engine temp goes up at highway speed

[GTcelica22]

hey everyone:

1994 celica GT 2.2L

Just happened last night, i was driving on the highway when i noticed my temp needle was reading about a 1/4 of an inch higher than normal. That's never happened before. It's always been rock steady right in the middle. I was doing about 80 miles an hour. i slowed down to about 65 and the needle went back to the middle. I sped up to 70 and the needle went back up again. So i slowed down again and it went back down.

Tonight i was on the highway again, but due to the freezing rain and hail, i was doing between 40 and 60. Tonight the Gauge never moved from the middle. It was steady all the way until i got on the off ramp at the light, Then it went up and came back down by itself. I didn't hear the fans come on. I went to a local parking lot to do some tests. I parked the car (gauge was in the middle), and reved the engine to raise the temperature. It went up and then came down. Fans did not come on. Strange. I them went back to my house. parked the car, put the hood up and tried to make the fans some on. Here's where it gets interesting...

while in my drive way, the needle goes up, both fans come on high speed, needle drops. I then tried to do it again. Reved the engine for a second, i hear both fans come on high speed, but the needle is in the middle. It did the same thing again with the needle in middle again.

There are no external leaks. engine oil is full. Both fans work, but on high. There is no debris covering the radiator. I replaced the thermostat around april 2011,( it was not a genuine toyota part and didn't have jiggle valve. is that ok? it's been fine all this time.) Timing belt and water pump have not been replaced (so i've been told).

Tomorrow i will check the coolant in the radiator, ignition timing, and check the radiator cap. What are the odds of it being the cooling fan switch or a relay? i only ask because it hasn't come on low speed since this happened. Will warm car up in drive way and see tomorrow.

[GTcelica22]

any preliminary thoughts?

[GTcelica22]

did some checks today:

There was plenty of coolant in the system. There was nothing blocking the radiator. both cooling fans work, no problem. Radiator cap looks ok, but bought a new one from the dealer just incase. Thermostat is good, but bought a new one at the dealer since i recall the one i put in doesn't have the "jiggle valve", whatever that does. And finally, i checked my ignition timing after driving it and that's good too (10 * with Te1 & E1 shorted).

I tested the temp gauge sender by disconnecting it. When unhooked, it drops all the way down. That's what's supposed to happen, right?

Not sure about the fans. They both come on at the same time at high speed and then turn off, no problem. i thought that the fan in front of the engine was supposed to come on slow sometimes. can anyone validate this?

I couldn't get the speed up today because of the rain. i will try again tomorrow to duplicate the problem. While driving it today, the needle didn't move from the middle. this car is very odd.