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I've been using this app on a tablet ($8 for the Pcars key) https://play.google.com/store/apps/details?id=de.barz.hud_dash&hl=en
And it can display oil temperatures among other things and you can set thresholds for each thing.
I will say get this app like /r/DRIFT2EZ said as well, if you hit ANYTHING with the front or rear of the car, it will cause aero damage and prevent air from getting to the car, How much air? depends on the damage of the cars aero.
It's usually a phone or tablet running something like DashMeterPro, Hud Dash or a second small monitor running something like Z1 Dashboard.
There's a lot of others out there too. Many of the PC based ones can stream over a network so you can display the hud on another laptop or pc.
Also, there are a lot of hardware options available. Some examples here: http://www.leobodnar.com/shop/index.php?main_page=index&cPath=97&zenid=5e980467e4e251e8720d7ea1305c43d5
quite a number actually. For example Dashmeterpro, rfdisplay and HudDash should work with most simulators out there.
For codemasters, they usually have a function where they will output telemetry data to an app or software of your choice. I use HudONE for F1 2016