90 cel is the correct operating range, although the fact that all your other guages go goofy when it gets hot is something really strange. Perhaps your car is trying to tell you something? ha ha. I would recomend checking the grounds, there are bunches of brown wires gathered up and grounded to the chassis in several places, loosen and tighten to refresh the ground, next if you have not already replace every fuse, those type of fuses are tricky and cause irregularities in contacts and even burn out without any visible evidence. Then I would check the temp sensor sending unit, make sure it is not creating a flat ground to the IC (instrument cluster) the temp sensor signals temp by level of resistance and if it is goofing up it can likely cause other errors as well, when it hits that temp it may go to registering no resistance and freak out your IC. Give those a try and report back. Good luck! If you need help identifying the Temp sensor let me know.
Brian

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Brian W. Heitman

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