OK, well I am having this same issue. I have spent over a thousand dollars SO FAR. Both fans were replaced, the reservoir was replaced, the thermostat/housing/gasket were all replaced with NEW parts. So NOW the mechanic tells me that it is "something electrical" causing it to go to HOT before it even has time to really heat up. (no kidding) - That they tested the HEAT of the engine, it is not running hot, but but by simply messing with the ignition (I guess jiggling the key is what he was saying), he could cause the temperature gauge to go up and down, BUT like I told him, if it is not overheating, WHY when it goes to H in 30 seconds, does my A/C start blowing warm air suddenly, then it goes back to normal on the gauge, and air blows cold again. This is BS and I would really like some answers without having to replace MORE parts that apparently do not solve anything.