I was having cooling issues with my 88 (until Eagle set me straight) new radiator, new surge tank (and cap) and plugging up the leaks, took care of most of the problems. Also replaced the thermostat with an OEM, which has a air bleed hole, to help move the air along. New fan clutch, is my next purchase, installed a manual switch for my aux. fan, just in case. Simple installation, bought a 10 foot piece of two lead wire, already insulated and piggy back spliced (soldered) the two wires onto the thermo switch leads, near the connector and ran it beside the harness, to a switch inside. Tested my temp. switch (lower left of the radiator) in a pan of boiling water, with a ohm meter. Tried 2, they both switched at about 207F. Haven´t tried a new one, have heard they switch on (close) at a higher temp.
When I refilled, I removed the gauge, sending unit, at the drivers side rear of the block and filled until coolant came out. Then topped it off, with the sender back in (do not use sealer/messes with the ground). Top radiator hose is an air trap, squeezing it together a few times, moves some more air along the system.
Had an 87, after most any kind of radiator service, it would blow some steam, unless I had thoroughly, burped most of the air through the system. Air gets trapped on top, causes a partial blockage, possible the temp. switch for the fan, at the bottom of tha radiator doesn´t get hot enough to turn on, even though the top is blowing steam, seen it happen.
Doesn´t take to much of a leak, to suck a little air at a time and have the air build up, to the point it messes with the flow, then everything overheats. System builds pressure and forces a little coolant out, then when it cools down it sucks a little air in, air moves to the top and stays there (mostly), eventually moves to the surge tank, hopefully before the motor overheats.
Last thought, the universal type thermostat gasket, doesn´t have the cut out for the surge tank/heater hose bypass. Bound to have an adverse affect on how the system works, if the gasket is covering the bypass slot.