetrating lubricant on it.. The joys of NOS or New Old Stock.
 
I have to hop on and say. It should turn and not be loose flopping all over the place.

Sounds like you got a bad part, dont even waste any penetrating lubricant on it.. The joys of NOS or New Old Stock.
It isn’t even NOS. It has a 2017 casting date on it. Given how long water pumps last, this is a pretty recent run.

Penetrating lubricant isn’t what I’d consider for a cooling system part by any stretch. But tight seals that are lubed by glycol is part of my curiosity…. If folks were to say that they’re all that way until the system gets filled up and all the seals and interfaces get wet…
 
It isn’t even NOS. It has a 2017 casting date on it. Given how long water pumps last, this is a pretty recent run.

Penetrating lubricant isn’t what I’d consider for a cooling system part by any stretch. But tight seals that are lubed by glycol is part of my curiosity…. If folks were to say that they’re all that way until the system gets filled up and all the seals and interfaces get wet…

I think you're overthinking that part.

It should turn freely, unless there is something I dont know.

Same for alternator, as far as I know... I think you're asking what is the tightest it should be in resisting turning, and be okay.
 
It isn’t even NOS. It has a 2017 casting date on it. Given how long water pumps last, this is a pretty recent run.

Penetrating lubricant isn’t what I’d consider for a cooling system part by any stretch. But tight seals that are lubed by glycol is part of my curiosity…. If folks were to say that they’re all that way until the system gets filled up and all the seals and interfaces get wet…
Several members here have told you they've changed MB diesel water pumps and new ones can be turned by hand. There's some resistance, but not difficult nor needing much force. This one isn't right.
 
Several members here have told you they've changed MB diesel water pumps and new ones can be turned by hand. There's some resistance, but not difficult nor needing much force. This one isn't right.
Yeah.

Hard to believe, though honestly it wasn’t that expensive.
 
It is incorrectly assembled total junk!

I was watching this hilarious movie on Amazon Prime about an Italian faucet "fabbrica" boss and worker. Perhaps this pump was assembled in that fabbrica. :ROFLMAO:


That said, looking at my OEM repair manual for 1985 Corolla (RIP), it seems tedious and difficult to properly disassemble or reassemble a water pump. If the factory worker isn't paying attention, things will go wrong.
 
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