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[kkrover]

Help- i've been wrestling cooling issues for a year now on my 95 3.9 RR SWB. New head gaskets, radiator, fan clutch, hoses, etc.. but still having issues.
The car doesn't seem run hot since the new radiator last month, and also doesn't seem to loose coolant as level in tank is constant. It does, however, always have air bubles in the cooling system, as I can hear them gurgling in the heater core, and it will also randomly and intermittenly push coolant out the cap when driving on the highway. Have done the carbon test on the coolant and is negative, so I don't think it is a leaking HG or bad block. I have been driving it and checking temp regulary to try to figure this out, but it seems totally erradic. Timing is properly set, and car runs great, but just ramdonly pushes coolant and always has air bubble sound in heaater core (which is driving me nuts). I have bled the coolant system multiple times and air bubbles in heater core go away but always come back in a few days.
Running temp, taken on top of radiator at top hose, ranges from 191-198 (f), with occasional jump to 203. Both times this weekend on the highway when it pushed coolant, it was 192. Would check again an hour later, no coolant had been pushed out, but radiator was 197 degrees.
What could cause pressure in the systemand the fluctuating temp?