The GAU8-A tends to overheat and jam if fired continuously. Gatlings DO jam.
Really?
Yeah. I used to play Silent Thunder 
Not a very reliable source, in other words?
From what I've been able to find, the chance of jamming in a chain gun (externally powered gun) is in general exceptionally small.
During testing of the L94A1 gun, 101,343 rounds were fired without a single jam.
That gun is not a gattling gun, but the main liability for fast firing weapons is often misfiring rounds, which chain guns are unaffected by.
Gattling guns like the GAU-8 also have a linkless feeding mechanism, reducing the chance of jamming even further.
Anyway, since MWLL "has NOTHING to do with real life or anything like that", what I wrote above is irrelevant.
I think coolant in tanks should be possible to use to cool down the weapons; there is little other use for it. Weapon jamming could then be simulated with actual jamming, but certainly not disguised at overheating in some obscure way. I can accept overheat for balance reasons, but then it should simply be explained as just that.