I have a 93 S10 Blazer with approx 128K miles. Just over a week ago I noticed the engine was running around 10-20 hotter (210-220) than normal and I added just over a gallon of coolant to the radiator. The car had always run right at 200 according to the dummy lights and has run between 200-210 ever since. It will go up to 210 when running, dip down to 200 when stopped, and vice versa. It will run at 210 consistantly for 30-40 minutes and then dip down to 200 for a while and then back up. It hasn't overheated (or gone over 220) but this change has me puzzled. It never went over 200 until this past coolant adding episode.
I have replaced the thermostat, water pump (it had a small leak), and even the radiator cap but it still deviates from 200-210. is this something I should even concern myself with? Could it be a sensor error? I haven't flushed the radiator. Could this help?