I picture an ideal heat system doing something like the following:

In thiis case, this is a Madcat who is walking (negligable heat from leg actuators) and fired his LRM20s. The heat 'rings' spread out from heat sources to represent spreading heat. High heat can affect certain areas (a small laser sandwiched next to two large pulse lasers will have degraded performance from the hot weapons regardless if it were fired. Or in the case of the madcat, the machine guns are kind of warm, but not enough to be impacted at all. Furthermore, if the Cat fires its CERLBLs, the CERMBLs will be pretty hot as well.
Heat spreads. Heatsinks are good at rapidly cooling specific hotspots but less good at overall cooling. So the orange LRMs could be cooled but the gradual heat level (the lighter colors) will not cool as rapidly - cooling after all is faster the larger the temp. difference.
So a sprinting Novacat could fire all its weapons and cool the weapons down, but the heat will spread all over the body VERY rapidly (basically rippling like a rock in a pond) and will cripple the mech before long.
I could better represent this if I had more time and, more importantly, .gif animating software... but I don't

You'll have to use your imagination.
Anywys, just a thought.