Why do some people say 0W20 can cause more leaks compared to a 5W20?

[billt460]

Speaking of leaks, I've often wondered how NASA / Rocketdyne was able to seal the liquid hydrogen fuel lines and connections on the Space Shuttle's main engines? Liquid Hydrogen is one of the LEAST viscous liquids in existence. Not to mention the stuff was -423 F in a liquid state. Enough to make most anything stiff and brittle as hell.

And because of it volatility, absolute zero leaks could be tolerated. Not to mention that thing shook, banged, and vibrated for 8-1/2 minutes, from ignition, all the way into orbit. And it never had an engine induced fire in 135 flights.

 

[Schandyman]

They don’t know. Mobil 1 proved many of these statements as false. 5w20/0w20 are interchangeable if an engine is going to leak it’s going to leak. Not do to this.

 

[kschachn]

…

 

[kschachn]

Speaking of leaks, I've often wondered how NASA / Rocketdyne was able to seal the liquid hydrogen fuel lines and connections on the Space Shuttle's main engines? Liquid Hydrogen is one of the LEAST viscous liquids in existence. Not to mention the stuff was -423 F in a liquid state. Enough to make most anything stiff and brittle as hell.

And because of it volatility, absolute zero leaks could be tolerated. Not to mention that thing shook, banged, and vibrated for 8-1/2 minutes, from ignition, all the way into orbit. And it never had an engine induced fire in 135 flights.

Helium labyrinths for rotating joints in the turbopumps and metal seals in static joints.