Background on the car, 340K miles, runs fine, new radiator and hoses (Orelly's) 2 years ago, new OEM tstat about a month ago, doesn't seem to be leaking any coolant.
Car began intermittantly running at a temp slightly higher than the temp guage's normal spot, and has been running warm some days, and running in the normal range other days.

Well, the thing started going up on me last week when I was coming home from Columbia MO. The weird thing is, the gauge ACTS like it works (goes to its normal spot, then IF it decides to get hot, when I turn heat on full blast it goes down a bit, and if I coast to a stop it will move up, and when I start moving again/ rev the engine, it goes down), but the other day while driving the gauge had moved up to about 75% to hot, and then just cruising down the highway, it dropped down (sudden drop) to it''s normal spot, stayed there for about 100 miles, then started easing up again.

This morning I drove about 250 miles with it doing fine, then it started creeping up. I stopped to check the level in the overflow (doesn''t seem to be losing any coolant) and fiddled with the rad cap, and heard a whoosing sound as coolant was allowed to go into the overflow. I dove for about 45 min with it in the normal spot before it started easing up again. I thought it might be a bad cap (not allowing fluid to go in/out of overflow tank) so I replaced and still no change. This thing will run warm for an hour, then go to the normal spot for an hour, then run warm for another hour.

The good news is, I''m buying a family member''s 94 accord to use for my traveling. The bad news is, I need to figure out what''s wrong with the cooling system on this one before I can sell it.

Anyone have any ideas?