I recently had intermittent high heat problems, including some indications of coolant loss around the area where the top radiator hose connects to the thermostat housing and at the top of the water pump, near the o-ring.

I changed the thermostat, still ran hot occasionally, especially when the AC was on and I was on the freeway above 70 mph.

on a cool nite, with no AC, the thing would run for hours with the temp needle at 9 o'clock, no problem..

So, I changed the fan clutch ($80 lifetime warranty from AutoZone)..no change.

Took to radiator shop, told me in two minutes, it was a clogged radiator. Bought a new one for $105 and no more problems. took old one to shop, they took off end tank and showed me 60% of tubes clogged, no flow. That dang radiator was new 22 months ago. From now on, I use distilled water, not tap.

My point is ... if your water pump is good, it is trying like hell to push water thru a clogged radiator, and that high pressure coolant is gonna go somewhere..and if it can't squeeze out the hose connections, it is gonna shoot out a weak radiator cap..and of course, as the coolant cools, a slight vacuum will be created to suck all the coolant out of the overflow tank, and back into the radiator.

good luck,