Hi again, I've been quiet for a few months. My 89 2.0Si has a weird overheating issue. The gauge will come up to normal (below half) in a mile or two and sometimes sit there just fine for miles and miles. The next time I get in the car I can drive 2 miles and the gauge will suddenly rise quickly to about 3/4 then go down to normal, then rise, and again fall. It can then go back to normal and sit there for the rest of the trip (mostly town driving) as if all is well. Things I've done: new timing belt and water pump 3K miles ago. new radiator, new radiator cap, new thermostat. Checked fans - o.k. - and definitely on when the a/c switch is on (which I leave on to make sure is on). I've tested compression - all 155-160 lbs. No white smoke, no evidence of leakage. Bled the system multiple times with the bleeder screw near the thermostat. What am I missing?