When as a crew we had a coolent leak (indicated by engine temp/visual) the AFV is shut down, period. There is "no randomization of how much".This is done to prevent more leakage/damage. Your wish if this is, the case is wrong. Same goes fuel leaks, this damage is very dangerous to the crew, the AFV is shut down till it is fixed. We can drive while this is indicated in the sim true, in battle one would do certain things to stay alive,the sim teaches the consequences of such decisions, mostly the AFV becomes noneffective shortly....as it should.
You can move to a safe place and shut down to repair most issues given the mission times,this may or not meet these times. But you can do as you wish already