Is the engine sealed, can you spot a leak, is the fuel tank and lines good and in what kind of vehicle is this?

At 300f if the engine is still running good or somewhat properly but hot then you could have a slipping clutch, dragging brakes or a bearing going out in the car. Usually when tuned improperly and running that hot they will eventually stall. But when running that hot and will still perform ok that usually means the tune is close but there are factors causing the excessive heat. Take a look around and see if there is anything you can find wrong.