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.
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.
probly bad gauge or loose wire buy a manual gauge one with the oil line right to the gauge nothing is wrong. the guage is supposed to be high when driving. it will drop when you stop or are idling.
i have a 1990 ford ranger and my fule gauge always reads full, why?