I have A 1989 Toyota 4 runner. I bought it in the summer, had no problems I've been fixing the little bugs on the vehicle back window, wiring ect. Now that the cold weather is hear I have a new issue where my coolant temp go's cold after being at operating temp while idling and when driving over 55 mph the temp go's cold. I replaced coolant, thermostat, temp sensor to gage, temp sensor to ecu. I pushed forced air through the temp sensor out the lower radiator hose. I also removed the coolant temp sensor and installed a after market gage that tells you the degrees. I allowed vehicle to warm up to 165 degrees F. and was able to hop on the freeway and make it one exit as temp dropped to 100 degrees. I used a temp gage on front of engine from harbor freight and it says radiator is 180F at radiator and thermostat is 172F and front of block is 195F and back of block by sensor is 165F. I find people move the sensor to the front coolant hose by timing belt. I'm not excited to drill a hole in the bracket is there a fix to my concern and has anyone have this issue. I don't want the engine to shoot up in temp and over heat without knowing.

after driving will go down to 100degrees F

while idling will jump to 180degrees F