About three weeks ago on the highway the temp. gauge red lined on my 96 Accord V6 2.7L (with 200,000 miles). I pulled over/saw steam from the resivoir tank. After cool down, I filled it with 50/50 antifreeze & drove home with the heat on high. I checked for leaks with the heat on & did not find any. I have since been keeping a close eye on the temp gauge; which has run at the normal temp line & the fluid level in the resivoir tank has not shown any fluid level loss/leaks either. The car has been running normal since then until 3 days ago when the same thing happend again on the highway at 75/80 mph; I watched the temp gauge gradually rise to near red line, so I slowed to 60/65 mph & it began to drop back down to just past 1/2 way. Five minutes later after arriving home I checked the resivoir tank which was bubbling/slightly leaking over. With the car off I let the fan run & watched bubbling fluid syphon back over to the radiator from the resivoir until it was empty. I refilled the resivoir and the car is fine again. This ONLY happens when I'm on the highway at 75+ mph. Does this sound like a stuck thermostat issue?