My heat guage has jumed one bar over the center bar when ideling in traffic. It is a 901/2 model purchased new in late `1990, now having 43000+ miles on the odometer. I have had only minor problems, this being one of them. Anyone with some knowledge please let me hear from you. Hwalker426@aol.com.
My service manual says the operating temperature is between 185 and 230 degrees. If the temperature exceeds 259 degrees the air conditioner compressor clutch will disengauge and code B450 will set. I would guess that yours is similar. I have a 1993 and the thermostat is a 180 degree. Your temps are within range, but if you feel better, go ahead and install the 160.
I hate to send you to another board, but there was some pretty extensive discussion on this on the AAG board. Unfortunately, we/they are having problems with the domain registrar. Normally, the board would be www.allantenet.org, but due to the problems you have to get there via http://184.108.40.206.
Do a search on something like thermostat (make sure you set the max age something large, like 500 days - it defaults to 7).
There are a couple of issues. Depending on the situation, what you see could be normal. If it isn't normal, you're looking at potentially the cooling fans, the cooling fan relays, the thermostat, or possibly, a blockage caused by poor cooling system maintenance.
Pay particular attention to any posts by Jestal, as he is a GM powertrain engineer who worked on the Allante line, among other things.