Hummm - not sure about the oil temp sensor, if there is one. Just been out in mine to check a couple of things I sorted at the weekend which needed me to open her up a bit (past 5000 rpm) to check I have solved the P1518 fault code which I have!

Oil temp on a 20 mile round trip stayed around 1/2 to 1/3, pressure fell a bit as the block warmed up.

Difficult to find a wiring diagram for the ST170 but I haven't seen an oil temp sensor - normally on the oil filter housing. I will look when I have a chance!