Reading HAARP talk about multiple heat gauges and heat capacity gave me an idea. I'm not really confident it's the right way to go, but I thought I'd throw it in and say how I think it'd change things if implemented. However, it might let us have our cake and eat it, too. We can have realism and good gameplay.
I got to thinking about how the ΔT between the mech and environment, and how that may be causing problems with gameplay. But then I realized, a mech might not actually dissipate heat that much faster when its internal components are hot, because the armor and other exterior components actually should act as an insulator. Heat does pass through, but more slowly. We can treat the interior and exterior of a mech as having their own thermal capacities that slowly come to equilibrium.
What if instead of a gauge that gives the temperature of the mech in terms of a percentage, we used an absolute scale of thermal capacity? A mech's tonnage would be divided between Internal and External mass. The Engine is not included in the following calculations, because its temperature and thermal impact should be pretty much constant while the mech is active (and when it's not active, the HUD is turned off). Internal mass is weapons, ammo, the skeleton, computers, cockpit, MASC, etc.. External mass is everything else (including JJs), I guess.
With ambient temperature, heat will move into the mech depending on surface area (an approximate constant value for each mech) and the density of the medium (vacuums have low heat transfer, air has normal heat transfer, liquids would have high heat transfer). ΔT X Density X Surface Area Constant = how fast the temperatures of the environment and the mech come to equilibrium.
The Internal thermal capacity is what is affected when you fire your LAZORZ, hit MASC, and just have the engine running. Normally, the Internal temperature should be higher than the External temperature, leading to a flow of heat outward. Heat Sinks, although part of the exterior of a mech, move interior Thermal Capacity directly to the enviornment (Ambient) at a rate dependent on ΔT X Density X Heat Sink Number X Heat Sink Type.
The External thermal capacity only increases on its own from the use of Jump Jets. Otherwise, it is only affected by its environment (Internal and Ambient).
So... what makes this system different than what we have currently? Well first of all, it changes how heat weapons work. Flamers, Inferno Charges, and other heat-changing weapons, environments (hot or cold water), and events (nukes?) ONLY affect the External Thermal Capacity directly. This External Thermal Capacity changes slowly due to being unable to be cooled by Heat Sinks, so continued Flamer use can saturate a target's External Thermal Capacity (by "saturate" I mean raise its External temperature until it is higher than the Internal temperature). Once that is done, not only do the Internals lose a source of heat dissipation, but they actually slowly gain heat from the Externals. Above a certain point (a percentage of total External Thermal Capacity), the armor becomes soft and easier to damage. If the External Thermal Capacity is maxed out, further heat damage is done directly to External components (namely armor, jump jets, and heat sinks). Without Heat Sinks or a flow of heat to the External components, the Internal Thermal Capacity will continue to rise until it comes to equilibrium with the External Thermal Capacity. Once all External components are destroyed, heat damage is dealt directly to Internal Thermal Capacity.
In this way, thermal attacks don't instantly kill you, but their effects are long-lasting and if ignored, they can lead to your destruction.
This means that mechs with more armor can tank more thermal attacks, and mechs with more weapons can generate more heat internally. With this, a Blood Asp has more capacity for a larger alpha strike than an Owens, and an Atlas can endure a lot of dedicated flame attacks. That said, lighter mechs are much harder to hit with flame attacks, and can get out of hot environments faster.
This also means that while shutting down will keep your internals safe for longer (by cutting off all sources of internal heat generation), your External Thermal Capacity along with your armor, heat sinks, and jump jets, are still at almost the same amount of risk. Shutting down buys you time for someone to rescue you, it doesn't reset your heat to 0 after a few seconds.
Why an absolute scale? It gives you a feel for the strengths and weaknesses of your mech, and it standardizes the thermal effect of certain actions. Firing a Medium Laser will ALWAYS raise the Internal Thermal Capacity the exact same amount. Likewise, getting hit by a Flamer will always raise your External Thermal Capacity at the same rate, regardless of your asset.
The direction of the arrows and number of arrows in the example UI depends on the direction and strength of heat flow. Arrows always indicate a flow of heat; if no arrow is present, the two aspects are in equilibrium. This allows a pilot to get an idea of their sources of heat. They will know how serious a Flamer attack is compared to their own generated heat, and can prioritize more easily accordingly.
In said system, coolant flushes would cool internals, but wouldn't directly cool externals. So you'd be able to fire lasers and stuff again, but you'd still have inferior cooling long-term, until the externals finally cool down.
It'd be cool if enemies could get a reading on your External temperature when locked.
In my little picture above, an example is shown where the Internal Temperature is relatively high (perhaps the player just used an alpha strike), leading to a large temperature gradient between the Internal and External components. Over the next few moments, the Heat Sinks will reduce the Internal Temperature and the External components will slowly come to equilibrium with the Internal. In this picture, the External components are actually cooler than their environment. It could be that the mech just ascended from cold water, and ascended into somewhere hotter. Under normal circumstances, the flow of heat would be outward, with Ext having a higher temperature than Amb. But in this case, both the Amb and Int are heating the Ext of the mech.
Anyway, this proposal is pretty far out. But that's half the reason I did it. Maybe something so different can be useful to someone.