Mobil 1 Racing 4T… in a Prius?!

[kschachn]

You could do that, but winter might not be much of a concern in any case, the current version has a -48C pour point and seems to pump pretty well in cold cranking. The 2005 vintage may have been even lower...

Which isn't necessarily correlated to cranking and pumpability, if the oil met the performance requirements for a winter rating better than 10W it would be labeled as such.

 

[2005jettatdi]

I used some in my Model A and it seems to be working fine. I am sure that using it in a Prius would be the same.