engine overheated from leaking hose. Added stop leak,coudn't find the exact location at first. Worked for a couple of days, then overheated again. Let cool down for 5 min., trickled water into radiator to cool down and fill. Changed hose, ran fine for a couple of months. started to run warmer than usual,(midrange), no signs of leaks. Topped of system every week or so. Temp spiked at top of range, (freeway at night, 70 degrees outside), then dropped to midrange. Roughly 10 miles of freeway driving. Drove another 10 miles,(freeway), gauge fluctuating every 10-15 seconds from top of range to lower 1/3 range mark. Changed thermostat, flushed radiator and system. No change. Changed other hose, same thing. Changed pump, tested thermostat again. Gauge spikes to 3/4 range within 2 minutes, then drops to 1/3 for 5-10 seconds, then spikes again in 5-10 seconds. Ran with garden hose in radiator neck, same thing. When cap is off, gushes from neck after 45 seconds, not a steady overflow. Upper hose runs hot as well, lower hose stays cool. Suspected bad heads or block from first overheat. Had both checked. 1 head near warp limit and corrected. Now overheats within 1 minute, the rest is the the same. No problems at all before this mess. Next step is dynamite!