120 is getting pretty high if that temp is sustained. I think a range of 90 to 100 is good. The Roush dealer that I bought my motor from said that my
oil temp could reach as high as 110, which it has on extremely hot days when I'm climbing a long uphill grade.
Could be a bad gauge. What weight
oil are you running? Also, is your water temp fine (i.e. steady at 90 c)?