VTEConly

It's a '97 DX HB with 135k mi. on it. I noticed the last couple of days that when I go 75mph (indicated) or higher the temp. gauge starts climbing to 2/3 or 3/4 of the way up. It NEVER went passed the thermometer picture before. It was always under that, and steady. I tried turning the A/C off, thinking it was that, no good. The FAN works fine, as does the AC fan. But I 've noticed the fan comes on a lot more often now and stays on longer (maybe because of the 90deg. weather we 've been having?).
The dealer replaced the radiator fluid at 91k mi. when they did the timing belt and water pump. I hope it's just the thermostat, and not a sign that the head gasket is going or the radiator.
I puzzled why it only does it at 75mph & up. I guess because the engine gets hotter and more fluid flows through the thermostat? Not sure. Does anyone have any ideas? I 'm almost ready to go out and buy a thermostat but I want to make sure. I think it's a little too soon for the head gasket to go, but you never know. I 'm not ruling out a water pump or radiator either but I have NO leaks. Thanks for your help guys!

9five1five

if its that old of a car it might just be overheating cuz of the hot weather on the highway man. it never OVERheated did it? my car has only done it ONCE and it scared the crap out of me, it only went to like 3/4 of the way though. if youre really scared on the highway, roll down your windows, turn the temp. control to full heat, select defrost on the vents and put the fan on 4, thatll cool her down.

DragII

If the temp fluctates...its most likely the thermostat

VTEConly

thanks guys. Yeah it didn't do it this morning going to work at all and I 've never noticed it "overheating" (if you can call it that, it never reached the red and the antifreeze was not boiling) before. This was the 1st time. It could 've been because it was really hot and humid. I don't know if I want to turn the heat all the way up when it's in the 90's out with 98% humidity! But it did scare me though. It did it 3-4 times during my 80mi. trip back home Wednesday but never went more than 2/3-3/4 of the way up. I 'll replace the thermostat just in case.
I was looking for white smoke in my rear view mirror to see if I 'm burning any antifreeze (head gasket) but I couldn't see any. The reservoir was full when I got and there are absolutely no leaks under the car.
When should I expect the radiator and head gasket to go? My friend's head gasket went at 160k mi. on his '91 Civic and a co-worker's '92 Civic head gasket went at 190k. Don't knokw about their radiators. I would guess the head gasket depends on driving habits and city/hway mi. ratio.

not so civic

if you have the stock dx? radiator, upgrade to the dual core sir from http://www.radiator.com. if you can't afford a radiator and you have automatic transmission cooling ports to the radiator, run a line from your throttle body coolant line in and then out of the auto tranny cooler plugs and back to wherever the tb hose goes to the block. basically route the unused radiator section to the throttle body coolant line. make full use of your radiator. if you don't have those holes in your radiator, get a auto tranny/oil cooler and route to that and just mount it on the bumper.