Thank you PaulS for your quick reply.
I don't know how the smiley came in there, of course it means "8".
The temperature is returned in 12 bits + sign(msb) = 13 bits. (while negative temperature can't occur in my application).
These are the msb bits, the LM 92 returns. The lower 3 bits are status bits, unimportant for me, therefore ">>3".
I don't think, it's a software problem because it gets worse the longer the cable is.
I just can say about the msb, that there are to much "1" read by Wire.read(). The lsb represents to small temperature differences to verify.