40C at idle = too cold
85C at idle = just fine!

Given mass-production temperature gage and sensor tolernances, I would not worry +/- 5C, so 80-90 is OK. It's more about how much it moves, or does not move with changes from idling to highway cruising. If it idles a few degrees warmer, and cools right off, you are doing fine.

Best Regards,
Jim