Most importantly, I'd do a bypass of the blasted (*#&(#! temp compensator board in the instrument cluster. There's no sense in paying any attention to your temp gauge till you get rid of that thing and put a jumper in place. Do a search here for the procedure. If a good search comes up empty post back here.

Could be the temp sensor is reading hotter than actual. It's under intake runner #2. Wire lead to it is NOT 12V. I believe it's 10.2V. At any rate that voltage is set by a small voltage stabilizer on the rear of the instrument cluster, serves the temp and fuel gagues.

Did you examine the old bent t'stat for missing parts that would fall down the bypass channel in the head/block?

Another way to confirm temp. is to go to an exhaust shop. They usually have a gun-shaped infrared thermometer that will read temps off anything.
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Sven: '89 245 NA, 951 ECU, open-front airbox, E-fan, 205/65-15's, IPD sways, E-Codes, amber front corner reflectors, quad horns, tach, small clock. Wifemobile '89 245 NA stock. 90 244 NA spare, runs.