Most modern vehicles have closed radiators that do not allow you to check the coolant level. Your vehicle owner’s manual should tell how to check the coolant level, if possible.
While you can usually rely on the engine coolant temperature gauge on your interior dashboard, there are countless things that could go wrong to cause the gauge to read incorrectly. Most vehicles have a coolant temperature sensing unit that sends the information to the interior gauge. If the sensing unit goes bad, your gauge could show that the temperature is cold or warm, even if the engine overheats.
If your vehicle has a radiator cap, check the coolant level at least once a month. DO NOT ATTEMPT TO REMOVE THE RADIATOR CAP WHILE THE ENGINE IS HOT. Let the engine completely cool off first. Slowly remove the cap to release any residual pressure inside the radiator. Make sure the radiator is full to the bottom of the filler neck.