So I went back to the dealer, they took it in for 10 mins and brought it back washed (nice), with oil temp display working! I asked the salesman what the problem had been and he told me:
"There are different service packages, they used the wrong one. Sorted. It was all on the computer"
Doesn't make that much sense to me but at least it seems that it was software not hardware. Average oil temp is about 92C. It certainly takes quite a bit longer for the oil to get up to temp than the water...
