Usually you want your engine to run around 160-170F more than the ambient temp is.
For example if it's 60F outsite then the safe engine temp is around 220-230.
If it's 90F then 250-260.
But this is all theory since the engines cooling head, the body, the gearing, the track,... all affect the engines temps.

Of course you can't run it for 5 minutes and say it's OK at 250 that it temps now and later on you go and run a 40min final and expect it to stay there...!!

There is also a point where the metals of the engine will start to wear out much faster at a given temp which for each engine this differes.