The temp sending unit or gauge is bad, probably the sending unit.
Test gauge function with a mechanical gauge to get actual engine temp.
Because the gauge is broken.
Your car engine isn't getting up to the desired temperature, about 130 degrees Fahrenheit.
If the temperature gauge on your 1995 Blazer with a 4.3 engine stays on hot but the vehicle is not actually overheating, it could indicate a faulty temperature sender or gauge. The sender might be providing incorrect readings, or there could be a wiring issue affecting the gauge's performance. Additionally, a stuck thermostat could cause fluctuating temperatures, but if the engine runs fine, it's likely an issue with the gauge itself. It's advisable to have the sender and gauge tested to confirm the problem.
Most likely cause is a failed engine thermostat.
There are pages and pages and items that can cause a check engine light. You need to have it checked for codes with a scan tool. After repair light can be shut off with scan tool.
Cars run better when the engine is warm. Thermostats stays closed to prevent the water from going through the radiator to be cooled until the engine has warmed to the desired temperature. Then, it opens to allow the water to be cooled to prevent the engine from getting too hot.
With no make/model/year/engine information to work with...The temperature gauge is driven by a simple sensor that is both cheap and easy to replace.Any auto parts store will be able to help you find it on your engine, and of course more than happy to sell you one.
Thermostat is sticking.
The thermostat is the most likely culprit. The major clue is that the engine temp stays in the lower middle of the gauge - the heater core would not cause this. The thermostat is most likely stuck in the open position - needs replacement.
The gauge, wiring or sending unit is bad.
The normal operating temperature for a 1996 Camaro typically ranges between 195°F and 220°F (90°C to 104°C) when the engine is fully warmed up. It's important to monitor the temperature gauge and ensure it stays within this range to prevent overheating. If the temperature exceeds this range, it may indicate a cooling system issue that needs attention.